Why I do this!

Apologies, but a bit of self indulgence in this months blog. Every now and then it is good to take stock and just reaffirm why I do what I do!

I offer a battery consultancy service allowing my clients to access my experience of over 36 years working with, and developing advanced battery solutions. Benefits include;

• Accurate battery type selection
• Improved product performance
• Superior integration of the battery into a system
• Selection of the best supplier
• Reduced costs

Having worked for one of the largest manufacturers of battery solutions in the UK for so long, I often found myself meeting clients who, although they had a good idea of what they wanted, did not know all of the options available to them. Of course, my advice had to be tailored to the product portfolio of my employer. It was very frustrating knowing that there were better options out there from other battery suppliers that, until now, I could not promote.

Most development and design engineers will have spent some time learning battery basics and followed this up with looking at the various articles available on the internet covering battery matters. That’s fine if the battery manufacturers are putting like for like data in their publicity. But they don’t. This makes comparing products very tricky.

Knowing how a particular battery responds to the loads and environments required, especially whilst you are still developing the product is tricky. Yes, a supplier will do some lifetime and performance calculations for you, but if the goal posts are moving as your product develops, they will not be as keen when you go back again and again asking for the calculations to be repeated. Of course they will do it with a smile on their face, but this activity has a cost, and you can be sure that it will be recovered eventually.

So how much more convenient it would be to have access to someone who can do these predictions for you before getting a potential supplier on board. Especially as you will know they are working for your interests and not those of the supplier.

I look forward to helping you in the future!

Careful thought needs to be given to the interaction of the battery, the device it is powering, the environment it is operating in and the skill set of the eventual user. The availability of ever more powerful and energetic batteries, and the rules and regulations regarding transport and disposal, mean that battery selection is not as straightforward as seems at first. The use of an independent expert to give guidance to your design team can save a huge amount of time and cost to new project development. If you are interested in finding out more, please contact DM Power Solutions using the contact form on this website.

More of everything needs careful thought!

 
Not So Mobile Devices!
It was only a couple of months ago that I was writing about another product recall of rechargeable battery powered equipment. Now, just a few weeks later, there is another very high profile issue with batteries in a mobile device overheating and creating a potentially hazardous situation. So much so, this ‘mobile’ device is now being restricted as to which forms of transport it can be used on. A reported temporary software fix apparently limits battery state of charge to 60% until new ‘safe’ devices can be shipped to users. But what leads to these types of situations developing in the first place?

 
Energy + Power = ?
The drive has always been more energy in a smaller and lighter format, and misguided criticism of battery manufacturers has targeted the way battery performance has failed to keep up with the developments in electronics. When you look at the raw figures, yes the exponential increases in processing power look stratospheric compared to the pedestrian increase in battery power and energy density. But this overlooks a basic fact, the battery contains the potential to deliver energy whilst the rest of the kit just consumes it. If the µP is attacked with a hammer it will just stop working, do that to the battery and you will get a very different result!

 
Safe Battery Operation
The battery has to behave properly over a range of conditions, and great efforts are made to ensure that this is the case. Even abusive treatment can be tolerated to some extent. But the more energy, and the ability to deliver it at higher power levels, are demanded by users (and the reverse case of shorter charge times), the consideration has to be made of what happens to all that energy when the battery is abused. If the protection built into the battery is bypassed, either by an internal fault to the battery or external influence, all that energy crammed into a small space has to escape somewhere, and if the battery is designed to provide high power as well, then inevitably the result will be that things will get hot, very hot!

 
Triggers
Battery overheating due to external physical events, such as puncturing, can be considered extreme – or just stupid. If you really want to know what happens when you put a knife into a battery there are plenty of videos on-line that show the result. It appears that many of the current crop of failures are a result of batteries getting hot resulting in an internal failure of insulation and leading to what is often referred to as a thermal runaway. The high energy contained within the battery coupled with the high power capabilities make this quite a spectacular event. So much so that they have been referred to as explosions, even though in reality they are venting / fire events. It is the downside of those long run times and every higher energy batteries consumers demand that have eroded the scope for safe operation.

 
Battery Solutions
Designers have to be aware that the equipment they are working on is safe and fit for purpose. This has to take into account the need for reasonable physical protection, but to protect against someone determined to puncture a battery is clearly not viable. However, the risk of an event leading to an internal failure can be reduced by taking simple measures. As already mentioned, the temporary fix for one problem has been to limit charging once the battery has reached a set percentage of its theoretical maximum charge. This will result in shorter operational run times, but ironically will give the kit much longer overall battery life in terms of the number of charge/discharge cycles that can be achieved.

 
Run Time vs. Battery Life
When looking at new mobile ‘phones, some of the most prominent data presented is in terms of talk & standby time. Consumers are being advised the longer this time the better the device is – trouble is that this is all down to how hard the battery is being worked. Perhaps the figure being promoted should be how many years the battery can be cycled for. As discussed in a previous blog, longer battery calendar life can be achieved by charging to a lower level. So perhaps the answer lies with the marketing teams!

 
Striking a Balance
Battery selection for a new product is much more than headline figures for voltage and capacity. Careful thought needs to be given to the interaction of the battery, the device it is powering, the environment it is operating in and the skill set of the user. The availability of ever more powerful and energetic batteries, and the rules and regulations regarding transport and disposal, mean that battery selection is not as straightforward as seems at first. The use of an independent expert to give guidance to your design team can save a huge amount of time and cost to new project development. If you are interested in finding out more, please contact DM Power Solutions using the contact form on this website.

Costly Mistakes

I see that in the US there is yet another issue with the batteries in self balancing scooters (hoverboards) resulting in a large scale recall, somewhere over 500,000 is a figure being widely banded about. The problem is with scooters made before a new standard was introduced, which seems to be a boost for all those associated with the generation of industry standards.

 
Why the problem with batteries in these particular devices? After all, the technology is in effect the same as that used in your smartphone. Think of all the millions of hours of safe, reliable use the batteries in those devices have clocked up. The reality is that there is a big difference between the single cell battery typically used in smartphones and the multi cell packs designed for other applications.

 
Often it is the way cells are packaged into batteries, and then the enclosure in which they are located, that is overlooked at the design stage. Just assuming that you can link multiple cells into a series and/or parallel arrangements and multiply the cell level performance accordingly is a potential problem in the making. Add to this enclosing the battery in a sealed compartment with little or no air movement, and a high discharge rate, the risk of battery failure rises to a point that is unacceptable.

 
There is nothing inherently wrong with multi cell batteries. Provided the cells chosen are capable of the required discharge rate,  allowances made for de-rating as dictated by the way the battery is housed, a properly designed battery will provide reliable performance over the projected lifetime in a safe and user friendly manner.

 
Expecting your equipment designer to be a battery application expert is a big ask, especially with all the other details that need to be addressed. Having access to an independent battery expert will provide a cost effective solution to help avoid those common, and not so common, battery design and use errors.

 
For more information please email enquiries@dmpowersolutions.co.uk or use the form on the contacts page of this website.

Information Overload!

The day is almost here, it is make your mind up time. June 23rd seemed so far away at the start of the year yet now it is upon us.

It should be simple, only the one question to which you have a binary answer. The only options are ‘0’ or ‘1’. The problem is an almighty bundle of information being thrown out by supporters of whichever side of the argument they are on, often contradictory to what may or may not have been said before. It is inevitable that this information will be skewed in favour of the argument putting it forward, and what is seen as factual by one side is labelled misleading by another. Inevitably the average voter has more of a life to get on with than wading through all the argument and counter argument to come to a reasoned decision. It is difficult to remain balanced and make sure that there is a reasonable equality of both views being received. Everyone will have an opinion based on what the most important factors are to them, sovereignty, economy, immigration, security and so on and there will be a tendency to filter information based on personal importance at the risk of excluding other vital data.

What relevance does this have to a blog on a website about battery selection and design? Well, imagine how much easier it would be to make your referendum choice if you could talk to an expert who has a completely neutral opinion regarding the final result, they just advise on what the right result is for you. Someone that you could talk to about what is important to you and objectively look at what all the options are, and give you a straight, unbiased answer as to what you should logically decide. Then all that time you would have spent researching is yours again, to spend as you see most useful and productive to you.

Selecting the best battery type and configuration is just as complicated, if not more so with various manufacturers and distributors all vying for your business. Plus, with so many variables to consider, the potential to fog the argument concerning a parameter vital to your product is significant. What you need is a truly independent advisor who is working just to your requirements who can give you a straight call on which option is best for you.

Getting an advisor involved is simple and cost effective. Take the next step in selecting the best battery for your project now by filling in the simple contact form on the contacts page of this website, or send an email directly to enquiries@dmpowersolutions.co.uk asking for help.

As for the referendum question, good luck!

Understanding Battery Data Sheets

In the perfect world it would be possible to get all the information you need, and compare different manufacturers product, by referring to their data sheets. But this is not a perfect world, and battery manufacturers seem to have gone out of their way to make it difficult to compare like with like. Even product from the same manufacturer often does not include a consistent presentation of performance across their range of products.

 
If you are looking for general performance guidelines cell and battery data sheets are fine. A lot of effort goes into compiling them and making sure data is accurate. Data is normally presented for stand alone tests, at cell level this means a discharge curve is at a specific current under controlled conditions such as temperature and orientation. The test subject will be a cell that is no more than a couple of months old, and correct test methodology, such as separate current and voltage monitoring connections, will have been implemented. It is also likely that connections to the test cell are through resistance welded tabs, especially for higher current tests.

 
Sometimes there may be some representation of pulse capability, where a higher current pulse is superimposed on a low base load. Again, this is useful general information on how a specific cell will perform, but quite minor changes from the load profile presented are likely to give different results.

 
The use of data presented on charts with logarithmic scales gives the opportunity to present lots of data in a relatively compact form. But as always, the devil is in the detail. Having a chart that shows performance at -20, +20, +40 and +60°C is not much good if you want to know what happens at +5°C. This is a particular problem if you have a high amplitude pulse infrequently applied, you may be able to make a reasonable estimate for what happens to the base load, but the pulse is little more than a guess!

 
And have you ever looked at a cell data sheet where a value for peak current is given in the text, but the charts stop a long way short of showing what actual performance you can expect? These things are often wrapped up in caveats in the small print, involving asking for the manufacturer to evaluate your application on an individual basis. You can be sure that all sorts of detail about how the product will be used will be required such as detailed load definition and environmental temperature profile before any sort of prediction is made. Even then the information the manufacturer provides will be hedged using terms such as ‘expected’ or ‘typical’ performance! And of course they will only tell you the good bits – try and get a cell manufacturer to guarantee the performance figures they give you.

 
This all indicates that the performance shown on data sheets is unlikely to be reproduced in a real world application. If you are trying to decide what cell type, from which manufacturer, you want to use in your new product then relying on data sheets alone is a risky option.

 
Even more risky is using cell data sheets to predict likely performance of a battery made up of multiple cells to give higher voltage, higher capacity batteries. Issues such as localised heating can affect performance considerably. In some cases additional features need to be included in multi cell batteries for safety reasons. When these should be implemented and how they affect to overall battery performance are critical issues. There are so many potential combinations it would not be practical to include these on data sheets, expert advice is a must. Once you have chosen your battery supplier they will of course make sure the product they provide is safe. But if you have done your initial development work based on what you think the voltage output would be, only to find that you need a couple of diodes in the battery, there is a nasty performance shortfall on its way.

 
Experience is key in understanding how data sheet information relates to likely real world performance. Using an expert early in your new product design process to select what cell type, and in what configuration will give the best performance based on a realistic assessment of manufacturers data will help reduce you project risks. If this article has got you thinking, please contact me using the enquiries form on the contacts page of this website. I am always happy to give a no obligation chat through the issues of battery selection and use

Battery Requirements Capture

Battery requirements capture

The important thing about getting what you want is knowing what you want!

All pretty straightforward, and if you are designing a new bit of kit, and want a battery for it, you will probably think a few key performance markers will be all that is required. You would be surprised at how often a battery is specified by voltage alone, or sometimes even just the space envelope. There are occasions where these single main requirements are so important in a design that they swamp the need to examine and specify other parameters. It is all too easy to focus on one design defining factor and lose sight of all the things that go to make up a battery that adds value to a successful design. If your battery falls short of the performance you thought it would give you because of a parameter you had not realised was important, and failed to identify it in your requirements specification (you did prepare one didn’t you?), how do you think the battery supplier will respond when you go back and tell them the battery design they advised you on is not good enough?

It is always worth preparing a requirements specification for the battery. It provides the details of what you need and helps a potential supplier come up with the best power solution for your device. Being able to ask the same question of multiple suppliers will put you in a superior position when choosing who your supplier is going to be. It will also help clarify in your mind what are the must haves are and the performance goals you can be more flexible with. Ultimately the requirements specification will be key in determining which power solution gives the best value.

So what do you need to include in your requirements spec?

This will vary depending on application, and this is where taking on some expert help is advisable if you are unsure. Broadly speaking, the main categories are;

Physical Parameters : Such as dimensions and mass but also electrical connector and case material, especially if not entirely housed within the host equipment.

Electrical Parameters : Basics are the energy required from the battery related to voltage and temperature, power demand also with reference to temperature – but other factors may need inclusion depending on the complexity of the requirement.

Added Features : Such as state of health & state of charge information and how this is displayed to the user.

Environmental: Vibration, shock, acceleration, immersion are examples of things that may need to be considered. In some cases electro magnetic compatibility may need consideration.

Safety : Certain applications may require a battery that is designed with added layers of safety. Protection against inadvertent charging, especially if there is both a rechargeable and non-rechargeable battery option for the equipment. These are examples of things that require addressing at the battery design stage.

Operational Use : Will the battery be stored for lengthy periods of time when not in use? If so, under what conditions? If the battery is going to be stored for many years, what are the minimum performance requirements?

Transportation : Certain types of battery have restrictions placed on them regarding methods of transportation as well as added regulation. Knowing that frequent movement by air (for example) is required, enables the battery designer address this avoiding potential delays and extra costs later.

Through Life Issues : Equipment disposal and obsolescence management for example.

As well as a section covering specifics relating to your project!

 

Information under each heading above is only an indication of the type of data required, and for some parameters can be quite complex. Of course there may be no specific requirement for some of these categories at all, just asking yourself the question is sometimes enough to know it has been addressed. The difficulty is knowing when the information you think is irrelevant is actually quite important to battery function, for example if a particular cell type behaves differently depending on its orientation. In this case if you know that your kit is required to be used for long periods of time inverted, there may be some cell types that are unsuitable!

If this seems a bit daunting, don’t panic. Enlisting the help of an independent battery expert who can guide you through the creation of a battery requirements specification will enable you to address those categories that need inclusion whilst omitting those that don’t. The result – cost effective battery selection and a gold star for battery selection!

For further information please contact me at enquiries@dmpowersolutions.co.uk or use the contact form on the website.

 

Do You Really Need Hi-Tech Batteries?

Is a Hi-Tech battery right for you?
An area that I think is often overlooked is the detailed selection of the battery to power equipment, or more precisely, the chemistry of the battery. There is the understandable pressure to select a battery that has an image in keeping with the hi-tech nature of the equipment it is intended to power. This tends to lure designers into selecting a lithium battery because of the draw and aura of having a battery perceived as hi-tech, no doubt with a little persuasion from a marketing angle too!

Making the right battery choice
Is the tendency to specify a lithium battery founded on good judgement and fact? As with most things there are pros and cons with whatever approach is taken. Sometimes the choice may not even rest with the battery performance alone, weight volume and even ease of transport are examples of factors that need to be considered. Additionally, variations in the way different battery types respond to increased loads and the operating temperature will mean that a battery that seems ideal at one end of the performance envelope is woefully inadequate at the other.

Key Parameters Check
As a quick comparison I have looked at three different primary (non-rechargeable) battery chemistries across a range of parameters, comparisons based on the same cell size.
Cell Type A
Highest energy cell
Best Operating Temperature Range
Poor rate capability (typically a few 10’s of mA, low 100’s under favourable conditions)
Start up delay needs managing in certain applications
Cell Type B
Highest Power Density
Good operating temperature range
High discharge currents (Amps) maintained down to -30°C
Minimal start up delay
High cost
Cell Type C – Low tech option
Significantly lower cost (around 20% of Type A)
No Transportation Issues
No ‘start up’ delay
Good rate capability (100’s of mA)
Low energy density
Not much performance below -5°C

Even from this relatively short comparison it can be seen that if weight and volume are not a problem, but cost and transportation are, the ‘low tech’ route really is worth considering.

Taking the correct guidance
Of course in a short blog like this it would be difficult to examine all the performance levels and present them clearly. Each new design will have its own key drivers which may push the battery selection in a different direction. That is why it is vitally important to capture all the requirements that the battery will need to meet in your design, prioritise these, and then match different battery types to them. Calling on the expertise offered by an independent expert who can examine options from a wide variety of sources, can ultimately save you time and money in your new development process.

New Year, Same Old Battery Headlines!

 

 

Looking into the battery future

I do not need a crystal ball to know battery related headlines that will be hitting our screens during the coming year: ‘Get More From Your Battery’, ‘New Battery Charges to 85% in ¼hr Using Renewables’, ’Breakthrough in Extended Battery Life’ or ‘WizzoXzX Hampered by Poor Battery Performance’, ‘User Arrested for Stealing Electricity to Charge Phone’, or a combination and variation on these themes.

Attention Grabbing

You cannot really blame the headline writers, these are the problems that have been associated with battery powered portable equipment right from the start. Yes, they grab the attention of the reader, but it is rare to find an article that really justifies the headline. Too often the article is a recycling of already established ideas, or a research programme that will take many years before it escapes the development laboratory.

 Battery Example

Only a couple of days into the new working year I had a contact email me an article asking for my opinion on its contents. ‘New (kit) charges internal battery to 80% capacity in <½Hr from built in solar panels’ the headline proclaimed. Now that is a headline that does nothing for me, 80% of what? Although a theoretical run time for the kit was given, this was presented in a way the suggested that this was from an add-on external pack. The problem with the article was that no details about the capacity of the internal battery was given. And this was without considering environmental conditions

Battery Charge Efficiency, Nothing New

The reality of the article was that it was not reporting on a new technology breakthrough. In practice even old generation Lithium Ion and derivative type cells/batteries have very good charge acceptance figures, typically 90 to 95% especially during the early phase of charging. If you are charging a small lithium ion cell with a capacity of a 200mAh, charging to 80% capacity is 160mAh. Allowing for typical charge acceptance efficiency, this battery will only need a 1.5W output solar panel (approx. 120cm²) to charge as per the headline, hardly ground breaking!

It is not about the battery

This example shows up the real problem, it is not about the battery but rather how it is used and specified. Imagine how efficient your car engine would be if the available energy from the fuel you put in was 90% plus! Your typical Lithium Ion cell with and in/out efficiency at this level is clearly not the problem. Even if a new technology battery appeared that could take charge faster, or doubled the capacity in the same space, the limit would still be the provision of sufficient energy and power to charge in the specified time.

My Verdict

After all was said and done, I reported back to my contact that there was nothing wrong with the article, it was just that it did not really tell  anything that was not already known. There was no magic, no technology breakthrough, just a lithium ion cell doing what it does best – accepting charge efficiently!

Battery Power Solutions

This example shows how it is important to look behind the headlines. The headlines may look enticing, but there is no substitute to having someone who knows the battery world inside out to advise you on your battery power source solution.

 

Taking Ownership of Your Battery!

The thing about batteries is that there is never one that quite gives you enough power/energy in the form factor you want. It all seems so simple, identify an ‘AA’ cell and allocate the right space and holder for it: simple! But your design has evolved, you need more voltage, more capacity and a bit more power, nothing quite seems to fit the bill. This situation seems to always occur for that big, prestige job. The big, one off buy’ project for a blue chip client. So your search is on, how do you get the voltage/capacity/power combination you need? Time to look at having a bespoke battery designed! There are so many different cell sizes and chemistries that can be used in various series and parallel combinations that it can seem like doing a jigsaw puzzle without knowing what the end result will look like. And what about those extra goodies that look so good in the electronics press, some capacity gauging perhaps, state of health monitoring, communications? Then there are the additional bits that go into the battery to make sure it can operate safely, what effect do these have on overall performance? Oh, and how is it going to be housed, in a rigid case or a ‘softpack’ built into the main equipment? Plus considerations for the environment it is going to be used in, end user industry specific requirements, transportation, the list of considerations seems endless. Your hunt is on for a supplier, and there are lots around. The chances are that they will tell you not to worry, they will do all the work for you and you will get a shiny new battery with everything sorted out. The problem is you will have lost control, even if you make sure you select a supplier using ‘industry standard’ cells in the design. At first this does not seem to be a problem, it is a few years later when there is a need for the kit to be produced again for a new ‘one off’ order that the troubles start. Yes, you may have chosen industry standard cells, but the original supplier no longer produces them. Fine, you will find another source, but then you find that there is a little special ‘tweak’ in the battery designed to give you the best performance that is proprietary to the original battery supplier. They will not produce it for a third party, and they will not license the design to you. You are faced with finding another supplier to produce an equivalent design from scratch. So now your original budget for this new ‘one off’ order has gone out of the window because you need to pay for another new battery development programme along with re-qualification and generation of new support documentation. This is why it is advisable to make sure you keep full design rights over the bespoke battery for your fabulous new bit of kit, and the easiest way to do that is to keep ownership of the design. If you do not have the in house capability to do this it is a simple task to bring someone in to help your design team through the process. The use of a battery application and design consultant will help you keep ownership of your design, giving you the assurance that the job has been done properly and will not leave you with an unnecessary obsolescence problem later.

Lithium Primary Batteries: Managing Passivation

Passivation, friend or foe?

One of the issues I am most frequently asked about by equipment designers is passivation in liquid cathode lithium primary cells and batteries. Questions regarding ‘avoiding’ or ‘preventing’ passivation are not uncommon, but the hard truth is that these cells types would not be practical without passivation. The high energy densities possible with the liquid cathode cell design are very appealing to equipment designers, with the added benefits of a wide operating temperature range and long shelf life. Depending on the precise chemistry and cell construction, reasonable (for a primary cell) power is achievable too. Now long established in the market place, with a good safety and reliability reputation, liquid cathode lithium primary cells are often the first choice power source for portable powered equipment. The drawback is the problems associated with a slow start up, sleepy cells with lower than expected voltages when power is demanded from them.

Overview of Passivation

At the surface of the lithium anode a cell, not under load, will form an insulating layer, known as the passivation layer. This is vital as without it the ‘liquid cathode’, present throughout the cell, would be in permanent contact with the lithium resulting in a continuous discharge. Obviously disastrous for cell life! A very small amount of active material in the cell is used up during the formation of this layer, which starts to form as soon as the cell is ‘filled’ during manufacture. As conditions at this stage are reasonably controlled, in terms of material age, temperature and so on, the characteristics of the passivation layer in a new, unused cell, are well understood.

What does it mean to the user?

When the cell is first required to provide energy to the equipment, this passivation layer needs to be broken down to allow the lithium to be accessed. At first application of the load this manifests itself as a drop in voltage for a few milliseconds before recovering to the expected level. Depending on the amplitude of the load, and other factors such as temperature, this voltage drop can be significant resulting in a voltage level below that at which the host equipment can operate. Heavy initial loading can also extend this low voltage period leading to users thinking the battery has failed. A cell that has gone through this voltage dip is described as de-passivated.

Partial Discharge.

As soon as the external load is removed, the passivation layer starts to re-form. The nature of this re-formed passivation layer will now be dependent on other factors, such as cell age, state of charge, usage pattern, and most importantly temperature. A very small amount of capacity will, again, be used in re-forming the passivation layer, as it will each time the cell is partially discharged.

Management

Avoidance and prevention are not options (sorry), but with correct management passivation should not be an issue. Introducing de-passivation routines into equipment start up procedures is a good start, but the passivation layer will have different characteristics each time it re-forms and so the same routine may not work every time. Another approach is to draw a continuous low current from the cell, just enough to keep the passivation layer in a state that is easily, and quickly, broken down. This is a particularly useful method where sudden higher power, short duration, burst are required. The downside being that energy is being continuously drawn from the cell, and it is likely that the higher the power burst, the higher the background current will need to be. More complex load profiles, and very long operational life (15 years+ claimed), all bring their own challenges to cell management.

Summary

Of course it may be that in managing passivation, the advantages in using liquid cathode cells and batteries is lost. Knowing what you need your battery to do at the outset helps in producing a reliable product with the most appropriate power solution. There are many different cell and battery types to choose from, but making sure you find the best match for your design is more difficult than many think. Designing equipment to make the most of the battery, rather than choosing a battery once the equipment is designed, will give the equipment a better power solution.