# LiFePO4 Performance and Safety FAQ



## shizzzon (Dec 7, 2014)

I am involved in the hobby and business of car audio competition and the current market is looking to offer LiFePO4 as a choice for supporting enormous power output in vehicles that cannot fit large amounts of alternators.

For example- over 100,000w

Because of weight savings, enormous burst potential, etc, these look to be preferred.

But, i can't find answers to may things we are curious on and this forum looks to be the best to ask these questions.

I would also like to say one company is about to release their own version soon and limited safety information has ever been talked about.

*Here are my questions\concerns-*


Most cells i see are only rated to about 125F and never below 0F.
*How will these cells ever work in a vehicle where we experience 90F+ and Below 0F weather?* The summer weather will scorch the inside temperature of the vehicle.

Charging-
Vehicles typically only charge to 13.8v(on 12v).
We were told that is fine as longer life will be seen by not fully charging packs at 14.6v.

*How does cell balancing work on an alternator in this aspect?*
From what i understand, balancers work when bank is charged to it's fullest capability based on charge voltage then voltage removed, correct?
If true, this would simply mean turning car off.

I'm just extremely leary about cell imbalancing.



Now, we are looking into high voltage usage for this cell technology-
Approximately 64 cells in series.

This is to be used with advanced amplifiers which run up to 50,000w per device.

*Anyways, when building yourself, where do we source our PCBs through?*
We cannot find any 200+v pcbs for high current.

We currently are looking at 2 cells for use-

Headway 38120HPs or A123 26650s
In the following combinations-

Headway- 68s3p (for 350A bursts)
A123 26550- 68s4p (for 350A bursts)

They would only ever see an actual charger in between shows as normal driving would rely on alternator.

For high voltage, we have a supplier who can build us 
12v to ~118v DC output around 12A per converter.

Based on alternator limitation, we would just get 2 of them and put them on each set of 34 cells in series.

*I do not know if we can still run just a single large PCB or multiple 
required?*

The aH ratings between the 2 cells are decently matched to the alternator's ability and burst power is only used for 4seconds at a show.

The main reason we are looking into high voltage is because the cost of the amplifiers are more than half the cost of the 12v models including the cost of the DC boost converters.


I have been doing some research but do not feel confident enough to start communicating with A123 and batteryspace about our usage and PCB manufacturing just yet until we know everything about the technology based on our needs.


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## major (Apr 4, 2008)

Hi shizzzon,

The obvious solution is to use your EV's high voltage propulsion battery to power the audio system. They are safe battery systems and perform over the required environmental conditions. 

Welcome to the DIY Electric Car forum.


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## shizzzon (Dec 7, 2014)

Thanks for replying but this is not an EV!

These applications are purely for gas powered passenger vehicles.

We are used to hauling around up to 1000lbs of AGM batteries but we are looking to change that by switching to LiFePO4 technology so we can install even more power in these vehicles.

The only power source is the alternator and the batteries we build.


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## PStechPaul (May 1, 2012)

I hope you realize that 100,000 watts of audio in a sealed chamber the size of a car will likely produce lethal levels of sound pressure. I don't really know anything about car audio competition, or care to learn, but here is a start:
http://www.caraudiohelp.com/car_audio_competition.html


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## shizzzon (Dec 7, 2014)

PStechPaul said:


> I hope you realize that 100,000 watts of audio in a sealed chamber the size of a car will likely produce lethal levels of sound pressure. I don't really know anything about car audio competition, or care to learn, but here is a start:
> http://www.caraudiohelp.com/car_audio_competition.html


I appreciate your concern but this isn't about the car audio side of it.. 

That would be a discussion that would go WAY off topic here.. 

I am a distributor and work with a couple engineers that work in the car audio hobby.

We are experienced and well aware of Dbs.

We build setups up to 168db for daily driving and up to 185db for extreme competition.

None of this we are actually IN. 

Some vehicles run over 1,000,000 watts but this isn't tailored toward those.

We are primarily gathering information on LiFePO4 technology in it's safety ratings.


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## Hollie Maea (Dec 9, 2009)

Maybe I'm misunderstanding something here, but how are you planning on charging a 68 series string with a 13.8V alternator?


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## shizzzon (Dec 7, 2014)

Hollie Maea said:


> Maybe I'm misunderstanding something here, but how are you planning on charging a 68 series string with a 13.8V alternator?


As stated before-

"*For high voltage, we have a supplier who can build us 
12v to ~118v DC output around 12A per converter.

Based on alternator limitation, we would just get 2 of them and put them on each set of 34 cells in series.*"

We would have to use each converter per half the series capacity..


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## PStechPaul (May 1, 2012)

Most automotive alternators are capable of not much more than 100A at 12V, although it might be possible to tweak the regulator to get higher voltage at high RPM. If you are using two boost converters with nominal 12V input and 118V at 12A output, you'd need 118A input, which may be possible, but it's still just about 1500W each, or 3000W total. If you are looking at 100kW, are you planning on doing that for just a few minutes, or an hour or longer? For 10 minutes, it would be about 16 kWh, and about 6 hours of driving to charge the pack. I see that you only need such high power for about 4 seconds so you could get by with as little as 112 Wh. 

At 64*3.2=205V, 100kW is 488 amps. A 50 A-h pack should be able to handle this at 20C, and would be about 10 kWh. At about $400/kWh you'd have about $4000 in batteries. You could make sure the cells were reasonably well balanced in terms of capacity and charge them only to about 80% and discharge no lower than 20%, which might not even require a BMS or charge balancer. You could just check them occasionally and adjust them for approximately equal SOC, and use the full pack voltage as the max/min points. With a good Ampere-hour meter, you can just use a constant current over a specified time, or if the charging is not constant, just calculate the energy based on frequent samples.

As for a PCB that will handle 200V, that is well within the capability of any professional PCB manufacturer, and some can supply heavy weight copper (4 ounce rather than standard 1 ounce) for a moderate extra charge, if you want to carry high current. I advised Valery to contact www.eiconnect.com or www.zoompcb.com and he is using them for his 12 kW chargers (see that thread). But I'm not sure why you need a custom PCB. There are many BMS systems that can handle battery packs upwards of 300 volts, and you don't need anything very sophisticated to control charging and monitor cells to very safe conservative limits.

Also, you can get 24V high power truck/RV alternators, and automotive inverters with 24V input and 1000 to 6000 watts output at 220 VAC, which are about 260 VDC internally. I have some 1000-1500W inverters that cost well under $100 each.


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## shizzzon (Dec 7, 2014)

PStechPaul said:


> Most automotive alternators are capable of not much more than 100A at 12V, although it might be possible to tweak the regulator to get higher voltage at high RPM. If you are using two boost converters with nominal 12V input and 118V at 12A output, you'd need 118A input, which may be possible, but it's still just about 1500W each, or 3000W total. If you are looking at 100kW, are you planning on doing that for just a few minutes, or an hour or longer? For 10 minutes, it would be about 16 kWh, and about 6 hours of driving to charge the pack. I see that you only need such high power for about 4 seconds so you could get by with as little as 112 Wh.
> 
> At 64*3.2=205V, 100kW is 488 amps. A 50 A-h pack should be able to handle this at 20C, and would be about 10 kWh. At about $400/kWh you'd have about $4000 in batteries. You could make sure the cells were reasonably well balanced in terms of capacity and charge them only to about 80% and discharge no lower than 20%, which might not even require a BMS or charge balancer. You could just check them occasionally and adjust them for approximately equal SOC, and use the full pack voltage as the max/min points. With a good Ampere-hour meter, you can just use a constant current over a specified time, or if the charging is not constant, just calculate the energy based on frequent samples.
> 
> ...


Thank you for the info.

I have a single 270A alt with custom thermal protected regulator from rectifier abuse. 

I'm used to running 10-25kw setups in the past with single alternator.
Just have shorter play time as you stated.

The statement as there readily available BMS up to 300v, etc.. Show me please! I haven't found any and have also never heard of those PCB sources in which i will research soon as well.

Remember this-

In my application, i'm eyeing low aH but large burst potential due to limitations of charging potential.

This is why i'm staying close to 3kw of charging(from the converters).
Burst potential could be 1 trillion watts.. Don't need that, heh, but just to give example that i can control continuous usage easy by listening pleasure. 

I'm just more curious on handling burst potential for short period.


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## PStechPaul (May 1, 2012)

One of the PCB links was wrong. It should be http://www.eiconnect.com/.

The units I have looked at are the mini-BMS which is one PCB per cell and unlimited cells, for about $13 each:
http://www.electriccarpartscompany....-House-Power-Board-br-Cell-Modules_p_107.html

Here is another one:
http://www.electriccarpartscompany....Battery-Voltage-Amperage-Balancers_p_320.html

A comparison of various types:
http://liionbms.com/php/bms_options.php

There are several threads in this forum for various designs for BMS systems. I have a couple of designs partially done but have not decided on a final version to build and test. 

For your very high current short time applications you might want to go with Li-Ion or Li-Poly cells which are rated as high as 50-100C. They are cheaper but have some safety concerns that are more severe than the LiFePO4, but there are ways to protect against catastrophic failure and runaway multiple-cell situations. Check out some of the hobby sources for pouch cells. Here is a list of some sources:
http://liionbms.com/php/cells.php

I have dealt with Hobby King for some cells and other devices:
http://www.hobbyking.com/hobbyking/store/lithium_polymer_battery_configuration.asp

Here is a 6.6 A-h 90C 2S2P (7.4V) pack for about $60 each:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=63005

30 pieces would be $1800 and should give you a burst of almost 600 amps at 200 volts or 120 kW!


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## major (Apr 4, 2008)

shizzzon said:


> Thanks for replying but this is not an EV!
> 
> These applications are purely for gas powered passenger vehicles.


That was my point. Not an EV. Gas burner. Wrong place. Also, a business. Not DIY. Wrong place. Just a distraction for us, IMO. In fact, you want to use our resources to burn even more fossil fuel and pollute our environment not only with chemicals but noise as well.


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## lithiumlogic (Aug 24, 2011)

shizzzon said:


> *Most cells i see are only rated to about 125F and never below 0F.
> How will these cells ever work in a vehicle where we experience 90F+ and Below 0F weather?*
> 
> The cells don't mind being frozen so long as they are not charging at that point. If the electrolyte is frozen then the lithium ions can't penetrate the anode / cathode materials and end up electroplating on the surface as lithium metal. This causes permanent capacity loss, and is also a safety risk. It should be quite easy to inhibit charging below 0C?
> ...


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## shizzzon (Dec 7, 2014)

major said:


> That was my point. Not an EV. Gas burner. Wrong place. Also, a business. Not DIY. Wrong place. Just a distraction for us, IMO. In fact, you want to use our resources to burn even more fossil fuel and pollute our environment not only with chemicals but noise as well.


Your resources? I didn't know you owned this website.

I'm using your resources to burn fossil fuel and pollute environment?

Well, i guess our country should research EV tech.. 

Oh wait.. you do NOT want us too because of your arrogance so we'll just keep burning since you do not like us.

And what does being a business have anything to do with this topic?

This IS DIY. This isn't for resale.. 
Perhaps if you quit assuming every single part of my posts and help like i applaud others for, your "resources" and your "environment" wouldn't be burned by this fossil fuel you look at as evil. 

And you do not like noise either?
Sounds like you forgot to have fun. Sad really.


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## shizzzon (Dec 7, 2014)

lithiumlogic said:


> shizzzon said:
> 
> 
> > *Most cells i see are only rated to about 125F and never below 0F.
> ...


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## lithiumlogic (Aug 24, 2011)

shizzzon said:


> lithiumlogic said:
> 
> 
> > Heat would be from cabin temperature. Up to 150F is common here.
> ...


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