Electrical Lifepo4 Battery Replacement

blackstangt · Oct 17, 2014

Looking to reduce weight a bit, I found some Lithium Iron Phosphate batteries with high CCA ratings. The difference in weight between them and my current battery is about 35lb. They can handle being charged by automotive alternators and temperatures down to -30C. The chemistry is safe and the cells are balanced.

Reasons for this option:
-35 lb
no extra weight from battery box and wiring
cost is about the same as some expensive lead batteries
provides low voltage kill switch - battery never dies
battery died while I was away

I'm trying to find out if there are potential problems with this setup, so that I can resolve them before use. The batteries have relatively low Ah ratings, but don't lose Voltage when drained like a lead acid battery.

I haven't seen anything on most car forums about lithium starting batteries, so I'll be testing it in the garage over the winter and posting my results.

Source:

http://store.starkpower.com/-ULTRA-START-Voltage-Cut-off-and-Cell-Balancer_c_28.html

stykthyn · Oct 18, 2014

A little curious. Price seems reasonable enough.

Noobz347 · Oct 18, 2014

There was a guy here at one point that was using those.

What I remember was an ORANGE engine bay. Everything had it's place/immaculate.

Does anyone else recall the photos that I'm talking about? One of his threads talked about the batteries.

Was it the dude with the Kenne Bell air-to-air intercooler?

Noobz347 · Oct 18, 2014

Aha!

View attachment 110447

It's from this post here:

http://www.stangnet.com/mustang-for...nne-bell-for-92-lx.783231/page-9#post-8414239

You could probably ask him anything about that battery. They're different brands but I think the same style. Can be mounted upside down even.

jrichker · Oct 18, 2014

Li-P batteries have a different charging curve from the OEM lead -acid batteries. If they overcharge, they overheat and catch fire. Google Boeing and the 787 Dreamliner - the battery problems grounded entire fleets of brand new 787 aircraft, costing millions of $$$ in lost revenue and expense to find and fix the problem.

blackstangt · Oct 18, 2014

Fortunately, I'm not dealing with the low pressure, low temperature situation seen at altitude, and they're a different chemistry.
LiFePo4 are the safest:
http://batteryuniversity.com/learn/...ons_for_the_battery_problem_on_the_boeing_787

I am a little concerned with overvoltage. If the alternator voltage regulator failed, an overvoltage situation could occur, damaging the battery. This is possible on a lead acid battery as well, but there are many ways to back up the voltage regulator to ensure the voltage stays low enough.

blackstangt · Oct 18, 2014

That is really nice, noobz347. That's an odyssey battery, which saves a bit of weight as well, but is still lead acid.

blackstangt · Oct 18, 2014

The battery shipped today.

blackstangt · Oct 24, 2014

1.56 lb battery started the car easily on less than a full charge (13.3 out of 14.4 Volts).

Voltage from the alternator was a little high, so I am going to add either a zener diode to reduce it, or a better regulator. The alternator is 7 years old.

http://imgur.com/a/wRVy3#0

Noobz347 · Oct 24, 2014

If looking for do-it-ur-self:

http://www.maximintegrated.com/en/app-notes/index.mvp/id/760

7991LXnSHO · Oct 25, 2014

Keep us informed and for sure let us know if the battery goes Boeing/Tesla. Even Optima batteries have a learning curve, so this new tech should have some precautions to learn too.
How about some more info on how you are using a Zener diode (and what it is I bet for most readers).

7991LXnSHO · Oct 25, 2014

Your article says the battery requires a different charger setting than other lithium batteries. I wonder how the automotive charging system meets its needs. A lead acid battery is surprisingly forgiving to charging rate, as long as you do not ignite its flammable gasses or block its vents.

jrichker · Oct 26, 2014

blackstangt said:
1.56 lb battery started the car easily on less than a full charge (13.3 out of 14.4 Volts).

Voltage from the alternator was a little high, so I am going to add either a zener diode to reduce it, or a better regulator. The alternator is 7 years old.

http://imgur.com/a/wRVy3#0

A zener diode absorbs or clamps the excess voltage that is placed across it. You are proposing using a zener diode as a shut regulator, which it will do. however there are some limitations.
If you clamp the voltage at 14.2 volts and the alternator puts out 15.2 volts at 130 amps, you need a zener diode that will dissipate 130 watts of excess energy.

W=I x E , 1 volt x 130 amps = 130 watts

Finding a zener diode that that large could be very expensive, not to mention what sort of load the clamp effect would place on the alternator. The alternator regulator circuit will attempt to increase the voltage output back to it's set point, which in this example is 15.2 volts

See http://en.wikipedia.org/wiki/Zener_diode to figure out the details.

7991LXnSHO · Oct 26, 2014

I was thinking it was a darn big diode, but did not think about how it might act like a short on the alternator. A really good voltage regulator might be cheaper.

blackstangt · Oct 26, 2014

The included charger goes up to 14.6V, which is the maximum charge a lead acid battery should receive also. My stock output (65-75 amp) alternator was putting out its maximum of 14.8V immediately after starting the car for the first time in 3 months, but most likely because the voltage regulator is worn out. I plan on upgrading the alternator anyway, my lights dim at low RPM. I don't think 14.8V will damage it and I expect a 15v diode will protect it.

These are about a dollar and designed for this type of automotive use:
http://www.littelfuse.com/products/...-and-high-reliability-tvs/tpsmd/tpsmd15a.aspx

I'm doing some other work to the car, so I can take my time finding a solution.

blackstangt · Oct 26, 2014

Another manufacturer that has built in overcharging protection:
http://earthxmotorsports.com/our-batteries/#charging

jrichker · Oct 27, 2014

blackstangt said:
The included charger goes up to 14.6V, which is the maximum charge a lead acid battery should receive also. My stock output (65-75 amp) alternator was putting out its maximum of 14.8V immediately after starting the car for the first time in 3 months, but most likely because the voltage regulator is worn out. I plan on upgrading the alternator anyway, my lights dim at low RPM. I don't think 14.8V will damage it and I expect a 15v diode will protect it.

These are about a dollar and designed for this type of automotive use:
http://www.littelfuse.com/products/...-and-high-reliability-tvs/tpsmd/tpsmd15a.aspx

I'm doing some other work to the car, so I can take my time finding a solution.

That Littlefuse device is meant to clamp voltage spikes that last no more than a few thousands of a second. It is not designed to continuously clamp voltage, and acts like a dead short across power and ground. That's not a workable solution for what you are trying to do.

blackstangt · Oct 27, 2014

You're right, I overlooked that, a Zener diode is still a better option. The battery should be OK as long as it isn't charged over 14.6 Volts, so a voltage regulator that works properly shouldn't ever cause over-charging. However, I want to have some insurance to assure it doesn't happen.

jrichker · Oct 27, 2014

How's your understanding of Ohm's law and basic electrical theory? It sounds like you are in over your head.

It seems that you missed the fact that with a zener operating as shunt regulator, you must absorb all the excess power above the zener's breakdown voltage. The zener diode absorbs that power, and the power is high in your proposed idea: Votls x Amps = Watts or power. Finding a zener diode with a power rating of more than 50 watts is going to be difficult and expensive.

How many ohms of resistance is the resistor that the zener needs to work with? You need to know the zener voltage and the max amount of current you want to pass through it in order to calculate the resistor value.

If you use a power mosfet in conjunction with a zener diode to make your shunt regulator, you still have to dissipate large amounts of lR energy in the form of heat. That means a large heatsink and a big, low resistance, high wattage resistor >150 watts.

blackstangt · Oct 27, 2014

I'm trying to find a solution that could be applied to any mustang (or every car in general) without requiring excessive wiring and prevent over-voltage for any type of battery/system. I don't need a basic electrical theory lesson. I have a decent knowledge base, but I haven't seen everything and am looking for a product that will fulfill the intent in the simplest configuration.

I must emphasize that a LiFePO4 battery is safer than lead acid, over-voltage will not cause acid to spill or explode all over the engine bay like a lead acid battery could. At a higher voltage than a lead acid battery could handle (less than 18v), it would smoke and fizzle, not explode.

LiFePO4

View: https://www.youtube.com/watch?v=gpMRYJdzbnI

View: https://www.youtube.com/watch?v=EMARDvMz62A

Lead Acid

View: https://www.youtube.com/watch?v=d_TnsHu2u4c

Can you think of a simple way of backing up the alternator's voltage regulator, to prevent over-voltage?

Electrical Lifepo4 Battery Replacement

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