Drop-in car battery DIY?

[danroonie]

I have a DIY 12V lithium LiFePO4 battery. Is there anything electrically that would prevent me from installing it with an Overkill BMS into a 2019 Pacifica PHEV as a drop in replacement to its aging gel start-stop battery? The existing battery is H7 Group Size 650 CCA Fox Type F fox top terminal connector. Battleborn advertises a drop in battery but at 100ah it's pricey at >$900 and I'd like 200 ah.

Battleborn's BMS features:

1. High Voltage Disconnect (> 14.7V)
2. Low-Voltage Disconnect (< 10.6V)
3. High Temperature Charging and Discharging < 131°F.
4. Low Temperature Charging < 25°F
5. High Current Discharge Surges current < 100 Amps (+/- 5%) < 30s, or anything larger for 0.5s. Short Current Discharge Surges via short circuit protection.
6. Passive Load Balancing of Cells

 

[SamDeleted]

I think the start motor will draw more current than the lifepo4 can handle

 

[justinm001]

You're trying to replace a 650cca battery with a 100a battery? Plus the alternator doesn't have a lithium charging profile. Bad idea

 

[usherben]

I have the same vehicle (2017). As this this the PHEV version, there is no traditional starter or alternator.
The engine is started by the high voltage traction pack and the 12V battery is topped up by a DC to DC converter.
I'm not sure if this would work, but I think it would.

 

[meetyg]

Not a good idea, unless you have some way of controlling the charge current to the Lifepo4. Whether it's an alternator or DC-DC doesn't matter much, as a Lifepo4 battery will pull alot of amps (even more than thier capacity, because of low internal resistance) from either one, because they are both designed for SLA batteries. Lithium chemistry needs a constant-current / constant voltage charge profile.
Most alternators and DC-DC chargers (onboard vehicles), are constant voltage.
So in short, you will stress you alternator/DC-DC and the Lifepo4 battery.

Also, low temp charging is not recommended for Lithium as it can damage the cells. You need to control that too.

As is mentioned here on the forum many times, the BMS is the last means of protection and should NOT be used to control charging.

 

[Sean Very North]

As is mentioned here on the forum many times, the BMS is the last means of protection and should NOT be used to control charging.

This is just your opinion, I believe the opposite to be true, but I suppose it'll depend if you trust your BMS.

 

[danroonie]

Battleborn doesn't mention any issues with using their's as a drop in and their warrantee is 10 yrs:

but wouldn't want to stress the Pacifica's DC-DC charging system. It does seem silly to have a 12V Gel battery 2 feet next to a 12V lifepo4 battery.

 

[meetyg]

This is just your opinion, I believe the opposite to be true, but I suppose it'll depend if you trust your BMS.

Thus is my opinion and just about most of the forum which is more solar/battery/DIY educated than me...
I came to the forum to learn from other's experience and mistakes.

 

[Ruff]

If the under hood temp is not too high, you could use one of these H7 batteries. I put an H5 in my MINI Cooper S and have had good results this year. (I choose this because the car sits in the garage more than it is driven, did not want to install a battery maintainer).

 

[HRTKD]

This is just your opinion, I believe the opposite to be true, but I suppose it'll depend if you trust your BMS.

I think there is overwhelming concurrence that the BMS is to be your last defense. All charging devices should be configured so that the BMS almost never has to step to stop a charge (or discharge).

One of the EV manufacturers is now (or plans to) use LiFePO4 as the 12 volt accessory battery. That's great. Less weight, probably a longer life. But that car is configured to charge a LiFePO4 12 volt battery and most EV's are not.

 

[meetyg]

I think there is overwhelming concurrence that the BMS is to be your last defense. All charging devices should be configured so that the BMS almost never has to step to stop a charge (or discharge).

One of the EV manufacturers is now (or plans to) use LiFePO4 as the 12 volt accessory battery. That's great. Less weight, probably a longer life. But that car is configured to charge a LiFePO4 12 volt battery and most EV's are not.

Which manufacturer is that?

 

[sunshine_eggo]

Battleborn doesn't mention any issues with using their's as a drop in and their warrantee is 10 yrs:

but wouldn't want to stress the Pacifica's DC-DC charging system. It does seem silly to have a 12V Gel battery 2 feet next to a 12V lifepo4 battery.

Explore their site. Nowhere do they discuss use as starter batteries - only as power system batteries.

Call them 855-292-2831 and get back with us.

There are dedicated high amperage LFP starter batteries, but they are very expensive primarily for their ability to output notably higher currents due to the use of high C rate cells.

 

[HRTKD]

Which manufacturer is that?

I can't find the article now. Sorry.

 

[sunshine_eggo]

This is just your opinion, I believe the opposite to be true, but I suppose it'll depend if you trust your BMS.

Have you happened to catch the times on this site where someone's BMS was either intentionally or unintentionally used as charge cut-off, racking up 100s or 1000s of protection events and causing the FETs to fail short circuit? I have.

I spent ~$1000 on my BMS, and I mostly trust it because it's actually controlling my system - telling my charger what voltage and what current to use and signalling them directly to stop inverting or charging manually rather than just disconnecting a relay/opening a FET.

 

[Nobodybusiness]

This is just your opinion, I believe the opposite to be true, but I suppose it'll depend if you trust your BMS.

You really got to trust your BMS.
I don’t know anyone that trust their BMS that much
Especially the FET ones.
Contactor one maybe.

 

[Sean Very North]

I think there is overwhelming concurrence that the BMS is to be your last defense. All charging devices should be configured so that the BMS almost never has to step to stop a charge (or discharge).

One of the EV manufacturers is now (or plans to) use LiFePO4 as the 12 volt accessory battery. That's great. Less weight, probably a longer life. But that car is configured to charge a LiFePO4 12 volt battery and most EV's are not.

I think there is overwhelming use on this site of cheap, bug ridden management systems that aren't reliable, hence the general agreement that multiple lines in the sand need to be present.

 

[Sean Very North]

Have you happened to catch the times on this site where someone's BMS was either intentionally or unintentionally used as charge cut-off, racking up 100s or 1000s of protection events and causing the FETs to fail short circuit? I have.

I spent ~$1000 on my BMS, and I mostly trust it because it's actually controlling my system - telling my charger what voltage and what current to use and signalling them directly to stop inverting or charging manually rather than just disconnecting a relay/opening a FET.

I agree completely, I've got numerous Batrium systems running, it took me a while to trust them, especially given how problematic their support was, but that's back maybe five years, I absolutely trust them now. Similar with all of the other quality management systems that we've used 100s of, but you do tend to get what you pay for, so I completely understand why folks using the cheapest BMS they can find, using series FETS as a means of interruption are cautious about relying on it for the subtle aspects of energy storage system control, but I feel their experience and opinion is biased due to their lack of knowledge of how dependable a quality system can be.

Just my experience based opinion.

 

[Nobodybusiness]

I agree completely, I've got numerous Batrium systems running, it took me a while to trust them, especially given how problematic their support was, but that's back maybe five years, I absolutely trust them now. Similar with all of the other quality management systems that we've used 100s of, but you do tend to get what you pay for, so I completely understand why folks using the cheapest BMS they can find, using series FETS as a means of interruption are cautious about relying on it for the subtle aspects of energy storage system control, but I feel their experience and opinion is biased due to their lack of knowledge of how dependable a quality system can be.

Just my experience based opinion.

Batrium is good but has one flaw.

If you have 10 batteries and 1 cell is out of whack then it shuts down all 10 batteries.

Unless you want to run 1 supervisor, K9 or other cell monitor and a Trip breaker for each battery.

That’s why most don’t use it.

 

[Sean Very North]

Batrium is good but has one flaw.

If you have 10 batteries and 1 cell is out of whack then it shuts down all 10 batteries.

Unless you want to run 1 supervisor, K9 or other cell monitor and a Trip breaker for each battery.

That’s why most don’t ....

But thats not how a BMS is designed to function, and it's not how a correctly configured Batrium works. If one cell is a "runner", a competent BMS would lower the rate of charge, and bleed from the "runner" - allowing the remainder to catch up whilst not heat stressing the bleed components, there's absolutely no need to be shutting anything down.

If the runaway cell is a poor capacity match to the remainder of the bank, and is constantly causing issues that need BMS intervention then it should be replaced.

Battery management systems aren't intended to facilitate the use of cells of very obviously different capacity, the popular demands here for active balance management systems able of shifting high amperage around simply helps illustrate how many folks are using banks constructed using poorly matched cells.

 

[Nobodybusiness]

But thats not how a BMS is designed to function, and it's not how a correctly configured Batrium works. If one cell is a "runner", a competent BMS would lower the rate of charge, and bleed from the "runner" - allowing the remainder to catch up whilst not heat stressing the bleed components, there's absolutely no need to be shutting anything down.

If the runaway cell is a poor capacity match to the remainder of the bank, and is constantly causing issues that need BMS intervention then it should be replaced.

Battery management systems aren't intended to facilitate the use of cells of very obviously different capacity, the popular demands here for active balance management systems able of shifting high amperage around simply helps illustrate how many folks are using banks constructed using poorly matched cells.

A correctly configured Batrium does just what I said.
If you have a runner it will shut down the entire bank.
There is only 1 connection to a Shunt trip from the supervisor.

I don’t know where you’re buying your cells but all of them even from the same batch and manufacture have variances.

The only way you can “lower” the charge rate is to be able to talk to the inverter or CC.

Batrium doesn’t talk to Every AIO or CC.

@sunshine_eggo care to weigh in here.