Jump starting from DIY LIFEPO4 battery pack.. NEED ADVICE!

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Contributor II

98
Europe
First Name
s
Last Name
K
Hi guys... need some advice!

Earlier this year i build myself a big Lithium 105AH battery pack:

So far the pack is working fine.

My question is:

Can i use the 125A ANDERSON connector to hook up some fairly beefy jumper cables with an ANDERSON connector
and jump start my or any car that way..?

1. We can do this by letting the battery's be connected to each other and let the low 40AH (acid) battery balance and hopefully have a high enough voltage to start..
disconnecting the DIY LIFEPO4 pack first before trying to start the car.

2. Or leave it connected to the DIY LIFEPO4 pack and jump start it like you normally do with a "normal" jumpstarter.

Problem i see with method 2. is i could blow the 125A fuse behind the ANDERSON plug, damage the 200A relay, the 200A main power switch
and or blow up the last 400A fuse between the Main switch and LIFEPO4 pack.

Here are some photos to show you how i have the ANDERSON plug connected:

BorealOverlandIMG_4714.JPG

BorealOverlandIMG_4716.JPG

BorealOverlandIMG_4720.JPG

The Victron Battery Protect in the photo is not in line with this ANDERSON plug,
it only powers the 200A Relais that powers the ANDERSON plug from busbar.

What i also can do is neglect the 125A ANDERSON plug and just put a normal set of jumper cables directly
on the beefy 3 way M8 busbars you see on the left (+) en right (-) of the pack.
If i do that there is "only" the 200A Main switch and the 400A fuse in line..

So what would be the best way to go about this..?

Hope you guy's can give me some advise on this matter.

Thanks for your help, stay safe!

Steve
 

Contributor II

98
Europe
First Name
s
Last Name
K
From what I have read, and it may have been wrong, the lithium battery will suck every amp out of the starter battery, not charge it.
Hi Larrie,

Thanks for your response!
Yes i know Lifepo4 can suck up a lot of amps..

Might just test it on another battery i have laying around, just as an experiment.

Thanks again.

Steve
 

slomatt

Rank V

Influencer I

1,723
Bay Area, CA
What kind of car are you hoping to jump start? I did a quick search and it seems that many cars can require ~400A to turn over the engine.

Jumping off the LiFePo4
With your 105Ah batteries this would represent a drain of ~4C, can your batteries support that? 400A is also more than your Anderson plug, fuse, switch, and relay are rated for. You could go directly to the large bus bars but then would still be limited by the 200A switch, though it could potentially be ok since the draw would be for a short duration. A lot of commercial lipo jump packs claim 800A+ but have suspiciously small wires, which indicates they don't need to source high current for all that long.

Charging directly from the LiFePo4
Many car batteries are designed to charge at ~13.8 volts and given that your pack is 13.3 volts @ 90% charge you could potentially connect it directly to the car battery to charge it. I'd be careful about this though since I'm not sure how much current flow you'd have.

Isolated Charging
You could use a 12v DC-DC charger to isolate the batteries and use the LiFePO4 to charge the car battery. It would take a while, but should be safer than a direct connection.
 
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Contributor II

98
Europe
First Name
s
Last Name
K
What kind of car are you hoping to jump start? I did a quick search and it seems that many cars can require ~400A to turn over the engine.

Jumping off the LiFePo4
With your 105Ah batteries this would represent a drain of ~4C, can your batteries support that? 400A is also more than your Anderson plug, fuse, switch, and relay are rated for. You could go directly to the large bus bars but then would still be limited by the 200A switch, though it could potentially be ok since the draw would be for a short duration. A lot of commercial lipo jump packs claim 800A+ but have suspiciously small wires, which indicates they don't need to source high current for all that long.

Charging directly from the LiFePo4
Many car batteries are designed to charge at ~13.8 volts and given that your pack is 13.3 volts @ 90% charge you could potentially connect it directly to the car battery to charge it. I'd be careful about this though since I'm not sure how much current flow you'd have.

Isolated Charging
You could use a 12v DC-DC charger to isolate the batteries and use the LiFePO4 to charge the car battery. It would take a while, but should be safer than a direct connection.
Hi, thanks much for your response!

My car is a 2011 Mitsubishi Outlander, with a (small for USA standards) 2.0L petrol engine.. and has a 60AH battery.
so not a big diesel or something that i had in mind for backup jump starting.

The prismatic cells i used for my battery pack can handle a short 300A - 400A pulse i see in the specs..
so in a pinch i think i can get away with that. Like you said, the switch should be ok if i don't make a hobby out of it..
Only thing between the switch and battery is the 400A fuse.. that might blow but can be replaced if need be.
Yes, i also noticed the small wires on a lot of those jumper packs.

I have not thought about using a DC to DC charger from my battery pack to starter battery...
But i have been thinking about getting the latest Victron Smart DC DC charger for charging my battery pack when i am driving the car on longer trips.
This should also work the other way around (but without power from the altenator of course).
Maybe that's the best and safe way of doing it like that,
and simply hook up the DC to DC with Anderson plugs so that i can make it work the other way too.

Thanks very much for your input!
Gives me something to consider..

BTW, i could just buy a small jump pack as a backup of course,
but just looking and thinking about what options i have with the goodies i already own.

Steve.
 

slomatt

Rank V

Influencer I

1,723
Bay Area, CA
Steve,

I like the idea of using a single DC to DC charger to both charge the pack from the car or to charge the car from the pack. And given that your cells can handle a 400A pulse I would guess that you can jump straight off the pack if you needed to. I've jumped cars off a small 28Ah AGM battery many times.

Nice job on the layout and build of your battery pack by the way. I recently built a 24v ~300Ah system for my house (discount Powerwall) but it's not as organized. :)
 
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Contributor II

98
Europe
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s
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K
Hi, thanks..

It took me some time to figure out how to get it all connected and working the safe and proper way,
gathering all the right components and cramping it all inside this fairly small box.
It was a big puzzle, but a fun one and i learned a lot from it!!

That's awesome man, that a powerful pack!

I would like to build a "powerwall" from LIFEPO4 cells myself in the near future..
This year i bought a 48V HYBRID Solar inverter for the 4000W of panels i have laying on my roof.
It can handle 4000W Solar and invert 5000W at 230Volts.. (when battery's are hooked up).
I also have a "normal" grid tie inverter but i like the idea of the 4-way HYBRID in say a "grid down" situation.
That way (if i finally hook up a 48V battery pack) i still have power to my fridge and heater.
Plus the grid tie stops at 3000W but the Hybrid nicely soaks up 3600-3700W at peak moments.
Getting off topic here lol..

Steve.
 
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slomatt

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Bay Area, CA
My "discount powerwall" is based around a used 8S LiFePo4 battery that was originally rated at ~5kW, which I figure is probably down to 3.5-4kW of capacity at this point. The battery is managed by a 8S BMS that does passive balancing, and the system is controlled by a 24v Growatt unit which contains a 3kW pure sine wave inverter, 2kW solar converter, battery charger, and a transfer switch.

California has experienced multiple "public safety power shutoffs" over the last few years so I built this "powerwall" to power our refrigerator and tankless water heater when the grid is down. At some point I plan to hook it into the electrical panel, but for now I just have an extension cord in place so I can plug the fridge into the inverter. It works well, the one problem I've had is that the cells in the battery are not well balanced so I can't use it's full capacity. When I have time I plan to bottom balance the cells to try to get them more even.
 

phxdsrtrat

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I agree with the use of a DC to DC charger for both charging the pack from the vehicle or vice versa. This is a good approach. I suspect jump starting from an LiFePO4 pack even a few times may shorten the life of the cells so its not an approach I would take. I actually pack a dedicated jump start pack (they aren't expensive compared to an LiFePO4 setup) if a really need to "get going now". Otherwise my 1000 watt hour (not do it yourself) has a circuit to charge a vehicle via a built in DC to DC charger.

-Curtiss