LiFePO4 Batteries and Generator Starters

bajajoaquin

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Sep 1, 2021
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I am narrowing down my planned solar/battery upgrade for my motor home to William’s 400 watt with alternator charging system. I would be adding a separate charger for shore power/generator power. When I’ve made up my mind I’ll post a thread about my specific choices.

I think the last structural question I have is around the LiFePO4 battery (100AH) and my 4kw Onan generator. The SOK battery I’m looking at is rated for 100a continuous and I’ve seen that they can do 200a for 30 seconds. Onan isn’t clear, but it looks like they draw 250a as a surge then 60-100 amps (depending on the model) for the remainder of the cranking cycle (15-30 seconds).

Does anyone have personal experience with this (or similar) setup? Any other opinions?
 

bajajoaquin

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Sep 1, 2021
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Ouch. That’s going to require some re-thinking. Thank you for checking.

This probably means I have to run a wire to the truck battery.

edited: ooooh! I read that wrong. I thought you had written amps. Great! I won’t take that as my definitive answer but it’s good news.
 
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richard cabesa

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Mar 16, 2021
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Stay tuned. I run it again after sundown. My batteries were full with three SCC’s in float.
I do not know if the panels could have been affecting those numbers
 

richard cabesa

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Mar 16, 2021
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BMV712 readings after sunset 7 watt load from propane detector and some LEDs

1219 watts
846 watts
610 watts
401 watts
167 watts
All of that over 5 seconds of cranking and the generator fired

it is an Oman 4000 Q series

p.s. I have found the best way to start the gen is NOT long 15-30 second cranking session.
Push the Prime button
Wait 10 seconds
Crank 3-5 seconds
Wait a few minutes
Crank again and it will fire in 5 seconds
 
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newbostonconst

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Sep 24, 2019
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I am in the process for building a 20 cell 55ah battery to start and run my 1991 351cid Mustang.....good info....
 

bajajoaquin

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Sep 1, 2021
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Thanks. I wonder if there are some peak loads that are higher and shorter in duration than might be captured with the refresh rate. I’ll call Cummins and see what I can get. I have fairly low hopes, as others online have asked this question and not gotten a good response.
 

richard cabesa

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Mar 16, 2021
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I just hit the button again for grins

370 watts of solar coming in before I hit the button,
842 watts load after the push
1212 watts

Please let us know if you get something out of Cummins

i just can’t help but think that right around 100Amp is about right. The dang things are really just an 175cc motorcycle engine. Most of those have very tiny batteries with 100~120 CCA capacity
 

bajajoaquin

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Sep 1, 2021
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I was waiting to get the camper back from the shop before contacting Cummins, but it’s going to be a while. So I reached out just with the year and model number. I got a reply that they would contact me within 24 hours.

But I’m inclined to agree with you, Richard. They can’t draw that much juice.
 

bajajoaquin

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Sep 1, 2021
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According to Christian at Cummins, they draw a max of 80 amps.

Woo hoo! LiFeSO4, here I come!
 
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