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David Heckley avatar image
David Heckley asked

Best way to jumpstart a Sprinter with Victron LiFePO4 batteries and a smart alternator

Hey there, I am trying to figure out the best way to add a feature to a sprinter van where I can jumpstart my starting battery off of my lithium coach battery set. I was thinking of some sort of momentary switch on the dash that could be held to act as the jump start in the event of starter battery depletion - but only that.

I have been trying to work in a cyrix-lt-cr but it seems like it has a 30 second hold, and only engages at certain voltage levels?


The big concern I have is with the smart alternators and ensuring the ability to isolate the lithium batteries from it so I don't overcharge the lithium or burn out the diodes in the alternator. I currenty use a DC/DC buckboost charger to modulate the charging current to a safe level, but short of installing a second buckboost I'm not sure how best to configure a jump start feature safely

wiringstarter battery
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2 Answers
ripper avatar image
ripper answered ·

I would not start off the Lifepo directly. The starter might need more than the rated current especially in winter. If the BMS shuts off due to over current regularly you may have more expensive problems and the engine is still not running with a full battery. Size whatever drains starter battery (lights, heater or whatever) and get smallest Orion galvanic isolated unit (6 terminals not 4) This can be turned off when regularly parked and can be adjusted to set voltage ie 13.8V when camping commences and keeps it topped off till Lifepo is empty. No need for the expensive 3 stage model since starter battery never gets discharged. Starter battery is fully charged and items will be powered without cycling starter battery.

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David Heckley avatar image David Heckley commented ·

Got it, that makes a lot more sense. Jump starting would be an over 1C discharge rate, so either applying a float charge or 1C charge rate for a longer duration would assist in a dead battery state.

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llubi avatar image
llubi answered ·

I'm doing it with a 250A VW relay, no problem at all.
For charging I upgraded to a Orion B2B when I switched to lithium, but I've another 70mm2 cable from the rear battery to the engine, with a relay supplied by VW. If I want, I can jumpstart from my leisure batteries.
Did test with the 100A and 200A-a Victron batteries, no problem at all. Now I'm using 200A chinese aluminium cells, and it's the same. Starter makes the same noise and need the same amount of time as with the AGM from the engine bay.
Next step, in some weeks, change my engine AGM for 60Ah Winston cells, let's see if it works, and how long!

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