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tonyjobson avatar image

Alternator Charge Current Estimate at 13.8 Volts

Hi,

I am planning the upgrades to lithium for my motor home. And I'm trying to estimame and budget for whether I NEED a battery to battery charger or if I can get away with just alternator charing through the BMS.

Looking to start with:

1 x Victron Lithium 12V - 100Ah Smart and CL BMS 12/100

I know i can limit the current using fuses on this BMS to protect my alternator.

Reading the litrature for the battery it recomends charge voltage of 14V to 15V. 14.2 being needed for cell ballance.

I'm only getting 13.8 volts from my alternator and I'm worried I wont be able to charge (or top up ) by lithium batterys without adding a B2B which can boost the voltage.

My question to anyone who can help me is:
My alternator only puts out 13.8 volts.

Will I still be able to charge the lithium pack at a sensible rate with a marginal voltage difference and below the recomended charge 14.0 charge suggetion?


I'd like to be able to top off the batteries at 50Amps from the alternator - is this feasable without boosting the voltage using a b2b?


Not knowing the internal resistance of the lithium pack I can't calculate the sort of charge current I could expect.

Does anyone have some first hand guidance of charging from alternators of lower voltage ?



thanks for the help

regards

Tony.


charging batteryLithium battery Smartalternator
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1 Answer
kevp avatar image
kevp answered ·

Tony, there are a couple of things to consider. First, is the alternator capable of providing the output for long periods of time? They can get very hot if charging continually at high loads, especially if you are cruising it top gear at low engine RPM. Take a look at this https://www.youtube.com/watch?v=jgoIocPgOug

Secondly, a lot of newer Euro 6 engines have alternators that ease back once the vehicle battery has topped up. This means there is not enough voltage to charge the camper battery.

I have a LiFePO battery in my Euro6 camper and after a few minutes my camper battery charge current drops off. Fortunately, the solar still charges when I drive too.

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