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ianmcnobody avatar image
ianmcnobody asked

How to engine charge Pylontechs?

I am trying to figure out how to safely and efficiently charge my 48V Pylontech 4.8kWh US5000 LiFePO Battery setup using my narrowboat engine...

I have been advised by a trusted boat electrician that drop-in batteries like pylontechs can’t be charged directly from alternators, not even using regulator-controlled high-spec alternators, as the stop charge signal from the Pylontech BMS causes too much of a voltage spike that would damage the alternator and the regulator…

Can anyone advise on how I might be able to resolve this without losing too much of the efficiency of charge that lithiums offer?

I have heard people mention hybrid batteries (using a Lead Acid battery to absorb or protect from the voltage spikes somehow?), or using a DC to DC charger from the 12V starter batteries (I would assume this would negate the efficiency of charge that you can get with Lithiums, but maybe there's a setup that works around this)?

battery chargingLithium BatteryPylontechalternator48v battery
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kevgermany avatar image kevgermany ♦♦ commented ·

Tricky one. The US5000 needs a lot of current at 48V.

A little more information needed please.

One alternator, shared with starter battery, or a second for the house battery?

What voltage alternator(s)?

Do you have any other Victron kit like a multiplus, or Cerbo?

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
As far as I know Pylontech batteries are not designed to be used in vehicles (RV or boat) only for stationary systems like ESS.
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ianmcnobody avatar image ianmcnobody Matthias Lange - DE ♦ commented ·

I didn't realise you'd both replied - apologies!


I have 2 alternators - 1 x 65A and 1 x 175A (standard spec on a Beta 90T Greenline engine) - both 12v.

My pylontech batteries are connected via a Lynx Distributor to a EasySolar II GX 48/5000/70, with the built-in mppt connected to a 1600W PV array.

I am now planning to connect the 175A alternator to a 130Ah AGM battery that will connect to a Sterling 12v to 48v 70A charger - https://www.bimblesolar.com/sterling-pro-ultra48-12 - which will be wired into the Lynx Distibutor (with 80A fuse and 32A switch), and I'm hoping that this isn't a hopelessly inefficient way to charge the Pylontechs?


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Alexandra avatar image Alexandra ♦ ianmcnobody commented ·

https://www.seatronic.fr/en/dc-dc-charger/1798-battery-to-battery-charger-12v-48v-17a.html



Possibly might be easier to switch the alternator up to 48v one? Dont know never looked at that.

https://community.victronenergy.com/questions/41792/how-to-charge-a-48v-system-from-a-12v-vehicle-alte.html

https://diysolarforum.com/threads/can-you-charge-a-48v-system-with-a-12v-alternator-other-questions.6480/

Victron does a 48/12 (so the other way) converter but it is not a charger

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Justin Cook avatar image Justin Cook ♦♦ ianmcnobody commented ·
Be aware that the Sterling BB1248-70 is 70A draw from the 12v side, not 70A delivery to the 48v side. Counting device inefficiency and other factors, you'd be looking at maybe 12-13A of charge current to the 48v bank from that Sterling.
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kevgermany avatar image kevgermany ♦♦ Justin Cook ♦♦ commented ·
I guess two can be connected in parallel, which would pull 140A from the alternator. On the high side, especially as narrowboat engines rarely run much over tickover speeds.
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pwfarnell avatar image pwfarnell ianmcnobody commented ·
When the smaller Beta engines are used for hybrid propulsion with a 48V battery bank, the 12V 175A alternator is replaced with two 24V 60A alternators in series to give 60A at 48V, a nominal 3kW charge power. Another approach would be to add a Travel Power 240V ac alternator, either 3kW or 5kW and feed this in to the EasySolar to do the charging. All these options are of course probably more expensive than a battery to battery charger.
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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

If you run the engine at or near idle, you will need to adjust the pulley on the alternator to make sure it has good operating rpm, also make sure the engine can provide the power to drive the alternator too. Running the alternator to an AGM battery is a good idea, though I would have started with a 24V alternator and system. To charge the pylontech's you need to keep the charge current within the 0.5C rating - for max charge, and preferably be able to reduce the charge current on demand by the BMS - as cell voltages approach max, and balancing occurs.

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