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jurjenhoekstra asked

Alternative method for charging LifePO4 battery with alternator

alternator-inverter-lifepo4.jpgOn my motor yacht I want to replace the house bank battery 720 Ah lead acid with a 400 Ah LifePO4 battery. Currently I use a Sterling Power Split Pro R which after the starter battery has been charged by the 150 A alternator, charges the house bank. I also use a Sterling Power external regulator to optimise the output of the alternator. This works well. If I replace the lead acid by LifePO4, the external regulator is not suitable to charge the LifePO4 battery, due to the low resistance of the LifePO4, which will cause the alternator to continuously deliver maximum charge and will most likely burn out the alternator and possibly damage the LifePO4.

After having researched this situation now for a couple of months I know that the solution is to remove the Split PRO R and put a DC-DC charger between alternator and the two batteries. But most 24 V DC-DC charger can not deliver more then 50 A. Which makes my 150 A Alternator inefficient and charging a bit slow. You can add a second DC-DC charger in parallel to double capacity. The Quattro can serve as a LIfePO4 charger with it's special LifePO4 charging profile, but only when connected to shore. Out on the water the Quattro does not charge, unless I start a generator, which I do not have.

I thought of a different solution, to most efficiently use the Quattro while on the water. If I add a Victron Inverter 24/3000 Smart after the Pro Split R and feed the 230 V output to the generator input (AC in 1) of the Quattro, it should be able to charge the LifePO4 with approximately 125 A.

Will this work? Does anybody have this solution? Am I overlooking something? Ideas/suggestions?

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2 Answers
chrigu avatar image
chrigu answered ·

Your solution is an inverter cascade. Altough it has been done succesfully, and i guess also stable, its not officially supported.


Two 50A orions get you to 100A charging. Are you sure that those extra 25A of charging capability trough the quattro are worth it?

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jurjenhoekstra avatar image jurjenhoekstra commented ·
Thanks for your input. There are no 24 V 50 A Orions.
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pwfarnell answered ·

Why not fit something like a Wakespeed WS500 alternator regulator to your alternator as this handles lithium charging. You may need to remove the alternator regulator as the Sterling regulator is often used as just an add on.

The decision also needs to factor in what type of batteries you have. If you have Victron Smart batteries with a Lynx BMS then that will shut down the alternator before a BMS disconnect occurs. If you have drop in ba and a BMS disconnect occurs the alternator will spike the voltage so you may need to consider an alternator protection module.

Re your suggestion of adding a Multiplus to generate ac power to feed the Quattro. You would have to make sure your ac wiring was set up so that you either feed grid into your knew Multiplus so grid and both inverters synchronise or make sure that you can never have the Multiplus output connected when there is grid power because the Multiplus would not synchronise with the shore power. Secondly, I am not keen on this from a conversion efficiency point of view. The dc to ac and ac to dc conversions will be say 90% efficiency at best, so to get 125A into the batteries you will need the alternator to produce 125 ÷ 0.9 ÷ 0.9 = 154A minimum which equals dead alternator from overheating. Additionally, a typical alternator will only produce long term 50+70% of its rating unless it is a special heavy duty one with a hot rating of 150A..

Some more thinking required, best options DC to DC charger(s) or a Wakespeed.

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jurjenhoekstra avatar image jurjenhoekstra commented ·
Thanks for you extensive input. There is only 1 alternator. I want to charge with the 150 A alternator both start battery and house bank. Wakespeed would work if I had 2 separate alternators. The alternator has produced in the past 175 A. I suggest adding a 24/3000 Smart inverter, not a Multiplus. A dedicated switch might have to be added to prevent shore power and inverter to charge at the same time, although engine off is inverter off.
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mattyroo avatar image mattyroo jurjenhoekstra commented ·
Fit a Zeus or Wakespeed regulator to the alternator, that will charge the house bank. The Zeus is superior to the WS500 in my opinion, as it offers "Generator Mode", meaning you can properly load the engine should you want to charge from the engine whilst at anchor. Between the house bank and the start bank fit a small DC/DC charger, which will keep the start bank topped up. You don't need a large DC/DC charger to the start bank, as they're charged in only a few minutes post engine starting.
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