Lifepo4 charging from alternatot

[Bikerwookie]

I have 200ah of lifepo4 that charges through a Renogy dcc50s at around 45A from a 55A hitachi alternator on a 3ym20.

I upgraded the alternator to the hitachi lr180 80A model.

Problem is it now puts out more amps then the 50A Renogy dcc50s can handle so it cuts in and out.

My next thought is to go back to the cristec charge splitter and charge the lifepo4 from the alternator. It’s 14.4v with the loses by the time it’s at the lifepo4 bms.
The alternator has temp compensation and I don’t need more than 80A charge.

Is this a bad idea?

 

[Poey50]

I have 200ah of lifepo4 that charges through a Renogy dcc50s at around 45A from a 55A hitachi alternator on a 3ym20.

I upgraded the alternator to the hitachi lr180 80A model.

Problem is it now puts out more amps then the 50A Renogy dcc50s can handle so it cuts in and out.

My next thought is to go back to the cristec charge splitter and charge the lifepo4 from the alternator. It’s 14.4v with the loses by the time it’s at the lifepo4 bms.
The alternator has temp compensation and I don’t need more than 80A charge.

Is this a bad idea?

I'm assuming that in your present set-up the alternator charges your start battery and the Renology charges the LFP from the start battery. Rod Collins of Marine How To recommends that the alternator should be double the capacity of the DC-DC charger so you are a bit under-specced.

The problem with using the splitter is that you will have no means of regulating the current to the LFP. That's no problem with lead acid since the increasing resistance with charge makes it self-limiting. The LFP will keep taking charge until the BMS disconnects - not a good plan. I think the best bet would be an external regulator (e.g. Balmar 614) which you can set up for LFP charge parameters. You could then charge the LFP directly and use the Renology to charge the start battery from the LFP (although it is probably a bit sophisticated for that). A Sterling Alternator Protect would be a good idea too, if you are going to use direct charging, in case of a BMS high voltage disconnect.

 

[Bikerwookie]

Thanks

Yes stage Renogy charges the lifepo4 from the engine battery. The engine battery is just a Agm.
The Renogy seems to want less amps than rod collins suggests. I only had the issue after the 80amp alternator upgrade. I thought it might fool the alternator in to thinking it should only supply 50a but I was incorrect.

To my mind ( and I maybe wrong) the alternator regulates the current to the lifepo4. The 80a hitachi lowers its output based on temp so it will try and put 80a in but will get hot and then drop the output down.

I like the look of balmar but not the price and alternator modifications I would have to do. I like to keep it simple too.

Fully agree that hitting the bms high voltage disconnect is one fail safe away from a very bad day.

So given the above can anyone foresee issues.

 

[Poey50]

To my mind ( and I maybe wrong) the alternator regulates the current to the lifepo4. The 80a hitachi lowers its output based on temp so it will try and put 80a in but will get hot and then drop the output down.

Yes your present set-up will work if you accept that the alternator switches on and off because of alternator temperature. If internal regulators were suitable for LFP no-one would ever buy an external regulator. Internal regulators work fine with lead acid because the lead acid progressively limits the charge that it can accept - not so for LFP.