Small Engine Alternator to Lithium

[DC Indy]

My question is….. how big of a AGM would I need between the Small Engine Alternator Battery machine I built many years ago to handle using a DC-DC charger so I can charge my LIFEPO4’s without worrying about damaging them?

Alternator is a GM 10SL puts out 63amps….

I run the Honda Clone at 3600 rpm’s to get max alt output connected to a battery that I used to jump cars or attach an inverter in an emergency.

Well now I have backup system made with LiFePo4’s connected. I wanna attached my small engine system via a DCDC to charge the backups now as well if I need too.

Hints?????

 

[Larry-Cleveland]

I would think that the DC/DC charger would not care too much how it gets the 12-17 volts as it will change the input voltage to what it needs up to the max amps it is designed for to charge your batteries.

 

[smr.ruby]

I'm not sure I follow what you mean by "an AGM" in that context. Do you mean another AGM battery between the two?

The biggest problem with charging an LFP battery directly from a car alternator isn't that you will damage the LFP battery it is that the incredibly low internal resistance (compared to lead acid) of LFP will overload your alternator. I've done it before and the alternator can get quite hot. A typical car alternator rated for XXAmps is capable of that output but doesn't actually limit itself to that current. It will burn up and die if presented with a low enough resistance that it drives more load than rated for. All that said if I'm misinterpreting what you mean by AGM my response may go in the waste bin

you can fix this alternator overload by using a DC-DC charge controller like this one: https://community.victronenergy.com/questions/231777/orion-tr-smart-1212-30-65-amp-output.html

 

[DC Indy]

Yeah just don’t wanna burn up the alternator by going direct to Lithium. With a one wire alternator you should always have a battery connected to it while running. Or at least that’s what I’ve always been told.

So with that in mind I’d have the Alternator wired to an AGM thus wired to the DCDC to my lithiums…..

So that was my concern without burning up anything. What would be the smallest AGM to go between to give the 12v signal it needs to power on so the DCDC charger works properly.

Currently had an old starter battery standard Deep Cycle Marine type. It’s now bad and I’m looking for a new one to use. I mean could I get away with a 10ah 12v in between or should I go with something bigger? Remember to not burn either the Alternator or the Lithiums up in the process.

 

[smr.ruby]

Okay I understand better now. If you are using the DC/DC converter that can regulate the power draw from your alternator I'd have to agree with @Larry-Cleveland . I don't think any lead acid battery is required on the alternator side of the Dc/DC charge controller. I think the "notion" that you shouldn't run your car without a battery is more to dampen voltage changes for the sake of the other electronics in the car not to protect the alternator. It won't hurt to run an AGM battery of any size but I wouldn't hesitate to run without one either, seems unnecessary. Maybe try without and watch to see if your particular DC/DC is loading the alternator consistently. If it has wide voltage swings then a battery might help.

 

[Larry-Cleveland]

Yes, you will need an AGM battery on the alternator side to power the alternator up as it does not have any fixed magnets in it like a generator would. The battery will also act as a large filter and clean up the power going to the CD/CD charger.

 

[smr.ruby]

Yes, you will need an AGM battery on the alternator side to power the alternator up as it does not have any fixed magnets in it like a generator would. The battery will also act as a large filter and clean up the power going to the CD/CD charger.

you right... I was thinking of the case where you pull the battery after already running.

 

[mikefitz]

how big of a AGM would I need between the Small Engine Alternator Battery machine

Any lead acid battery over about 10Ah would work, suggest a 40 amp DC to DC.

 

[DC Indy]

Good deal. Thanks guys. Greatly appreciate the help.