charging start batteries

[trvsndrsn]

I have a toy hauler that i have converted to lithium batteries. I have 4 100 ah lithium batteries. 400 watts of solar. 90 amp lithium charger. 1000 watt inverter. 5500 watt onan generator with 2 lead acid batteries.

I want to be able to charge the lead acid batteries that are for starting the generator from the lithium battery bank. The generator has no output to charge its own start battery. I looked at a few dc to dc chargers and they all seem to have an ingnition wire that doesn't work for my application. Could I use a solar mppt charger as a dc to dc converter. Just connect the input to lithium bank instead of solar panels?

My generator has an auto start that will start at a voltage I set. The rv has a 90 amp lithium charger that will begin to charge the lithium bank. also have a mppt 400 watts solar charger connected to the lithium bank. could I add a second mppt solar charger to charge the lead acid batteries.

 

[timselectric]

SCC requires a minimum of 5 volts input over charging output voltage. Possibly more.

 

[Minimoose]

I have a toy hauler that i have converted to lithium batteries. I have 4 100 ah lithium batteries. 400 watts of solar. 90 amp lithium charger. 1000 watt inverter. 5500 watt onan generator with 2 lead acid batteries.

I want to be able to charge the lead acid batteries that are for starting the generator from the lithium battery bank. The generator has no output to charge its own start battery. I looked at a few dc to dc chargers and they all seem to have an ingnition wire that doesn't work for my application. Could I use a solar mppt charger as a dc to dc converter. Just connect the input to lithium bank instead of solar panels?

My generator has an auto start that will start at a voltage I set. The rv has a 90 amp lithium charger that will begin to charge the lithium bank. also have a mppt 400 watts solar charger connected to the lithium bank. could I add a second mppt solar charger to charge the lead acid batteries.

Why not just charge the lead acid with a standard charger from the inverter? My 15 amp Schumachers only pull about 150 watts each. Just a thought.

 

[trvsndrsn]

Why not just charge the lead acid with a standard charger from the inverter? My 15 amp Schumachers only pull about 150 watts each. Just a thought.

I have thought of that. seems like a terrible inefficient way. convert 12 volts to 120 then back to 12 volts. also was hoping to have some bluetooth information.

 

[trvsndrsn]

SCC requires a minimum of 5 volts input over charging output voltage. Possibly more.

would a dc to dc charger require the same?

 

[Minimoose]

I have thought of that. seems like a terrible inefficient way. convert 12 volts to 120 then back to 12 volts. also was hoping to have some bluetooth information

I guess it depends on how you look at it. If I can use the power of the sun without losing battery capacity I consider that efficient. If your panels are capable of keeping your lithium batteries at a full charge while charging the lead acid batteries I consider that efficient.

 

[12VoltInstalls]

The generator has no output to charge its own start battery

That doesn’t sound right. It should charge while running…

could I add a second mppt solar charger to charge the lead acid batteries.

Not off the same panels.
But a simple separate 100W panel and basic pwm would do
It. (Or the littlest Epever mppt)

 

[HRTKD]

That doesn’t sound right. It should charge while running…

He's right. The generator does not charge its starting battery. I have the same Onan 5500 watt generator and verified this with an ammeter. Once started, it's not a huge draw, but if you leave the generator running long enough it will bring the battery down.

@trvsndrsn, my solution is this:
1. The 7-pin connection charges the lead acid battery. The LiFePO4 battery bank does not get any charge from the 7-pin.
2. I have a 170 watt solar panel that keeps the lead acid battery topped up.
3. There is a AC-DC converter that charges only the lead acid battery. This is on only when there is shore power or the generator is running. It does not connect to the LiFePO4 side.
3a. I'll be removing the converter soon. My Victron Multiplus has a trickle charger output. I'll be connecting that to the wires that the converter is currently using. That will cover the draw from the running generator.

 

[12VoltInstalls]

He's right. The generator does not charge its starting battery

That does not compute!

Of course I’ve only dealt with backup generators and portables with a pull-start but I’ve never seen a ‘dumb’ generator I don’t think.

 

[HRTKD]

That does not compute!

Of course I’ve only dealt with backup generators and portables with a pull-start but I’ve never seen a ‘dumb’ generator I don’t think.

The way I think of the Onan 5500 is that its whole purpose in life is to generate AC. It doesn't generate DC.

 

[12VoltInstalls]

The way I think of the Onan 5500 is that its whole purpose in life is to generate AC. It doesn't generate DC.

Does it have a circuit from the vehicle charging system?

And I can’t believe they wouldn’t just throw magnets in something rotating and at least magneto recharge?

You have officially blown my mind.

 

[HRTKD]

Does it have a circuit from the vehicle charging system?

And I can’t believe they wouldn’t just throw magnets in something rotating and at least magneto recharge?

You have officially blown my mind.

In my case, the RV "house" system is isolated from the starter battery that is used by the generator. It's a trailer, not a motorhome.

The easiest explanation I saw was that the windings don't support DC generator. I can't explain it any more than that. If DC can be used to start it, why can't it generate DC? From what I understand, there is no separate starter on my generator, which furthers my confusion.

 

[Browneye]

Onan generators don't have a 12V alternator or generator.
The perfect solution for charging start batteries is:
1. Their own PV and SCC - that's what I did. 100W panel and a 10A controller. Perfect.
2. Install an 'amp-l-start' or 'trik-l-start'. Had I known about these at the time I would have went this way.

AMP-L-START Starting Battery Charger/Maintainer - Overview Page

15 Amp Starting Battery Charger/Maintainer

www.lslproducts.net

 

[12VoltInstalls]

easiest explanation I saw was that the windings don't support DC generator.

A car alternator works the same way- makes AC but is rectified to DC, just in 12V range not 120

I can't explain it any more than that. If DC can be used to start it, why can't it generate DC? From what I understand, there is no separate starter on my generator, which furthers my confusion.

Know nothing of this. It may use a capacitor dump? I would think it had a starter motor of some form.

DC charging is a different story - yet ~50 year old boat motors used generators or magnetos to charge batteries- or had no charging ability.

My 40-horse Suzuki had magneto ignition so on that I didn’t care; a foot of rope with a dead battery would start instantly. Once running it made 6-8A charging.

I can’t fathom a generator with no charging for the starting battery. It can and is done!

 

[trvsndrsn]

Onan generators don't have a 12V alternator or generator.
The perfect solution for charging start batteries is:
1. Their own PV and SCC - that's what I did. 100W panel and a 10A controller. Perfect.
2. Install an 'amp-l-start' or 'trik-l-start'. Had I known about these at the time I would have went this way.

AMP-L-START Starting Battery Charger/Maintainer - Overview Page

15 Amp Starting Battery Charger/Maintainer

www.lslproducts.net

That amp l start is the best solution I have seen so far. If I pair it with a Bluetooth monitor might be the ticket

 

[Peterbylt]

On my Bus conversion I needed a way to maintain the Bus Start batteries when sitting for up to 4 or 5 months.

I have six 250 watt panels, I have installed a switch so when the bus is sitting not being used I switch two of the panels over to an MPPT charge controller that is dedicated to just keeping the Lead Acid start batteries charged.
https://www.amazon.com/HQST-Controller-Negative-Bluetooth-Regulator/dp/B0989NV7M1?th=1

When we are using the Bus I switch the panels back to the charge controller that charges the LifePo4 House batteries.



Funny story, On the first trip after I configured the panels like this, I left the panels connected to the Start batteries, the dash light for a bad alternator kept coming on then going off, eventually I realized when I got in full sunlight the solar power was messing with the Voltage regulator on the bus and causing the Dash light to go on, when We went under a cloud or into the shade the dash light went off, lesson learned, flip the panels back to the house batteries before driving.

Peter

 

[timselectric]

would a dc to dc charger require the same?

No, it's more of a monitored switch.

 

[pollenface]

I think a good option would be a ~5a maintenance charger direct from your generators AC output. It will offer redundancy by replenishing the battery immediately after starting when no solar is available.

 

[Browneye]

In my case, the RV "house" system is isolated from the starter battery that is used by the generator. It's a trailer, not a motorhome.

The easiest explanation I saw was that the windings don't support DC generator. I can't explain it any more than that. If DC can be used to start it, why can't it generate DC? From what I understand, there is no separate starter on my generator, which furthers my confusion.

Your onan surely DOES have a starter. [shrug] And it draws pretty good when starting - something in the 150-250A range.

Winnebago connects the generator to the house system which makes no sense to me - if your run your batteries out you can't start your generator either. I gather the proper procedure is to start the engine, which would combine the two systems with the isolator solenoid, or use the combiner/boost button on the dash to do the same thing.

I move the main 12V lead to the generator over to the starting circuit with my lifepo4 upgrade and solenoid removal. Problem solved.

Also, for a motorhome, once the generator is started then there's 120AC, and they all have a 12V converter/charger that would then charge the house batteries. And therein is the designer's logic is my best guess.

Even more funny was the 10W solar panel they had offered as an option for this 2005 model - connected to the house batteries. Really?? I found the lead and thought I would be smart and connect it to the starting batteries instead. Which was all fine and good except with no solar controller it eventually cooks the starting battery. After replacing it the second time I got a little Battery-Tender controller and that took care of that. I have since replaced that 10W with a 100W and a 10A SCC, and added a second starting battery in parallel. We ain't never gonna have a dead starter.
The hardest thing to wrap my head around is not needing or having a 12V converter/charger in the first place. Sure, all house loads go directly off the battery, but if you have solar charging then it's all kind of moot.

 

[time2roll]

I looked at a few dc to dc chargers and they all seem to have an ingnition wire that doesn't work for my application.

Consider a small voltage controlled relay board to activate the DC-DC signal wire. Fully adjustable.

https://www.ebay.com/itm/383760514786

Forget the wire diagram. Battery connects to battery terminals as shown. Relay controls the signal wire.

The Amp-L-Start looks like it connects at 13.0 volts and disconnects at 12.8 volts. A bit low to protect LFP as it was designed on FLA batteries.