Onan 4kw, how much battery is required after starting?

[RVers29325]

I installed some house Li batts and a Li converter separate from generator starting battery. Generator has no converter/charger connected.

Cranked the generator to run a/c this summer for 48hrs straight.

Shutdown generator and tried to crank it again, battery was DEAD. Cranked chassis to charge generator battery, then started the generator.

(The thought was to charge the gen battery by the alternator while in transit and that would be good enough, thought wrong.)

Could I use a 2 Amp charger to keep the generator battery charged (plugged into an outlet in the camper while the gen is running) or do I need a bigger charger?

Thanks,
Phil.

[d23haynes57]

Originally Posted by RVers29325

I installed some house Li batts and a Li converter separate from generator starting battery. Generator has no converter/charger connected.

Cranked the generator to run a/c this summer for 48hrs straight.

Shutdown generator and tried to crank it again, battery was DEAD. Cranked chassis to charge generator battery, then started the generator.

(The thought was to charge the gen battery by the alternator while in transit and that would be good enough, thought wrong.)

Could I use a 2 Amp charger to keep the generator battery charged (plugged into an outlet in the camper while the gen is running) or do I need a bigger charger?

Thanks,
Phil.

Your RV should have been equipped with a converter charger or some means to charge the house battery when running the generator or plugged into shore/park power. Usually these are at least 30 amps in even the cheapest of units. Find it, see if it is working and if not why. You may also have combustion inverter/charger. Again, that should charge the house batteries while the genny is running. You may have some other 12 volt loads that a small charger cannot keep up with. Ideally you should add some battery monitoring so you can see what is happening.

Sorry! I missed the part that you did a non-standard battery install. You will want a charger to match the size of the batteries and also consider any connected 12 volt loads such as lighting, refrigerator etc. Typical charger should be sized to charge batteries in 4 to 8 hours. 200 A/H battery- 25 to 50 Amp charger. The generator does need 12 volt power to run even after it is started.

[RVers29325]

The original converter failed and thought it would be good time to install Li batteries and a Li converter. I disconnected the generator battery from the DC system and installed the Li batteries in the closet. Now I need to add a battery charger for the generator battery. Two different systems now.

I was wondering what size battery charger I would need to keep up with excitation current being drawn by the generator?

Thanks, Phil

[followingsea]

Originally Posted by RVers29325

The original converter failed and thought it would be good time to install Li batteries and a Li converter. I disconnected the generator battery from the DC system and installed the Li batteries in the closet. Now I need to add a battery charger for the generator battery. Two different systems now.

I was wondering what size battery charger I would need to keep up with excitation current being drawn by the generator?

Thanks, Phil

A much better description of the issue than in the first post. If nothing else this a cautionary tale of making a design change.

What is the voltage of the Li battery. I would think you could charge a 12 vdc battery directly.

I would also be concerned about putting a battery in a closet.

[RVers29325]

Oops, disregard. The battery is disconnected after startup! Now, I'm wondering why my battery died after startup. Hmmm? (This will be a different thread if needed.

Thanks, Phil

[RVers29325]

Thought this would be beneficial for reference.

[THenne1713]

The starter, solenoid, fuel pump, circuit board and (ignition on some) is 12vdc

[twinboat]

I would use a 10 amp automatic charger for the generator battery. Just because it says 10 amps, that doesn't mean it outputs that full time. An automatic charger tapers off the amp output depending on the batteries state of charge.

[Mudfrog]

Originally Posted by THenne1713

The starter, solenoid, fuel pump, circuit board and (ignition on some) is 12vdc

True but the Onan description posted by RVers states there are dedicated windings inside the genset that are supposed to power internal electronics and take care of battery charging after the genset is running.

Or maybe I'm just reading it wrong since KY models are normally used in RVs that have their own onboard charging systems.

RVers might try using a 12 volt capable amp meter to find where the draw is.

[SJ-Chris]

You mentioned your generator ran for ~48hrs and then died, and you are using a lead acid battery for starting/running your generator. Assuming your Lead generator start battery is ~100AH then (perhaps) your battery draw while the generator is running is ~2amps. (Note: We don't know what your lead acid battery starting state of charge was, so this number could be off...but if your lead battery was less than fully charged then it means your lead acid battery draw while the generator is running is actually less than 2amps.)


Between my house batteries and my chassis battery I have a Trik-L-Start device. Anytime something is charging the house batteries (ie. my solar, generator running, or plugged in at a campsite) this device will also allow the chassis battery to receive some charge. You could use a similar device between your Lithium charging system and your lead acid generator battery. Then, everything will be taken care of, it's a very clean solution, it doesn't require you to even think about it anymore.


Note: Trik-L-Start company went out of business. But there are alternatives. You can google: Trik-L-Start alternative and you will see many choices. Install it and your problem is likely forever solved.


Good luck!
Chris

[RVers29325]

Originally Posted by Mudfrog

... and take care of battery charging after the genset is running.

I don't think it takes care of charging the battery.

Originally Posted by SJ-Chris

You mentioned your generator ran for ~48hrs and then died,

Chris

After I ran the battery for 48hrs, I stopped the generator. Then tried to restart it a few hours later. That is when I found the battery was dead.

I have a deep cycle for the generator.

[Mudfrog]

Originally Posted by RVers29325

I don't think it takes care of charging the battery.

I'm pretty sure you are right, especially since the battery was dead after the 48 hour run. But you did post an image of a small fact sheet from Onan that states "Winding B1-B2 is for battery charging and internal low voltage loads". I'm curious as to what that means?

[dvspl]

Originally Posted by Mudfrog

I'm pretty sure you are right, especially since the battery was dead after the 48 hour run. But you did post an image of a small fact sheet from Onan that states "Winding B1-B2 is for battery charging and internal low voltage loads". I'm curious as to what that means?

I'm not sure what that means. I think the generator is self sustaining after starting, so it doesn't draw any 12 V power from the battery but also doesn't charge it. Here's what my Onan QG4000 Installation Manual says:

[Paul_D]

Why not use the LI batteries to start the generator. I have a single 100Ah LiFeP04 battery and it starts a Onan QG3600 LP.

The BMS is rated 100 A continuous and 280 A for 5 seconds.

More than enough kick to turn over the generator.

I'm still chasing down why the power shunt is showing a max draw of 279 A.

I know the generator is not drawing that much, and there is no battery combiner in the RV.