Lithium batteries and starting the generator

So, I have been looking at upgrading to Lithium batteries and have everything figured out except for the requirements on starting the generator, which we would still use for the microwave. Folks stating specs say 450 cold cranking amps are required but anecdotally there are reports of no problems with just 2 100Ahr batteries (verses the 4+ the specs would indicate). I am trying to fit the batteries into the current battery compartment to make the change easier, so that limits the battery space.

My generator starts hard unless started daily so not wanting to risk damaging batteries.

My question is: If you are using lithium and the generator, what are your lithium battery system details: manufacturer, battery AHr, number of batteries. Any other related info you have gleaned on this issue would be appreciated.

Thanks!

..Mike

Two - 100 amp/hour Battleborn Lithium batteries.  We have had no issues staring our generator.   

Same here..2 battleborn batteries @ 100 amps and no problem starting generator

Cold cranking amps are not related to amp hours rating.

450 amps for 1 minute = 7.5 amp hours

Typically deep cycle and/or Lithium batteries are not rated in cold cranking amps

As a side note, I have always disconnected my house batteries over the winter but to exercise the generator, I simply started the engine, waited 20 seconds and then started the generator using only the engine battery (since the house batteries were physically disconnected).  I never had a problem doing that.

DKCruzser and Funseekers: Thanks for your replies!
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Cold cranking amps are not related to amp hours rating.

450 amps for 1 minute = 7.5 amp hours

 **true, but you still supposedly need the amps and 100ahr lithiums are typically rated as 100A max (often 200A surge for a "short" time)**

As a side note, I have always disconnected my house batteries over the winter but to exercise the generator, I simply started the engine, waited 20 seconds and then started the generator using only the engine battery (since the house batteries were physically disconnected).  I never had a problem doing that.

**Also true but I just don't want to start the RV every time I want to start the generator.**

Edit: It is interesting and useful info that you can start the generator with the house batteries totally disconnected. This would cover the harder starts during the winter monthly exercising the batteries. 

Use the maximum continuous discharge current spec, not Ah or CCA. For lithium ion batteries  that’s limited by the internal BMS.

From the Battle Born manual:

"Multiple BB10012 may be mounted in parallel in order to increase the current capacity of the system. When batteries are mounted in parallel, the voltage of the system does not change, but the current limits are additive. For example, two BB10012 batteries mounted in parallel can deliver 200A continuously and 400A for 30 seconds. Three BB10012 batteries mounted in parallel can deliver 300A continuously and 600A for 30 seconds. Therefore, all cables and connections MUST be able to accommodate the high currents that can be delivered by the battery. Appropriate fuses and circuit breakers are also highly recommended to protect downstream components from current spikes and short circuits."

Reply to GANDALF42

Edit: It is interesting and useful info that you can start the generator with the house batteries totally disconnected. This would cover the harder starts during the winter monthly exercising the batteries.

To start the generator using engine battery you must have the ignition on, you don't necessarily need to start the engine, but if you don't you are lowering voltage in that battery.

The two SOK 206ah batteries installed in my modified battery compartment on our 2018 2552 start the 4K generator even when down to under 20% SOC.

They also run my AC or microwave running through a Victron inverter.

The two SOK 206ah batteries installed in my modified battery compartment on our 2018 2552 start the 4K generator even when down to under 20% SOC.

They also run my AC or microwave running through a Victron inverter.

Thanks for your comment! Since the SOK's are not sealed, did you ensure the battery compartment was sealed or did you seal the batteries some way?

In modifying the battery compartment, did you just take out the drawer or ?

Thanks!

I assume you have separated the generator starting current requirements into the brief "inrush" demand, and the actual cranking current needed for longer duration.  The CCA requirement specified by Onan (450 amps or whatever) relates to inrush--which on the Onan 4000 has been measured at about 350 amps but exists for less than 500 milliseconds.  Actual cranking current depends on battery voltage, but should run about 70-75 amps for whatever duration until the generator starts.

These may be some of the reasons why, in actual experience, folks have no problems with their lithium setup handling the generator demand, even with lower state-of-charge.
Mike

Mike, No I didn't know this distinction and so, this info is very helpful. It clears up the specsmanship a lot. Thank you.

It is interesting that Battle Born Batteries in their FAQ imply their understanding of cold cranking amps drawn on their lithiums  is a measure of surge current over time:

"Can you batteries start my Onan generator?

Onan are one of the most popular generators on the market for RV applications. Most RVs and campers come equipped with a generator, and the Onan is compact enough to fit into most camper’s cargo spaces.

Onan Generators startup requirements typically run between 360 and 475 cold cranking amps. Although two of our batteries will almost always start your on-board generator, three of our batteries are an ideal match."

This comes from a company with one of the stronger discharge surge ratings: 200A for 30 sec.

That would equate to 400A for 2 batteries and 600A for 3 for 30 seconds, a conservative answer.

I am going to try and get a clarification on the spec and current requirements from Cummins.

Just looked at the specs for the Onan 3kw generator.  It doesn't say the requirements for starting it, but does say that if you buy Onan's starter battery option, the battery they supply is a 460 cold start cranking battery at 0 degrees Fahrenheit.  BUT, with the ignition on, the lead from the engine battery goes through a 40 amp breaker and then to the generator starter.  That's according to Keelhauler's latest wiring diagram.

You need less than 40 amps to crank the generator.   And to me, that makes sense, because the generator engine is a single cylinder 4 cycle engine that really doesn't take much to crank.  I would not have a problem starting it with a pull starter.  I was able to start my 8 HP single cylinder 4 cycle snow blower by hand.

it sounds like Cummins/Onan has had the question come up before.

I looked in the installation manual for my model (QG 4000 KY-R) and I only see mention to size the cables based upon distance and using 1000ccA as a guide.

Based upon the numbers stated, one 100Ahr battery ought to be able to start the generator. Makes you wonder why Battle Born says 2+. It could just be a generic safe answer.

I didn't know they put the breaker at the back of the battery compartment. It can't be seen in mine as battery cable lengths only allow the battery slide out about 4 inches. It's good to know as I wondered where it was.

I did send a note into Cummins. It will be interesting to see if they reply and what they say.

..Mike