Difficulty starting generator... batteries? Converter?

Ye olde 1993 Southwind demonstrated an odd problem last week - the generator would not start, just a stuttering from the starter solenoid. I found that (oddly) starting the engine allowed the generator to start readily... I'm assuming with the engine running current from the alternator was sufficient to overcome a battery deficiency?

This weekend, same problem. This time I hit the "aux start" button to bridge electrical systems and, again, the generator fired right up. So, it does seem like for whatever reason the house batteries lack the oomph to start the generator.

Both house batteries are only a couple years old and are generally well treated - not discharged etc. A multimeter shows they're fine, although I certainly understand that just showing good voltage isn't the full story. But, I am not 100% convinced they're the sole issue.

The converter is ancient and original - a Magnetek 50a "Series 900 950-2" - and could also factor in here. TBH I have been looking for an excuse to replace it, and this may be that moment for me. It is possible it has slowly murdered these batteries, although I'd expect to see side effects of weak house batteries elsewhere and I don't.

We mostly use this rig for boondocking, day trips, etc. We are rarely connected to services. We don't use appliances, we rarely use the HVAC. The reason I found these problems is random - last weekend was the monthly "run systems check" and this weekend was "we are out, why not." The generator wasn't needed either time.

We only have two batteries, though I keep thinking about getting two more... for no good reason, we aren't having problems with what we've got now.

Anyway, I'm looking for both a recommendation on a replacement converter and any thoughts on angles I may have overlooked in diagnosing this non-start issue.

Thanks!

Edit - the generator is an ancient Onan 4000, so the starter is suspect, though I dont know what three batteries could really do than two couldn't. The starter solenoid is only a couple years old.

The stuttering starter indicate low voltage there, so either weak battery or corroded connection(s). Running the engine increases the voltage (alternator), so overcomes the problem. You need to ascertain whether the genset starts from the house of engine battery, to make sure you are verifying the tight source. I don't know which was used back in 1993, but nowadays most use the engine (chassis) battery.

The old Magnetec 950 either works or does not. If it is charging the house batteries, you can't ask for anything more. If the Magnetek can produce 13.3-13.6v at the house battery, it's ok (but I would have a newer, multi-stage charger on my wish list).  Note, however, if the genset starts from the engine chassis battery, the Magnetek is irrelevant.  However, you can use the Aux Start or Booster switch to momentarily couple the house battery to the engine battery and get some assist that way,

We had a similar situation on our Four Winds while on the road. I couldn?t find a logical solution ( Sorry Spock) so had to call in a repairman. He crawled underneath with a crescent wrench and a wire brush and cleaned a stud where all the positive battery cables came together. $200 dollars later we were back on the road. Just a thought.

Gary RV_Wizard said:

I don't know which was used back in 1993, but nowadays most use the engine (chassis) battery.

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I would not have anticipated this, but it does make sense and would explain what I am observing. Seems like I will need to do a deeper dive into the engine battery!

Another maybe pertinent detail - after running the generator for about an hour the house batteries are virtually discharged 10 hours later. I am sure this indicates the batteries themselves are in bad shape, but also something murdered them.

AN hour is no where near long enough to charge the house batteries. SIX Hours.. IF your converter is the proper size (30% C/20) is the minimum recharging from 50% SOC.|

Longer if you have increased battery capacity.

Primarily boondocking and rarely plugging into shore power indicates a high risk of premature battery failure and a reduction in the quality of life while they are functioning. Motors will draw higher amps at lower voltages resulting in higher temperatures in the motor. If the generator is found to be starting off the house batteries, using the momentary switch for generator starting, as a rule, would be a healthy choice even if a problem is located in the cabling.

Have you explored adding a solar charging system?

I don't know which was used back in 1993, but nowadays most use the engine (chassis) battery.

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Industry practice (and later, standards) have flip-flopped on this a couple times. Back in the early-mid 90's, the genset often had its own battery. Then some began using the house battery to start it (a cost savings).  Then the RVIA standardized on the chassis battery. As I understand it, the thinking is that the house batteries get run down while boondocking but the chassis battery(s) is isolated and still has power to start. Plus you can always use the Aux start to boost the chassis battery if needed to get the genset going.

Henry J Fate said:

Primarily boondocking and rarely plugging into shore power indicates a high risk of premature battery failure and a reduction in the quality of life while they are functioning.

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I think there may be a misunderstanding... we don't use electricity at all. Historically, the singular solar panel has been more than sufficient to keep the batteries at 100% pretty much all the time. When not in use, the RV is connected to mains at all times. There is no (good) reason for this behavior.

Gary RV_Wizard said:

Industry practice (and later, standards) have flip-flopped on this a couple times. Back in the early-mid 90's, the genset often had its own battery. Then some began using the house battery to start it (a cost savings).  Then the RVIA standardized on the chassis battery. As I understand it, the thinking is that the house batteries get run down while boondocking but the chassis battery(s) is isolated and still has power to start. Plus you can always use the Aux start to boost the chassis battery if needed to get the genset going.

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Can you guide us to the actual RVIA standard that states which battery the generator will start from? Inquiring minds want to know.

Gary RV_Wizard said:

Industry practice (and later, standards) have flip-flopped on this a couple times. Back in the early-mid 90's, the genset often had its own battery. Then some began using the house battery to start it (a cost savings).  Then the RVIA standardized on the chassis battery. As I understand it, the thinking is that the house batteries get run down while boondocking but the chassis battery(s) is isolated and still has power to start. Plus you can always use the Aux start to boost the chassis battery if needed to get the genset going.

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After some further thinking, I am pretty sure the generator starts from the house batteries. Both last weekend and this weekend trying to start the generator killed the memory on the stereo, which is connected to the house batteries when the engine isn't running. I will do some further investigation, but I'm virtually positive that's the case.

We drove home last night, which was about 20 minutes... not very long. This evening, the house batteries show a combined 12.7v. When plugged into mains, they show 13.2v. The converter is audibly humming as it normally does.

Bit of a mystery. I'm really struggling with how yesterday's dead batteries became today's charged batteries.... 20m of driving and ~12 hours of sun shouldn't do it. I guess they could have developed a massive problem between February (last tested/used) and today, but it seems weird.

I'm not so convinced the converter is the source of the problem, but as observed it'd be beneficial to replace it anyway so I think I probably will.

Edit: Anyone know what this device is? It looks like it's connected to a 12v ground junction only - the black bus bar on the left.

https://1drv.ms/u/s!AqwvoBt9ZBp2gpEx1SaLgcmnmF1XWQ

Consider increasing your solar ability and make sure the solar system you have now is working properly. The converter could be tired. 13.2 volts seems on the low side but check the specs to see what is expected. The engine alternator is a very good charging source and could put a fair amount of charge in the batteries during  your 20 minute drive.
To get an accurate reading of battery voltage, all charge devices should be disconnected for at least 30 minutes or you will see a higher reading than what is really there.

Replacing the converter is an option given the age however, this may not solve the problem. I would first confirm the condition of the batteries. I tried to view the picture file you posted but it's not loading at this time. Hopefully another member can get to it.

Can you guide us to the actual RVIA standard that states which battery the generator will start from?

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That and many other aspects or RV construction are covered in the set of standards determined or referenced by the RVIA.  Members are required to follow the standards, as evidenced by the RVIA seal on each RV.  Unfortunately, you have to buy the various ANSI documents from either RVIA or the originator, e.g. the NFPA or NEC.


https://www.rvia.org/standards-regulations/standards-compliance/association-and-ansi-standards

Gary RV_Wizard said:

Industry practice (and later, standards) have flip-flopped on this a couple times. Back in the early-mid 90's, the genset often had its own battery. Then some began using the house battery to start it (a cost savings).  Then the RVIA standardized on the chassis battery. As I understand it, the thinking is that the house batteries get run down while boondocking but the chassis battery(s) is isolated and still has power to start. Plus you can always use the Aux start to boost the chassis battery if needed to get the genset going.

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For my '05 Born Free the generator starts from the coach batteries. According to a 2017 Born Free manual, it also uses the coach batteries. I don't know what is typical for other brands.

The generator starts from the house batteries on my 2010 Winnebago Journey.

It may be the RVIA construction standards gives the manufacturer some leeway on which battery to use, but their trend in the last several years has been to say "must" on a lot of details like that that are judgment calls. A prime example is which battery bank powers the slides (it's now the chassis battery(s).

♪ 

OF COURSE the batteries in my Aero and XJR **BOTH** died today.

SHEESH!

It seems to me that it is easy to see which batteries start the generator--disconnect one of the batteries and see if the generator cranks.

Yeah, but when you're in the middle of nowhere taking things apart without a plan seems like... not good.