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Old 11-27-2021, 11:52 AM   #1
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Chassis battery voltage

Is there an easy way to test the chassis battery voltage using a multimeter without disconnecting the cables? Since they are connected to the House batteries I think it combines the voltage when testing!Click image for larger version

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Old 11-27-2021, 12:10 PM   #2
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Hi Schubi,
So you measure the same voltage on the house and chassis is this why you think they are connected ?
If this is the case turn the chassis master switch (the one in the battery bay) off. Or if you do not want to do that then disconnect one of the small wires (control circuit) for the charge bridge relay.
Next just measure directly on each battery positive and negative it’s voltage.
That should work.
Jörg
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Old 11-27-2021, 12:19 PM   #3
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Quote:
Originally Posted by Schuby View Post
Is there an easy way to test the chassis battery voltage using a multimeter without disconnecting the cables? Since they are connected to the House batteries I think it combines the voltage when testing!Attachment 349936
If I’m seeing this right, you have 8 6v Duracell GC batteries and 2 12v chassis batteries.

It looks like the ground between house and chassis is tied together at the batteries and the positives go to separate connections way at the back wall.

Test across the ground anywhere and to the chassis terminal way to the back. That will give you the voltage of the 2 chassis batteries, but if you want to test them individually you will need to take the positive to positive off between the 2.

In reality the ground between chassis and house batteries are always tied together. No matter if it’s at the batteries or if the house and chassis have separate cables going to the chassis.
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Old 11-27-2021, 12:25 PM   #4
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Take a voltage measurement on that large solenoid on the back.

Measure the two small terminals. IF there is voltage on one and none on the other then that solenoid appears to be combining the batteries.

That voltage may (???) come from a circuit designed to bring the battery banks together.

That circuit is driven by any source of charging voltage. Such as being connected to shoreline or the generator is running. Solar can provide the same requirment.

I do not have a schematic of your RV but the picture sure looks like that solenoid is a Trombetta that is very very common in the industry.

If you find that there is voltage on one of the small terminals and none on the other, indicating to me that is the ground terminal, you can disconnect that wire and the solenoid will drop offline.

Doing so can give you a tiny shock as the wire is disconnected so use some disposable gloves when taking it loose.

The shock will not hurt you but removing your arms from the compartment do to the surprise can leave you bleeding.
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Old 11-27-2021, 02:50 PM   #5
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Chassis battery voltage

Always nice to hear from you Jorg, yes same voltage on house & chassis batteries.

Amosnandy, yes 8-6v & 2-12v.

VCI, yes I have voltage on Trombetta left small terminal & none on the right.

All methods read 13 volts, when I plug in shore power & inverter/charger is on I get 15 volts on all testing.

My concern is when I turn the key on (without starting) the dash board reading shows 11.9 to 12.1 volts so my fear was the chassis batteries were not charging. But they do seem to be!
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Old 11-27-2021, 03:13 PM   #6
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When you turn the key on, intake air, grid heaters come on to assist the engine starting
They can draw over 100 amps, to much for your charger.

15 volts is high for your inverter/charger, should settle in around 13.6 or so.
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Old 11-27-2021, 03:17 PM   #7
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Chassis battery voltage

Quote:
Originally Posted by Schuby View Post
Always nice to hear from you Jorg, yes same voltage on house & chassis batteries.

Amosnandy, yes 8-6v & 2-12v.

VCI, yes I have voltage on Trombetta left small terminal & none on the right.

All methods read 13 volts, when I plug in shore power & inverter/charger is on I get 15 volts on all testing.

My concern is when I turn the key on (without starting) the dash board reading shows 11.9 to 12.1 volts so my fear was the chassis batteries were not charging. But they do seem to be!

Schubi,
Just checked the voltage with ignition on and I have the same 12.0V. The fuel pump shuts off by the time the actia gauge boots up but there are still other consumers pulling amps and thus the voltage drops.
I have a large solar panel to my chassis battery and with a tad of sun here and there I know my chassis is near fully charged … however it just stared it’s 4th year since manufacture.
Hope that helps
Jörg
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Old 11-27-2021, 03:31 PM   #8
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Are the 8 Duracell wet batteries and, if so, how often do you check the water levels?
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Old 11-27-2021, 03:37 PM   #9
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Chassis battery voltage

Thanks Twinboat, I think that is exactly what's happening & makes good sense. I have the inverter/charger set at 13.4 volts & will settle in at that.

Jorg, I will try that with the ignition on & suspect you a right & it will be the same as 12 volt.

The good news is all seems to be working correctly and charging as it should! I have the original 100 watt solar working great on the house batteries but the 10 watt fried potato chip for the chassis batteries collector needs to be replace.

Thank you all,
Steve
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Old 11-28-2021, 01:41 AM   #10
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Just pull out the 10amp fuse that runs the battery connect relay.
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Old 11-28-2021, 02:56 AM   #11
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Chassis battery voltage

Amazing these are all held in with one rubber bungee cord..

And the caps are primed for popping off when anything moves..

I am sure “they have been like this for years” but I would consider metal brackets.Click image for larger version

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Old 11-28-2021, 05:36 AM   #12
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With the voltage measured on the Trombetta it is clear it is activated. The solar will activate it as well when there is enough sun of course.

Twinboat has the description of what is going on.

Turning on the ignition causes a big load and obviously drops the voltage down quite a bit.

When that voltage goes down enough for long enough the Trombetta is dropped offline.

The solar charging would not likely be able to overcome the huge load nor the converter.

Your aux/emergency start button simply bypasses the circuitry that controls the Trombetta and forces it into action thus combining battery banks.

Things seem to be working but it can take a real trained eye to discover the Trombetta is failing or has failed. Often intermittently.

The contacts can become pitted and when the relay (which can get extremely hot to the touch), engages it might not land on a good portion of the contacts.

Anyone with one of those relays should consider replacing them at least at the five year mark as a matter or preventative maintenance.

You would change a filter in a heartbeat if recommended but it is like pulling teeth to get someone to toss a seemingly good electrical component.

Remove the wire on the Trombetta that has zero voltage on it and the relay will drop out so you can isolate the batteries.

You might get some interesting readings if your solar controller has dual outputs. So find that and pull fuses or whatever you need to do to remove that charging source.
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Old 11-28-2021, 10:15 AM   #13
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Thanks Steve that's easy!
Thanks Myron I replaced the Trombetta about 5 years ago and I have removed that solar fuse!
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Old 11-28-2021, 02:19 PM   #14
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Did you mean solar fuse versus source fuse?
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