Hello,
I could use some help on how to diagnose this charging problem.
Recently, on several occasions, the voltage of the house battery was declining while driving.
When things are working normally:
Dash volt meter: 13.7v
Victron battery monitor: chassis battery 14.2v
Victron battery monitor: house battery 14.2v (once it's charged)
When the house battery isn't getting charged:
Dash volt meter: 13.7v
Victron battery monitor: chassis battery 14.2v
Victron battery monitor: house battery 12.6 or below and falling
Most of the time the issue has occurred after driving for a while.
The issue has occurred from the time the engine was started.
Sometimes the issue corrects itself while driving.
Most of the time the issue continues until the engine is restarted.
If I turn on the boost switch, the house battery voltage starts climbing. If I then turn off the boost switch the voltage starts falling again. Cycling the boost switch repeats the behavior.
I have talked to Foretravel and they thought it was the boost solenoid and that I should try tapping on it the next time the problem happened. I haven't had an opportunity to do that yet. Every time it's happened has not been a good time to pull over, extend the slides, and open the hatch to get access to the boost solenoid or to take voltage readings on the battery isolator. I don't see how the boost solenoid could cause this scenario, but when I get the the chance I'll give it a tap when the issue is occurring. When I asked Foretravel if it could be the battery isolator, they said probably not, that if the isolator fails, it usually doesn't cause an intermittent problem.
Thanks much for any input.
Joe
You say when driving sometimes the alternator is charging sometimes it's not. One thing if that's
what's happening I would think sticking brushes in the alternator.
Joe,
If the boost switch functions when you flip the switch on the dash it is doing what it is made for. If the switch is in the normal position that would be off it is out of the picture as it is just there. Said another way it has no way to know what is going on as it is only a manual switch to control it.
The Isolator can do a lot of strange things and this could be one of them. One of the diodes can be failing causing intermittent charging. The isolator is the only place that the 2 battery banks are tied together while the engine is running unless someone has done some creative wiring in the past. Pull the wires off the isolator and give them a good cleaning along with checking the diodes to see if they are functioning properly. If the isolator looks like it has been hot and melted some of the epoxy then for sure I would bet the problem lies here.
With the battery voltage on the house batteries dropping that quick you may need to check the batteries to see if you have a failing battery or a corroded cable This could be causing the isolator to overheat and break down.
Mike
First thing I would check as well would be all connections alternator to batteries.
Does your 2008 have a diode-based battery isolator or solenoid-based isolator?
I am going to guess diode-based like I have.
First guess that came to mind was the isolator is going south.
Mike, coach probably has a residential refrig and the inverter is running off the house batteries while going down the road and batteries are not getting a charge from alternator. .
Like Mike says, your boost solenoid is working correctly.
I would avoid accepting electrical system advice from the FOT employee who told you to "try tapping on it".
Intermittent electrical problem often = bad cable or loose connection, most likely suspect the cable(s) running from isolator to house battery bank.
Do what Brett said - check cables for corrosion (swollen insulation), clean the terminal posts and cable connectors, make sure they are tightly bolted on posts.
Hello,
Thank you for all the feedback.
When the house battery is discharging, it's not a fast discharge. Didn't mean to imply that. No residential fridge. With the inverter running and misc. 12v draws, the battery voltage drops .1volts in a couple of hours maybe.
The isolator is a diode based, 3 post, 200 amp Cole Hersee. I don't know if it's original, but assume so.
Thanks for confirming that the boost solenoid can't be part of this issue. I'll focus on testing the isolator and cleaning and inspecting connections and cables.
If it is the isolator, since it's an intermittent problem I feel there is a good chance the isolator will test okay. If the isolator tests okay and I don't find any connection/cable problems, what do you think of the idea of switching the cables on the two battery posts on the isolator? I'm thinking if I do that and then if the next time it happens the chassis battery is the one discharging, it means it's the isolator for sure.
Thanks much you guys.
Joe
To check the diode-based isolator when voltage is down:
Engine running and at around 1,100 RPM. Check between good ground and center lug (from alternator B+). Should be in the mid to high 14's. Next, check the outer lugs (connected to the two battery banks). The readings here should be about .7 VDC lower than the center.
Hello,
I did some of the testing/inspecting. Here are the results:
Volts at the isolator: Engine off, wires connected (not cleaned yet), generator running, inverter's charger charging:
Note: In addition to the wire going to the chassis battery, that post also has a small wire connected to it. Didn't trace, but assume it's the alternator sensing wire.
Chassis battery post: 13.04v
Alt. post: 13.08v
House battery post: 14.70v
Volts at the isolator: Engine off, wires connected (not cleaned yet), generator/inverter had been off a few minutes:
Chassis battery post: 13.04v
Alt. post: 12.86v
House battery post: 12.92v
Out of curiosity, I measured Volts across isolator posts: Engine off, wires connected (not cleaned yet), generator/inverter had been off a few minutes:
Pos. test lead on chassis battery post, neg. test lead on alt. post = 0.11v
Pos. test lead on chassis battery post, neg. test lead on house battery post = 0.16v
Pos. test lead on alt. post, neg. test lead on house battery post = 0.05v
Wires disconnected and multi-meter in diode test mode:
Pos. test lead on alt. post, neg. test lead on chassis battery post = .435
Pos. test lead on alt. post, neg. test lead on house battery post = .419
Neg. test lead on alt. post, pos. test lead on chassis battery post = no reading
Neg. test lead on alt. post, pos. test lead on house battery post = no reading
No reading between ground and any of the posts when touching ground with either the neg. lead or the positive lead.
Multi-meter back in DC voltage reading mode:
Just out of curiosity, voltage of cables when disconnected:
Chassis battery: 13.03v
Alternator: Started at 12.15v and dropped to .02v over the course of about 45 seconds
House battery: 12.79v
Connections at isolator cleaned and connected:
Chassis battery: 13.03v
Alt. 12.80v
House battery: 12.79v
Engine running at 650 rpm, connections at isolator cleaned and connected:
Chassis battery: 14.48v
Alt. 15.31v
House battery: 14.46v
Engine running at 1,200 rpm, connections at isolator cleaned and connected:
Chassis battery: 14.45v
Alt. 15.27v
House battery: 14.42v
I took it on a road test the day before doing the testing, but it didn't act up.
Thanks for any input.
Joe
It doesn't seem right to me that you would have voltage at the center post of the isolator with the engine not running, but I don't know what alternator you have on your coach. I would think that if you have voltage on the center post and the house batteries go dead then it would also drag down the engine batteries. The isolator may not be the problem. You need to see why there is voltage on the center post. Has the alternator been replaced? If it has maybe a duvac alternator was not what was put on.
I would think if there is voltage at the center post with the engine off the isolator
diode is shorted out and you need a new isolator.
Thank you for the feed back. I'm going to order an isolator. According to this article, there should be no voltage on the alternator post when the engine isn't running: How To Test A Battery Isolator | RV Lifestyle (https://rvlifestyle.com/how-to-test-a-battery-isolator/) (Second to last paragraph.)
I'm confused that when the generator/charger were running (but not the engine), the alternator post voltage was the same as the chassis battery voltage, which was not being charged and thus lower than the house battery voltage. But with the gen and the engine both off, the alternator post voltage was the same as the house battery voltage, which was then lower than the chassis battery voltage. So the voltage I'm reading on the alternator post is the same as whichever battery has the lower voltage. I'm no elect. eng. so I have no idea why/how a diode isolator would behave that way. I'll just do the bad thing and "assume" it is the culprit.
Thank you everyone.
Joe
Take the alternator cable off the isolator and see if you have any voltage that way with the engine
off on the alternator post.
Good idea.
What you're seeing here is a whole bunch of electrons trapped between the diode bridge in the alternator and the diode in the diode isolator. There would have been nothing to see here if the original poster had used a cheap Radio Shack VOM, but all of the Volt Ohm Meters made today have high impedance inputs: It took long enough to see for the electrons stored in that line to bleed off through the meter. Touching a finger to the post and ground will do the same thing faster. This is why, in some instances, I suggest using a 12v light bulb as a load on a circuit under test, as a high impedance VOM, $8 at Harbor Freight, can lead you astray.
Does it make any sense to replace it with a B2B charger instead of an isolator. If you are considering Lifepo4 at a later date?
Joe,
I encountered the exact same situation (mystery voltage on isolator center post with engine off) 8 years ago. We had a rather lengthy (and wandering) discussion on this subject. You may find the thread interesting. See link below. I eventually replaced the OEM isolator as a first step in continuous upgrades to my electrical system. I will say, however, that I never could pinpoint any
specific problem that I could attribute to the fact that my old isolator always had some voltage showing on the center lug.
I DO agree that replacing your original isolator (with something...) is a wise move at this point.
Bad Isolator? (https://www.foreforums.com/index.php?topic=20662)