Generator start battery

[jelmore]

Thanks Harry. I'll bet that's what the problem is.

I asked Vanner how to test the isolator. I told them what Liberty told me, that the battery is charged from the alternator. They said to check voltage on the battery side and compare to the other side when the engine is running to see if alternator current is passing through. There should be a -.4V to -.7V or so difference.

I checked it with the engine NOT running and surprise, surprise ... battery side was 10V and the other side was 13.5V. Checked the 12V alternator and it reads 13.5V. I know the 12V alternator charges the house batteries, and the house batteries are at 13.5V, so there must be a connection to the house batteries through the alternator, and the isolator must be an isolation between the house batteries and the generator battery.

If the isolator was working, I would think there would be a similar voltage on both posts. The isolator failure must have happened months ago and that caused the new generator battery to get used up. Since it is at 10V, I'd guess it's all used up and wouldn't take a charge if the isolator is replaced.

Does any of this make sense or am I imagining things?

[Jon Wehrenberg]

Jim,

The Liberty response to you troubled me until I got home and read this thread again.

I stand by my original response.

All charging sources on our buses also charge the generator battery. Inverters, generator alternator and engine driven alternator as is the case on my coach as well as yours.

[jelmore]

Just before I ordered a new isolator, I called Tony back to run my voltage readings by him. Then, he said he didn't really know how it was set up, that this topic was really Bill's department.

So, lots of discovery on my part. Thanks for all your experience. I think I'm starting to get some of this 12V business.

[Jon Wehrenberg]

Jim,

No disrespect meant to owners, but one thing is for sure. Advice specific to a particular converter, and specific to a particular model from the converter needs to come from either the converter or someone knowledgeable about your specific converter and coach model.

The so called mystery of our 12, 24 and 120 volt systems is not that difficult to understand, especially when we learn how to monitor our systems and we get to develop an understanding of what our coach gauges and displays are telling us.

When your repair is made, monitor your generator voltage gauge under various conditions such as alternator running via the generator motor, via the bus motor running, via the inverters charging the house (such as when on shore power) and with nothing running and the bus not connected. I am sure you will quickly learn exactly what maintains a charge on your generator battery. From that point, isolating the problem is simple. (Not intended to be a play on words)

[jelmore]

Well, little did I know that the information I got from Liberty Coach was wrong. How in the world would I know? If not for this forum, I would have been replacing generator start batteries every 4 months. Thanks to all. When I get the new isolator in, I'll hope I'll be able to confirm that all is well as it was on Harry's coach.

[Jon Wehrenberg]

Jim,

All that isolator is intended to do is to pass the charging current through to the generator battery, but not to allow current from the generator battery to flow back to batteries with lower voltage, such as house batteries that may need a charge. That way the battery will have starting voltage when you need to start the generator to recharge the house batteries.

I have never followed the wiring backwards so I do not know the specific origin of the incoming charging voltage sources. They may come to a common point or they may be a single source such as house batteries which are charged via the bus alternator and the inverters, and thus are both capable of charging the generator battery.

The isolator may be checked for continuity via an ohmeter which should show current can flow in one direction and not the other, and then a voltmeter to show current on the input side is in fact flowing through to the battery side.

I will stick my neck out a mile here and predict you may find the generator alternator is not putting out charging current because I cannot imagine that the alternator output will be fed into the input side of the isolator and thus back to the house batteries. Let me know. I will have egg on my face if I am wrong, but I am curious.

[dalej]

you may find the generator alternator is not putting out charging current_Jon

Why would a coach set up this way have a generator alternator? I don't have one and it makes sense. Your house batteries and generator battery (I have one) are charging going down the road or while parked and plugged in or the generater is running and the inverter is charging them.

[Ray Davis]

******Status, In the barn. Last trip 9.11-17.09 POG

Hey Dale, that was a long trip! 8 months? What month is the 17th month anyways?

Ray

[dalej]

Sorry, I thought it looked like Sept. 11-17 of 09

[Ray Davis]

Sorry, my bad. I mis-read it!!