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Old 04-21-2006, 10:03 AM   #1
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canton , tx
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What's killing my starter battery????

Took a 2 day boondocking trip. Used the dc refer all that time. Time to go and all batteries dead. Is something wrong with the isolater? I thought draining the house batteries would not drain the starter. The starter battery has a cut off switch. Will cutting off the neg cable at the battery cure the starter drain while i try to find the source of the problem? Any other suggestions??? thanks for any help...joe...

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Old 04-21-2006, 06:32 PM   #2
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The motorhomes seem to have a chronic problem with killing the starter batteries. Both my '86 345 and '83 310 would do it. I had to either keep a little trickle charger on them, or disconnect the battery when it was parked. Never did figure out what caused it.


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Old 04-21-2006, 07:00 PM   #3
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You are correct in assuming that the isolator's function is to keep the starter battery 'isolated' from the house batteries to prevent discharge. You might have an inverter problem if your isolator checks out as the charger side of the inverter might be linking the 2 systems.

You might consider a battery cut-off switch for the starter battery as a cheap and fool-proof way to separate the 2 systems in the future.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
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Old 04-22-2006, 09:03 AM   #4
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canton , tx
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Thanks for the help. How do you check the isolater and inverfter? Lew, I have a battery cut off switch and will use for sure. joe
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Old 06-19-2006, 05:28 PM   #5
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, Alaska
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Pesky little battery drain

A while back I was frustrated because my starter battery would drain after a couple of days sitting. I searched high and low for a cause and finally found it! Each time my motorhome door closed, the step switch would draw power. When the door was left open there was no drain. I still don't know the problem, but now each time I leave the motorhome with the door closed (for long periods) I unplug the fuse for the door stair. Once unplugged the step automatically disengages for entry or exit. I am always sure to put the fuse back (the stair will raise) before hitting the highway.
It doesn't seem right that my stair draws power when in the up position. I have yet to find what the problem is, but at least I can avoid the power drain for now.
Anyone have any ideas on how the stair switch is supposed to operate?
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Old 02-28-2007, 05:29 PM   #6
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Mercury switch (???)

Anyone have any ideas on how the stair switch is supposed to operate?

While under our rig awhile back, I thought I remember seeing a small mercury switch fastened to the step. I though this was only for the indicator lamp on the dash (it is on if the ignition is on and the step is down). If I hit a large bump, the light would coem on briefly, then go back off. Our step is operated by engine vacuum, when the engine goes off, the step goes down. When the engine is started, the step goes up.

Not sure if this helps narrow down the slow drain on the chassis battery...I know mine does this also.
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Old 02-28-2007, 06:35 PM   #7
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1969 25' Tradewind
1983 34' Limited
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I used to work on vehicle electrical systems in the 80,s and 90,s. I always found that what ford was using for charging systems was the answer for every way to islate a charging system for the auxiary battery. They used a continuous duty relay. It looks just like the starter relay usrd on the ford starter. It is mounted on the firewall and is very easy to wireup. It just 2 connections for a batt connection and a terminal for engaging the switch. I found that this system worked very well. I just don't trust diodes that much. If your not checking them out with a diode capable multimeter all the time its hard to tell if it is working. I would put a switch between the starting battery and the other part of the system connected to a toggle swith or press button. my old winnebago had this setup.
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Old 03-09-2007, 06:30 PM   #8
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I have MH in storage, went to visit it and the step was down, thought that was strange maybe someone tried to break to it or something, nope doors locked , then got in and tried to start it and nothing, hit the aux start started up and the step went up.
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Old 03-09-2007, 06:57 PM   #9
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Ours also had several draws on the starter battery which we isolated. The tag axle brake was wired in hot and always on, the radio is wired to the car battery so if you have it on a lot that is also a drain. We no longer have a problem. We did try the screw on battery post disconnect but they are made of very cheap metal and both broke, one at the border crossing at Mexicali and one on the downgrade out of San Luis Obispo. Both times we found out when we tried to start the generator and the drain killed power to the Moho because it was only running off the alternator. We have not had a problem in over a year The step is meant to stay down when parked until the unit is running--we are going to a kwikee 2 step which has a different set up.

Ron and Debbie Lawrence
1985 345 Motorhome...... delightfully tacky......yet unrefined
AIR 7992
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