Boondockit Posted September 20, 2016 Share Posted September 20, 2016 Hi, this is my first post, I have an 83 Minicruiser and I'm not sure it has a back battery (I've looked everywhere) When I run the engine I get my 12v stuff in the coach going (lights, fans etc), when I turn off the engine I can use them for a bit (with engine off) but they eventually die down, since I can't find a back battery, is the coach stuff running off my engine battery? (with engine off) if so can I drain the engine battery by leaving a fan on? (In coach) I notice that when I go back to the coach a few days later (engine off) that I don't have any coach stuff working but engine battery turns right over (and the coach stuff comes on again)....only to be dead again until I fire the engine back up... i don't have have a wiring diagram (does anyone?) but given the issues, can anyone enlighten me? Thanks so much! Michael in Iowa Quote Link to comment Share on other sites More sharing options...
Derek up North Posted September 20, 2016 Share Posted September 20, 2016 It sounds like you have a 'house' battery' somewhere. Quote Link to comment Share on other sites More sharing options...
zero Posted September 20, 2016 Share Posted September 20, 2016 8 hours ago, Boondockit said: Hi, this is my first post, I have an 83 Minicruiser and I'm not sure it has a back battery (I've looked everywhere) It is a Mark 5, Mark 6, or Mark 8? Did you look under the couch-bed? I've worked on 1985, 1986, 1987, and 1988 Minicruisers. They all had rear mounted batteries. My 1988 has an outside door on the driver's side to access the battery box. But mine is a Mark 19 that is 19 feet long. Your's ought to be 17 feet long and as I recall, the rear house battery is inside the coach somewhere. Look under the hood and see if there is a battery isolator. If so, just follow the wire from it that runs to the back. It has to lead to the house battery IF you have one. Note - the 1984 Nissan Minicruiser I had also had no power in the "house." I found the battery in a plastic vented box under the couch-bed and it was cracked and stone-dead. Here is a photo under the hood of a 1979 Minicruiser. I marked the battery isolator. Wire on the right is what runs back to the house battery. Quote Link to comment Share on other sites More sharing options...
zero Posted September 20, 2016 Share Posted September 20, 2016 Here is the original isolator on my 1988 Minicuiser (I removed it and replaced with a relay). Quote Link to comment Share on other sites More sharing options...
Boondockit Posted September 20, 2016 Author Share Posted September 20, 2016 Oh gawd, yes you're all right, when I originally looked under couch/bed there was a white airtight looking box with flex hoses coming out of it, (it looked like a water pump or something like that) of course inside is the battery which I am testing now...thanks to all for taking the time to help and solve... What would be the benefit of swapping a relay for the isolator? (Jdemaris) Quote Link to comment Share on other sites More sharing options...
zero Posted September 20, 2016 Share Posted September 20, 2016 A relay cannot blow like an isolator can. An isolator will blow just like a fuse when enough amps go through it. Also there is no voltage loss with a relay. All rectifier-type isolators have around .6 or .7 of a volt of loss. That is a lot when you consider just that long run from the front to the rear already has loss. I would not be surprised if your isolator no longer works. Many I find on older RVs are blown. Easy to check with a voltmeter or continuity checker. Quote Link to comment Share on other sites More sharing options...
Boondockit Posted September 21, 2016 Author Share Posted September 21, 2016 4 hours ago, jdemaris said: A relay cannot blow like an isolator can. An isolator will blow just like a fuse when enough amps go through it. Also there is no voltage loss with a relay. All rectifier-type isolators have around .6 or .7 of a volt of loss. That is a lot when you consider just that long run from the front to the rear already has loss. I would not be surprised if your isolator no longer works. Many I find on older RVs are blown. Easy to check with a voltmeter or continuity checker. Thanks, can you recommend one or link one to me here in particular? (Relay that you like)...best... Quote Link to comment Share on other sites More sharing options...
zero Posted September 21, 2016 Share Posted September 21, 2016 You can get a simple relay or a "smart" relay. Relay must be rated for "continuous duty." A simple relay is just a switch that is remotely turned "off" or "on." In the case or your RV, it gets hooked to an ignition wire. This way - any time your ignition key is "on" the relay also turns "on" and connects all the batteries together so they both charge. When the key is "off", the relay opens and the two batteries are separated. This way, when parked and the engine not running, you can use the "house" battery without worrying about draining the "cranking" battery under the hood. A "smart" relay does not need to be hooked to an ignition wire. It senses voltage and turns "on" and "off" automatically. When you first start the engine - the "cranking" and the "house" batteries are separated and only the "cranking" battery gets any charge. Once it is fully charged and its voltage rises above 13.8 volts - the relay automatically turns "on" and combines the "cranking" and "house" batteries. Then the "house" gets charged and once that is done - both get maintained. When you turn the key "off", they stay combined for a little while until voltage drops a little and then the relay opens and turns "off" automatically. The higher the amp rating, the longer the relay is apt to last. I use the Trombetta listed for $18.95. Mine is sort of a "hydrid." I used that Trombetta and then got just the control chip from Powerstream so mine is now a "smart" relay. Powerstream will sell just the control chip instead of the complete relay/chip unit if wanted. Quote Link to comment Share on other sites More sharing options...
zero Posted September 21, 2016 Share Posted September 21, 2016 Here is what that Trombetta relay looks like under the hood of my Minicruiser with the Power-Stream chip wired into it. Quote Link to comment Share on other sites More sharing options...
Boondockit Posted September 23, 2016 Author Share Posted September 23, 2016 Wow = thanks a lot... Quote Link to comment Share on other sites More sharing options...
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