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Duaner

Going through alternators

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Our 1986 escaper has gone through so many alternators. Someone finally tried to solve the mystery and said we should replace our electronic isolator (correct name?) with a continuous duty solenoid. But, when we asked a RV repair shop to install one, they didn't, they just installed a new fancy version of what we had. Then they said the alternator isn't showing any charge (which was the problem we were trying to address). Since we had 2 new alternators installed in the last 2 weeks, perhaps the continuous duty solenoid is in fact what we need. But, is it true that if we get that, the car battery will be subject to discharge by the camper lights, etc?  This mystery has been going on for years, the longest an alternator has lasted is 3 years once.  Thanks for any help!

Sandy & Duane

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Maybe missing a circuit. If you have the diode type isolators - for Toyotas need to have 4 terminals. 3 large for Bat1, Bat2, Alternator output and #4 is the exciter circuit which connects to a 12 hot when ignition is in run position. Without that exciter circuit no output with a diode isolator. The alternator needs to see 12vdc on its output terminal before it will produce output and the exciter circuit gives the output terminal that 12volts. If you have a 4 wire isolator check that #4 the exciter circuit has 12 volts when the ignition is on. The relay type isolators do not need the exciter wire as the battery is connected to the alternator directly and the solenoid actually connects the batteries in parallel when the ignition is in the run position.
There is another type called the seperator. I installed one after my diode type failed and blew up my alternator. Here is a link for comparison http://info.waytekwire.com/blog/battery-isolators-vs.-separators-whats-the-difference
The seperator I had was high tech. Only connected when the coach battery needed a charge and had a everything is OK led that installed on the dash. I have no idea how to troubleshoot a seperator.

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I installed a simple solenoid isolator. It’s rated for 80 amps and costs about $20. I went through 2 high end diode isolators before switching to the solonoid.

For my hookup I cut the alternator output wire going to the truck battery and joined both ends to the BAT1 terminal with ring connectors. BAT2 goes directly to the coach battery. The exciter contact lug gets power from any hot wire with ignition on. There is also a grounding lug that goes to any metal ground. With this hookup you’re not dependent on alternator output to power the isolator. Very basic, but works well for me. With the ignition off, your truck battery is separated from the coach battery. It’s been working fine for over 3 years. 

Edited by fred heath

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Yeah I think Greg means combiner that is a fancy relay type isolator that reads both batteries voltages and combines the batteries as needed basically a "smart" isolator. The missing exciter wiring can cause alternator failures or an internal failure of the exciter diode inside the isolator. I prefer a common relay type because if it's simplicity and no need of alternator rewiring.  

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13 hours ago, WME said:

Yeah there are several out there they read battery voltage not just turn on with the key. They are bi directional most of them start the cycle by charging the truck battery first once it's up then combines and charges the coach battery, once the RV is plugged in the flow reverses and charges the truck battery too. This ideal came from the boat industry as do many innovations like that but it's perfect for RV's.

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Someone told us to get a continuous duty solenoid. Is that different from the isolators & separators? Am I OK just asking for that? Is there any  big

disadvantage. We were told that with that we will need to replace our back battery regularly, keep it in good shape.

Thanks again! 

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