bufbooth Posted November 5, 2016 Share Posted November 5, 2016 Hello All, was hoping to get some help on a possible bad Battery Isolator. I believe it is original on my 1990 Toyota. My battery is only getting 11.76 volts, I believe it should be about 14.5 volts. The battery isolator has four wires/nuts on it, going left to right I get the following: Nut1: 12.52 volts (the wire on this runs to the coach battery), Nut2: 14.7 volts, Nut3: 14.7 volts, Nut4: 11.65 volts. Should Nut4 be kicking out 14.7 (or so) volts instead of 11.65 volts? I am guessing Nut4 is supplying the volts to the engine battery, is that correct? Thanks, Dennis... Quote Link to comment Share on other sites More sharing options...
Bob C Posted November 5, 2016 Share Posted November 5, 2016 Does the isolator have a wiring diagram printed on it? I had a similar isolator on my '88 Escaper when I bought it and it was dead at that time. If I remember correctly, the left bolt is power to the coach battery, #2 is power from the alternator. #3 was the trigger voltage that put power from the alternator to the coach. #4 was power to the engine battery. My problem was no power to the coach. I think that your isolator is shot if the voltage on all of them are not the same. I replaced mine with another solid state isolator and it crapped out after only 4,000 miles. i have since replaced that one with a solinoid type isolator and have put 15,000 miles on it. I also installed a volt meter in the cab that reads the coach voltage. i now know if I am charging my coach battery at a glance. It cost me about $10 to put in but it gives me piece of mind knowing that I will have a charged battery when I need it. Quote Link to comment Share on other sites More sharing options...
bufbooth Posted November 5, 2016 Author Share Posted November 5, 2016 I also noticed that the wire off of post/nut-1 (that goes to the coach batter) goes into an in-line breaker. I was thinking I would replace the in-line breaker (they are only $3) too, if I had to replace the isolator. I cannot tell what amp rating is on the current breaker, they come 15 to 50amp. Any idea what size In-Line amp breaker should be for the power going to the coach battery? Quote Link to comment Share on other sites More sharing options...
linda s Posted November 5, 2016 Share Posted November 5, 2016 On Sunraders they are 30 amps Linda Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 5, 2016 Share Posted November 5, 2016 (edited) They should be marked 1 and 2, A and E. 1 and 2 are the battery leads it does not matter what battery is connected it will work the same. A is the lead from the alternator E is the exciter it is a power source from the key switch. This is what you need to know. The leads 1 and 2 should be pretty close in voltage with the engine running the A lead is from the alternator it will be a bit higher E should have 12 volts with the key on. Yes it is possible the isolator is toes up if the battery voltage is low find out what battery is low one will be, that will tell you that the isolater is not passing a charge voltage to that battery. If the battery was installed backwards it will take the isolator out pretty much right away. The breaker will most likely be 30-35 amp it's doubtful it's bad or you would have no voltage. Edited November 5, 2016 by Maineah Quote Link to comment Share on other sites More sharing options...
bufbooth Posted November 6, 2016 Author Share Posted November 6, 2016 This is my Islolator, a Sure Power 9523A https://www.waytekwire.com/item/80066/?gclid=CJjCm8rQyMMCFcRQ7AodKgcA-Q Pole-1 has 12.52 volts, Pole-2 has 11.65 volts, Pole-A has 14.7 volts Pole-E has 14.7 volts. And Battery is 11.76 volts. Last week the battery was getting 13.6 volts. Looks like Pole-E is getting too much voltage (14.7 vs 12) and Pole-2 is not getting enough volts (guessing it needs to be over 12 volts). Since Pole-E is getting too much voltage, does that pretty much prove that the isolator is bad? Dennis... Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 7, 2016 Share Posted November 7, 2016 No, forget about the "E" terminal if that has power it makes the alt work that's it. Have you had problem starting the truck? Have you had problem with the coach lighting etc? Check the voltage at each battery with the engine off see what they read then go back to the isolator with the engine off and see what 1 and 2 read if they come close to matching the battery readings replace the isolator. I'm not real fond of solid state isolators but if that is what you have that is the type you need to replace it with other wise you'll have to do some rewiring. Quote Link to comment Share on other sites More sharing options...
Totem Posted November 11, 2016 Share Posted November 11, 2016 I had/have identical isolators. When i went through a string of bad alternators they cooked my original isolator which in turn may have lead to frying some of the alternators. Moving forward, I will always replace both at same time or at the very least verify proper alternator functionality prior to suspecting the isolator by removing it from the picture and testing the alternator first. Quote Link to comment Share on other sites More sharing options...
Totem Posted November 11, 2016 Share Posted November 11, 2016 also when my isolator went bad, upon close inspection after removing it, it was clear things had failed inside it; the black goo that they pour over the posts to seal it up was bulbous and swelling in places where overheating of parts inside had occured. I would check for that also if its under suspicion. Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 12, 2016 Share Posted November 12, 2016 An alternator will not kill an isolator , an isolator will not kill an alternator with out some sort of catastrophic failure. Diodes fail open in 99.9% of the time meaning one or the other battery will not charge if there is a short in one battery system or excessive load it probably will trash the isolator because they are only capable of sinking so much current. They have fins on them for a reason they are less than 100% efficient the loss becomes heat. One of the better ways to kill an isolator is connecting a battery backwards. Isolators are not smart they do not control voltage they do not regulate they only pass current in one direction nothing more there is nothing inside that is grounded so it can not short. You can not remove the alternator from the isolator with out providing a voltage to the B+ it comes from the isolator (E terminal) once the voltage is applied with no battery connection there is a chances the alternator will go full charge causing issues with the alternator regulator do not do this. Quote Link to comment Share on other sites More sharing options...
bufbooth Posted November 12, 2016 Author Share Posted November 12, 2016 Funny that alternators came up, the last time I had the Toyota out (last Fall), the alternator went bad. I tested the alternator at that time (myself and the auto part store) and it was bad. The isolator might of been bad then and I that I just did not notice it yet. Anyway, I found the identical model isolator, I should get it in a couple days. Thanks all... Quote Link to comment Share on other sites More sharing options...
Totem Posted November 14, 2016 Share Posted November 14, 2016 indeed, bufbooth, your story sounds very similar to mine. I disagree with Maineah on this one. In my world, any circuit can ruin anything in it if something fails. bad voltage regulator could in theory push something to the isolator that it doesn't like. I supposed a third killer not mentioned would be a dead battery thats working things too much or 4th, heat itself; as Maineah mentioned the fins are there for a reason but when its 110 degrees out in the desert... those fins probably aren't helping much. depends on what action its seen. I've had absolutely 0 trouble with my new isolator and alternator.. unfortunately it took 3 or 4 of them to get there (alternators). I also replaced the battery when the isolator failed for the perfect trifecta of "just in case this is bad" mentality. Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 15, 2016 Share Posted November 15, 2016 On 11/12/2016 at 2:01 PM, bufbooth said: Funny that alternators came up, the last time I had the Toyota out (last Fall), the alternator went bad. I tested the alternator at that time (myself and the auto part store) and it was bad. The isolator might of been bad then and I that I just did not notice it yet. Anyway, I found the identical model isolator, I should get it in a couple days. Thanks all... You can as long as the isolator is in place that is where the "E" terminal comes in. When an alternator is bench tested it has power to the B+ terminal and a connected battery in the tester so the "E" terminal is moot. Your reading of 14+ volts tells me your alternator is fine it's just not going through the isolator to one battery meaning it has a bad diode on either 1 or 2 terminal. Even good solid state isolators loose .7 volts just doing their job that is normal that's why they have to be cooled but a big dip it is not. Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 15, 2016 Share Posted November 15, 2016 On 2016-11-14 at 11:27 AM, Totem said: indeed, bufbooth, your story sounds very similar to mine. I disagree with Maineah on this one. In my world, any circuit can ruin anything in it if something fails. bad voltage regulator could in theory push something to the isolator that it doesn't like. I supposed a third killer not mentioned would be a dead battery thats working things too much or 4th, heat itself; as Maineah mentioned the fins are there for a reason but when its 110 degrees out in the desert... those fins probably aren't helping much. depends on what action its seen. I've had absolutely 0 trouble with my new isolator and alternator.. unfortunately it took 3 or 4 of them to get there (alternators). I also replaced the battery when the isolator failed for the perfect trifecta of "just in case this is bad" mentality. Suit your self, worst case? A runaway regulator but it is more likely to boil the water out of the battery than trash an isolator. it's the voltage not the current. A working isolator might well exceed 110* on a normal day that is not real hot 11.6* above body temp. Dead battery no big deal it will not take more power than the isolator is capable of carrying and the power all ways takes the path of least resistance. 8 Quote Link to comment Share on other sites More sharing options...
Totem Posted November 17, 2016 Share Posted November 17, 2016 110 degrees is outside, under the hood of an overworked underpaid Toyota chassis it gets hotter! Quote Link to comment Share on other sites More sharing options...
Maineah Posted November 17, 2016 Share Posted November 17, 2016 It does not matter all of them are under the hood. Toy Home's are just a small percentage of MH's using them. A huge V8 in a 40' motor home works just as hard and makes more heat they can take it. Quote Link to comment Share on other sites More sharing options...
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