boschat Posted March 22, 2018 Share Posted March 22, 2018 I have a 1989 Toyota Odyssey RV with a V6 in it. The battery isolator is a 4 terminal solid state type and puts out 15.5 V to the house battery wire when not connected to the battery, but as soon as I connect the wire from the isolator to the battery the voltage drops to 12.33 V (i.e., the voltage of the house battery itself). As a note, the wire that runs to the house battery 1st goes through a 30 amp breaker. 1) What the heck is going on with the isolator when I hook it up to the house battery?! The truck battery charges just fine when the engine is running, reading 14.5 V at the battery terminals. 2) Assuming I need a new isolator, what model do I buy, I can't find anything similar on the net and all of the lettering is gone off the one in the engine compartment. Quote Link to comment Share on other sites More sharing options...
WME Posted March 22, 2018 Share Posted March 22, 2018 Long distance electron chasing is just way to much fun. What happens to the truck battery v when the house battery is disconnected? Can you borrow a known good 12 battery to install to check v with. There a herd of possibilities so just take small steps and keep track of the results. Quote Link to comment Share on other sites More sharing options...
boschat Posted March 22, 2018 Author Share Posted March 22, 2018 The truck battery reads 14.5 V when the house battery is disconnected. The house battery is brand new so I know its good. Do you know what solid state isolator I would need> Quote Link to comment Share on other sites More sharing options...
WME Posted March 22, 2018 Share Posted March 22, 2018 (edited) Not logical The isolator can not increase the voltage. Ok any 4 post isolator will work. https://www.ebay.com/itm/Sure-Power-Battery-Isolator-70-Amp-2-Battery-702-D/232344206760?epid=702441896&hash=item3618cb3da8:g:cqAAAOSwhzRaX0YT&vxp=mtr Here is a different take on things...https://www.ebay.com/itm/Victron-Cyrix-ct-12-24V-120A-Intelligent-Battery-Isolator-Combiner/253501876542?epid=2256124828&hash=item3b05e3a93e:g:yJcAAOSwdGFYpx3Q The combiner will allow your 12v converter to charge the truck battery and the house battery when the RV is plugged in to 110v. It will charge the house battery when the truck is running. It acts as an isolator when parked and nothing is plugged in. Edited March 22, 2018 by WME Quote Link to comment Share on other sites More sharing options...
boschat Posted March 22, 2018 Author Share Posted March 22, 2018 (edited) Completely bizarre. Makes no sense to me either. Clearly a switch can't increase the potential...I don't know what's going on with the thing. OK, I'll pick up one of those 4 terminal solid state isolators and a new 30 amp circuit breaker and hopefully that will solve the problem. PS: the #10 terminal on the isolator is for the ignition wire yeah cause I know that Toyota alternators need a feedback or something to that effect? Edited March 22, 2018 by boschat Quote Link to comment Share on other sites More sharing options...
Derek up North Posted March 22, 2018 Share Posted March 22, 2018 1 hour ago, boschat said: The house battery is brand new so I know its good. This is unfortunately not a safe assumption. Quote Link to comment Share on other sites More sharing options...
boschat Posted March 23, 2018 Author Share Posted March 23, 2018 (edited) I just bought a 90 amp solid state isolator (its a NOCO IGD 90 amp 4 terminal solid state isolator) at the RV store that is similar to the one suggested in the link above along with a new 30 amp breaker. Interestingly, in the installation manual under the "Electrical Tests" section it says that house battery terminal should read between 14.8-15.5 V and the truck battery should read between 13.8-14.5 V when the engine is on. I just finished installing it and it does the same exact thing as the old one. So what the heck is going on when I connect the house battery wire from the isolator (which reads 15.5 V when not connected) to the battery (dropping the voltage to 12.8 V)?! I have no idea what to do at this point. Edited March 23, 2018 by boschat Quote Link to comment Share on other sites More sharing options...
linda s Posted March 23, 2018 Share Posted March 23, 2018 Wire to the house battery might be broken and grounding out somewhere along the line, draining batt instead of charging. Linda S Quote Link to comment Share on other sites More sharing options...
boschat Posted March 23, 2018 Author Share Posted March 23, 2018 This is not the case Linda S because if I remove the wire coming from the isolator from the house battery it reads 15.5 V. When I reconnect it to the battery it reads 12.8 V. The wire is not grounding out anywhere. Does anyone know, is there a regulator somewhere along the way from the isolator to the battery that somehow senses that the battery is fully charged and stops the isolator from sending a charge (full charge for most deep cells results in a 12.8 V reading)? I guess one experiment I could run would be to partially discharge the battery down to say 12.3 V and then see if the voltage would increase at that point upon starting the engine. Quote Link to comment Share on other sites More sharing options...
WME Posted March 23, 2018 Share Posted March 23, 2018 (edited) There is only 1 regulator in your 12v system it is in the alternator. So small steps. Disconnect the house battery. Take the wire from the alternator (A?) and install it on the truck battery post. What your doing is make a stock truck system. Check the voltage 13.5-14.5v with the engine running. If thats OK, then do the same for the house battery, alternator to house battery, no isolator. Check voltage at the bolt and at the battery again with the engine running. Dont worry about not charging the truck battery, it will run for at least 1 hr. As Derek implied new don't mean good. The math behind that is a normal charging voltage is 14.5v at the battery with the engine running. A shorted cell will drop 2v. So 14.5-2=12.5 which is very close to whats happening to you. Remove the house battery cables and let it rest for a couple of hours and then measure just the battery v. Resting v is 12.8-12.9. 12.4v means 50% charged. Below 11v is bad cell Edited March 23, 2018 by WME Quote Link to comment Share on other sites More sharing options...
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