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Old 06-16-2019, 10:13 AM   #1
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Battery isolator problem

My engine battery and my house battery appear to be killing each other. The bus sits in the driveway for a week and both batteries are dead. Jump, charge, wait a week, repeat. Wiring seems to be ok, but when I checked the solenoid this morning, I discovered a low voltage leak to the output terminal even when the solenoid trigger is off.

Can solenoids go bad? If not, what else could it be?
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Old 06-16-2019, 10:28 AM   #2
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Every device built by man will fail.

Get a decent DMM and teach yourself to use it. Be able to locate shorts, parasitic draws, high resistance points in connections, etc
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Old 06-16-2019, 10:31 AM   #3
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Would any of the suggestions you made explain how voltage is getting across an unpowered solenoid?
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Old 06-16-2019, 11:34 AM   #4
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Does the isolator make any sound when triggered with igniton ON? I think you could even feel a movement in it if you have someone work the key and you checking.
Only way is to test with a multimeter set on ohms first with no power on, then retest for voltage with power ON.


When your bus sits you might be wise to add a battery disconnect to the ground on the house batteries to prevent drain.
Solenoids do fail with age and heat buildup so ringing it out will disclose this.
Possible you have other parasitic draws going on but testing the isolator operation would be your first step.
Does your bus have a push button for "boost" starting if the start batteries are weak?


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Old 06-16-2019, 11:39 AM   #5
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Yes, the solenoid still makes an audible click when triggered by the powered fuse wire.

With no power, the solenoid reads roughly 1.5 Ohms across the main terminals.

One thought I had was that the solenoid is rated to 65A, but apparently the alternator has a max amperage of 105A - did I simply buy the wrong one and need to replace it with a higher rated version?

Is this an acceptable battery disconnect?
https://www.amazon.com/Disconnect-Ve...e%2C129&sr=1-8

thanks
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Old 06-16-2019, 11:43 AM   #6
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That disconnect would work, but it doesn't seem to have a "removable" key, if that matters to you?
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Old 06-16-2019, 11:56 AM   #7
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Quote:
Originally Posted by bfuller181 View Post
Yes, the solenoid still makes an audible click when triggered by the powered fuse wire.

With no power, the solenoid reads roughly 1.5 Ohms across the main terminals.

One thought I had was that the solenoid is rated to 65A, but apparently the alternator has a max amperage of 105A - did I simply buy the wrong one and need to replace it with a higher rated version?

Is this an acceptable battery disconnect?
https://www.amazon.com/Disconnect-Ve...e%2C129&sr=1-8

thanks

Yes, that is one of many acceptable battery disconnects, pretty common item everywhere automotive. Made for marine generally adds to the price.


Ok, so sounds like the coil for the solenoid has continuity thru it, a good thing.
Now, do you have continuity from the +ve of the solenoid coil to either the start battery and or house battery? (with power On and OFF)
Should be no continuity with power OFF. If there is you have a bad internal plunger likely and need replace the isolator.


Yes, you could be having problems with the difference in amperage ratings although I am not positive of that at this point.


If you do happen to need an isolator, I would look at the ones with only three terminals. The make escapes me but the connections are alternator, starter and house batteries. I think it is Cole Hershee also but not positive.


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Old 06-16-2019, 12:06 PM   #8
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Quote:
Originally Posted by BlackJohn View Post
Yes, that is one of many acceptable battery disconnects, pretty common item everywhere automotive. Made for marine generally adds to the price.


Ok, so sounds like the coil for the solenoid has continuity thru it, a good thing.
Now, do you have continuity from the +ve of the solenoid coil to either the start battery and or house battery? (with power On and OFF)
Should be no continuity with power OFF. If there is you have a bad internal plunger likely and need replace the isolator.


Yes, you could be having problems with the difference in amperage ratings although I am not positive of that at this point.


If you do happen to need an isolator, I would look at the ones with only three terminals. The make escapes me but the connections are alternator, starter and house batteries. I think it is Cole Hershee also but not positive.


John
With the solenoid off, there is a voltage of about 1 V across the main terminals - this is the voltage "leak" I mentioned in my first post (sorry if that wasn't clear). That was my reason for concern that I need to replace the solenoid.

As for the 3 post varieties, doesn't the housing of those need to be grounded anyway? What's the benefit to dropping the ground as its own post?
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Old 06-16-2019, 12:20 PM   #9
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Quote:
Originally Posted by bfuller181 View Post
With the solenoid off, there is a voltage of about 1 V across the main terminals - this is the voltage "leak" I mentioned in my first post (sorry if that wasn't clear). That was my reason for concern that I need to replace the solenoid.

As for the 3 post varieties, doesn't the housing of those need to be grounded anyway? What's the benefit to dropping the ground as its own post?



That voltage leak likely indicates that there is a backfeed through one or the other of the battery systems. You could disconnect one at a time to prove that.


Yes the housing will need be grounded wherever it is mounted but that is done through the bolts or screws you use. Just make sure the metal is clean and paint free in any case. You can also connect the old ground to the isolator housing when mounting it, then you have 2 grounds in effect.
The thing is with the 3 wire isolator, you feed it directly from the alternator output. Then 2 wires out, one to each battery bank positive. So the isolator isn't triggered till the engine runs, not just when key is ON.


Do the test above and then you can decide if you have to change the isolator. You should have no continuity between the main coil positive terminal and the house or start batteries which appears to be the opposite of what you are saying.


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Old 06-16-2019, 12:26 PM   #10
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You lost me. What are the other battery systems you're referring to?
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