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Battery isolator replacement source
does anyone have a good source for a battery isolator?
Mine needs replaced.
I was having a low battery issue. Found the alternator was putting out 14.2 volts but voltage out of isolator is only 13.4 volts.
It is a Sure Power model 3002 isolator.
300 amps.
Don’t really want to go to mothership $$$$$
Coach 1267, 2009 front entry
Not sure if this would work for you, here is a P/N 3003
Steve & Doris Denton
45' Newell #525, Bath & Half
2014 Honda CRV Toad
I have a SurePower 2402, 240 amps, that you can have for the shipping. I took it out of my coach when I put the Lithiums in.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )
Forgive my ignorance, but I am confused...and I admit that I have not measured the input and output of my isolator...but....

My silver leaf regularly reports that my voltage with engine running is 13.8V.  You are measuring 13.4V.  It seems to me that a half a volt is not gonna cause battery problems.

If you are interested, can you say more about what you are seeing?   Could batteries be failing?  If they are original then they are approaching their end of life.  Do you have a trickle charger?  (I had a trickle charger that was not working and had tons of battery problems until I fixed it — there is a thread about that here.

I am not saying the isolator is not bad...but for it to be a problem I would be thinking more about current that voltage.  

Bill Johnson
2003 Newell #653 Quad Slide Cat C-12 engine with Motorcycle lift 
2011 Jeep Wrangler, 2018 BMW 1200GS Adventure Motorcycle
Auburn, Alabama
The correct charging voltage for wet cell batteries is between 13.7 and 14.7 volts. Most automotive systems produce 14.2 volts which is considered standard.
My alternator is producing 14.2 volts but I am losing .8 volts at the isolator so voltage going to the battery is 13.4 volts.
Due to inherent charging losses you need a minimum of 13.7 charging volts to obtain a full charge.
I know 1/2 a volt doesn’t seem like much but it actually is.
The batteries are brand new,
I replaced them because the old batteries were old and seemed weak.
Most likely the old batteries were actually still ok, just undercharged.
When the new batteries wouldn’t start the coach I started looking at the charging system.
That’s when I found the problem!

I’ve learned a lot about battery charging in the last couple of months.
Coach 1267, 2009 front entry
One last thought.   The Cole-Hersey merge relay is a known source of issues.  I believe that it is wired in parallel with the two outputs of the isolator.   Have you removed it as a source of the voltage drop.  The reason that I mention this is because it would be way cheaper to replace.

Also...If you are contemplating ever upgrading to Lithium may want to look into an isolator that has a high amperage rating.   My alternator can put out close to 300 amps and the batteries can take all that and more....but the isolator is rated for far less current than that.   So, if the lithiums are run down and the engine is cranked, you could easily overload the isolator. Just a thought.

I found these guys who make solid state isolators, but did not buy one yet.  Perfect Switch

Bill Johnson
2003 Newell #653 Quad Slide Cat C-12 engine with Motorcycle lift 
2011 Jeep Wrangler, 2018 BMW 1200GS Adventure Motorcycle
Auburn, Alabama
Just for grins, have your disconnected the lithiums from the isolator and did that impact the voltage? I only ask because my isolator and the replacement isolator did not function properly once the lithiums were installed. I do not know why.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )
Yes the Hersey relay is wired in parallel and connects both banks.
And your thought about the lithium battery is correct in that they can accept much more charge.
In fact that may be what caused the failure of my isolator.
I installed 3 200ah lithium’s about 4 months ago.
“They are drop in replacements say’s the battery salesman”
Well, if you read the fine print in the lithium charging instructions, at the bottom of the page (of course, wouldn’t want to make it obvious). You will find warnings about charging with an alternator!
In conversing with Richard who has also went the lithium route. He tells me that he has disconnected his lithium’s from the isolator. And depends on the inverter for charge of the lithium’s.
I’m not sure of my alternator size, I think it is 300 amp that seems to be pretty common in the Newell’s. The isolator I have is 300 amp that I know.
So in summary, if you want the ability to charge from the alternator. You need not only a large isolator, you also need a regulator capable of regulating both voltage and current to protect your alternator.
Richard tells me he has researched this and that type of regulator is expensive.
So I think I will follow Richards path to a solution.

I have not disconnected the lithium’s. I will check that out, and let you know my experience.
Coach 1267, 2009 front entry
Dear Gurus,

Battery isolators are just large diodes which function as one-way check valves for electricity. A good meter will indicate 0.72 v drop across a diode. That is just normal.

Lead acid batteries normally "like" around 13.7 volts when it is hot outside and up to 14.2 volts when it is cold weather. If you have 13.7 (with an accurate meter),
the batteries should charge and stay charged.

However, I'm not for sure which Newells have isolators. For example in out 1991 #277, Newell and the book states I should leave the battery bus tie relay on all the time.

It appears to me another good source of isolators AND big alternators is HD Power Solutions (817 535-0284, 5083 Martin Luther King FWY, Ft Worth, TX 76119, On our coach, I really needed the power output opposite of where it normally is and they changed it around for me. If you contact them and tell them your needs before they build and ship your unit, it is a no charge request.

Happy RVing!
Also, I have noticed that Battleborn is selling a specific isolator for Lithium batteries with an automatic 15 mins on, 20 mins off to protect the alternator.
Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )

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