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Old 01-07-2020, 09:52 PM   #1
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Battery isolators

I would like to get some opinions on battery isolators. Diode or solenoid? And why. Thanks in advance for your time.


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Old 01-08-2020, 12:49 AM   #2
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During our build, we used a Stinger solenoid to isolate our house bats from our bus bat so we could use the alternator to charge the house bats while driving. Simple switch to activate the solenoid. So glad we went that way, the Stinger went bad and we were in the middle of nowhere to get a new one. However, any old auto parts store has a " continuous duty solenoid" was a perfect fix, running it ever sense.
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Old 01-08-2020, 01:15 AM   #3
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Quote:
Originally Posted by russsh View Post
During our build, we used a Stinger solenoid to isolate our house bats from our bus bat so we could use the alternator to charge the house bats while driving. Simple switch to activate the solenoid. So glad we went that way, the Stinger went bad and we were in the middle of nowhere to get a new one. However, any old auto parts store has a " continuous duty solenoid" was a perfect fix, running it ever sense.
Hey thanks for the info Russsh. Do you know what your solenoid amps is rated for? What is your house battery bank in amps?
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Old 01-08-2020, 10:03 AM   #4
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Neither is my reco.

Unless your House bank is **only** getting charged by an alternator which is wired directly to the Start batt.

Which IMO is sub-optimal.

But if that is the case then $50 solenoid will indeed do the job.

Diode based isolators usually add too much voltage drop.
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Old 01-08-2020, 10:11 AM   #5
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So if I use a relay isolator, and drain down my deep-cycle AGM batts, when I run the motor and alternator, will the deep cycle batts pull amps from the starter batts?


The diode isolator website I looked at (trying to figure out what the hell that thing under my bus exactly was) says it will allow the charge from the alternator to go to the weak battery, without overcharging the full battery. I could also get one that isolates several batteries from each-other this way. That last option looks nice, since I will have 2 starter batts, and 2 AGM deep cycles.



Any comments on that?
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Old 01-08-2020, 11:06 PM   #6
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I believe the amp rating for the solenoid is 200 continuous. We have 4 6v golf cart house batteries, wired up for 12v. I have a switch to activate the solenoid manually so i can isolate the house and starter bats at will. Have a 5.9 Cummins which i think has a 160amp alternator, when house bats are down abit, i flick the switch while driving, the bus amp meter jumps to about 90 amps, and slowly goes down as the bats charge. Cool thing, if my starting bats gets low, i can jump it with a flick of the solenoid switch.

4 6v bats, 230ah, wired 2 in series to give me up to 12v bank, then in parallel to give me more ah time. 460 total ah, at 50% usable, 230 usable amps
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Old 01-08-2020, 11:09 PM   #7
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BTW, we have an RV shore power 4 stage 90amp charger/conditioner for the house bats too. When plugged in, we can charge and maintain both house and starter batteries with that. 3 years full timing, seems to work. Solar is next on the never ending list!
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Old 01-08-2020, 11:10 PM   #8
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The whole point is connect when charging is happening, so current flows to House from the alternator not the Start batt.

Two batteries makes a single bank, treat as one unit.
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Old 01-09-2020, 08:18 AM   #9
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Quote:
Originally Posted by russsh View Post
I believe the amp rating for the solenoid is 200 continuous. We have 4 6v golf cart house batteries, wired up for 12v. I have a switch to activate the solenoid manually so i can isolate the house and starter bats at will. Have a 5.9 Cummins which i think has a 160amp alternator, when house bats are down abit, i flick the switch while driving, the bus amp meter jumps to about 90 amps, and slowly goes down as the bats charge. Cool thing, if my starting bats gets low, i can jump it with a flick of the solenoid switch.

4 6v bats, 230ah, wired 2 in series to give me up to 12v bank, then in parallel to give me more ah time. 460 total ah, at 50% usable, 230 usable amps
What is the purpose for the switch to isolate at will? Is that so you can jump the start battery at will? I thought that the alternator from the bus charged both battery banks at the same time while driving and isolated them when plugged in on shore power? I hope I don’t sound like a freakin idiot ? Just a bit confused getting all my parts together.

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Old 01-09-2020, 09:15 AM   #10
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They also make a MOSFET battery isolators. They have minimal voltage drop.

I have seen folks have good success with the unit from Victron.

They allow charging both batteries from your alternator but will not allow one battery to discharge the other.

I have seen folks with the solenoid solution and accidentally leave it turned on while camping. They ran their house batteries low and went to start the engine to recharge. Guess what? They inadvertently discharged their starting batteries also.

Regardless of which solution you choose some sort of safety should be in place to eliminate the possibility of accidentally discharging your starting batteries.
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Old 01-09-2020, 11:00 AM   #11
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Quote:
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What is the purpose for the switch to isolate at will? Is that so you can jump the start battery at will? I thought that the alternator from the bus charged both battery banks at the same time while driving and isolated them when plugged in on shore power? I hope I don稚 sound like a freakin idiot ? Just a bit confused getting all my parts together.

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Couple of things, when building our bus, looking at bat isolators, wasn't impressed with the auto diode things, cost and not a fan of exotic hard to get on the road parts.....just my opinion. So we went with the solenoid route.

Over time, I have found that its a nice thing to connect both batteries, and to isolate them too at different times, I have the power to choose what happens to my batteries, i like that. HOWEVER! Someone just mentioned, if your not charging from shore power or solar, dont forget to isolate them batteries, dont want a dead starting bat!
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Old 01-09-2020, 03:51 PM   #12
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Yes the Victron FET based isolators are good but not cheap.

Any choice should be fully automatic in normal operation, nothing to have to remember. Solenoid switched from IGN voltage for example, if alt is the only charge source, or Starter needs no solar.

Manual override, like jumpstarting engine off House if Starter fails, fine but that's for rare events.
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Old 01-09-2020, 05:44 PM   #13
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switches, solenoids, and dead starting batteries

I have a book on my bus, the front few pages are check lists.... check tires, lights, walk around, yadda yadda yadda. part of the road trip check list says interconnect house batteries to alternator. Later this will be changed to .. connect mppt charge contoller to alternator. when the bus gets parked the check list says disconnect house batteries.....

check lists work -- only if you actually follow them. helps keeps airplanes in the air. most of those crashes happen because the check list was not consulted and followed.

want to avoid dead batteries..... start with a check list. confirm situation every time.

wonder how many ever the air pressure in the spare tire? when was the last time you put a pressure gage on the bus tires? check coolant? motor oil? rear differential oil level? brake inspection? inspect belts and hoses?

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Old 01-10-2020, 07:12 AM   #14
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It seems to me everyone has a good argument the way THEY do things on their bus that works for them. I really appreciate all of the input. A lot of food for thought. I have been out of touch with my bus for the last year, but I知 full steam ahead now. I知 determined to have BLUTO complete by the summer. Thanks everyone !!!


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Old 01-26-2020, 12:19 AM   #15
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On the GM PD4106 I知 trying a Magnum Smart Battery Combiner to keep the Start batteries charged from the House batteries via alternator power, shore power, or solar power. Just got the new cables run today. Will be testing it out shortly.
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Old 01-26-2020, 12:44 AM   #16
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Originally Posted by Doktari View Post
On the GM PD4106 I知 trying a Magnum Smart Battery Combiner to keep the Start batteries charged from the House batteries via alternator power, shore power, or solar power. Just got the new cables run today. Will be testing it out shortly.
Post how it works out. If you can, give us a drawing of how you have it set up.
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Old 01-26-2020, 07:36 AM   #17
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will the device current limit to 25 amps? or if you end up with a dead house battery will it potentially over-load the device as a dead bank will likely want to pull more than 25 amps at alternator voltage..

-Christopher
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Old 01-26-2020, 11:46 AM   #18
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Which device are you asking about?

Note that most concerns about inrush over-current are baseless wrt lead banks.

A unit rated for continuous say 60A may be just fine with 400A for a brief time.

Lead batts have such high resistance they're basically self-limiting, any inrush surge does not last long.

Yandina combiners handle the issue very well (and cheaply) just by closely spec'ing the connection wires. She invented the product category (VSR / ACR) gives great support and a lifetime warranty.
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Old 01-26-2020, 12:46 PM   #19
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John the reason I ask is on my regular starter batteries, 2 group 31 12 volt AGM.. (batteries plus top brand whatever it is)... if I run them low... low enough that the engine cranks slow to start but still starts.. (with glowplugs on the dash gauge will read 10.7 or so)... my dashboard ammeter will go close to the peg of 150 amps and run there for awhile before it backs off slowly as the batteries charge up while im driving..



I realize you ardent supposed to run down the batteries that low but reality is that batteries will get run down that low...



thats why I was curious iof those devices limited the current or if they would just fry
-Christopher
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Old 01-26-2020, 01:10 PM   #20
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My Opinion, solenoid uses more energy than diode. The BEST way to protect your start battery is to put a Cut-Off Switch inline between you motor and start batteries. When you 'stop and stay', cut-off the batteries altogether! If you have a solar trickle charger, on the start batteries, you insure that you can 'start n' run' when the mood suits you! Diode isolators are great for sorry free battery charging and use/lose less energy than solenoids and when the batteries top-off they switch over to charging the start batteries only. This provides an opportunity to use more exotic batteries for the RV with things like Lithium and *BMCs to control precise charging profiles. BMC = BATTERY MANAGEMENT CIRCUIT
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