Battery isolator between one dead and full battery

[davidh86]

Ok From what i understand, linking one full battery to one discharged batter using a standard batter dial will cause the full battery to discharge a large amount of energy to the dead batter and damage it over time. Now i know an isolator will stop one battery from discharging another battery while the engine is off but does this principle apply when the engine is on or only when it is off and the the alternator isnt giving current to the center terminal? Ive also looked into the voltage sensing relay but im assuming when the engine is on the flow between the two batteries is uninterrupted. Oh and if i were to use the isolators would the separate banks still get their own charging leads from my 120v battery charger?

Thanks,
David

 

[fhhuber]

Put the low battery on a charger..... Then once charged connect it.
Just from an abundance of paranoia. its better to avoid creating a potential for a big spark while hooking things up.

The isolator is generally expected to allow the engine charging system to charge both batteries but not allow either battery to supply the other.

and you'd need a charger built to deal with isolated batteries... if you connect 2 isolated batteries to a single standard charger then you'd defeat the isolation system.

 

[alldodge]

Ok From what i understand, linking one full battery to one discharged batter using a standard batter dial will cause the full battery to discharge a large amount of energy to the dead batter and damage it over time. Now i know an isolator will stop one battery from discharging another battery while the engine is off but does this principle apply when the engine is on or only when it is off and the the alternator isnt giving current to the center terminal?

Yes, when motor is running or off the isolator keeps ne battery from discharging into the other.

Ive also looked into the voltage sensing relay but im assuming when the engine is on the flow between the two batteries is uninterrupted. Oh and if i were to use the isolators would the separate banks still get their own charging leads from my 120v battery charger?[/QUOTE]

Yes and No, only if the one charger positive is connected to the main input from the alternator output connection, that's the yes. The No, that said, charger output can supply the power but the since will not be sensed by the charger (wrong side of the diode).

 

[davidh86]

No Title

I planned on using a 2 bank 120 charger to power the banks on each side of the isolator. My only concern is if the isolator will work while the alternator is putting power though it and stop the dead battery from receiving a massive jolt of power from the full one. ive had allot of issues burning up new sets batteries using an old dial switch which linked up the batteries in parallel and caused damage to the battery that was dead. I attached a picture to show what im trying to do.

Thanks,
David.

 

[bruceb58]

If you start your engine, your alternator is going to put all of its current to the empty one until it's voltage rises up to the voltage of the full one and then you will start having some current flow to the full one.

If you use a diode isolator, there will never be a chance of the full battery sending current back through the isolator diode. That is why it is designed with a diode.

Just so you know, it's really bad to try to charge a completely dead battery with an alternator. Way better to use a battery charger to bring it up first.

Use the 2 bank charger method. Don't have a charger charge across a diode isolator. It won't fully charge the battery because of the diode voltage drop.

 

[bruceb58]

Personally, I use an ACR. It is way better than an isolator. If you have a completely dead battery, It will not even let the dead battery get connected thus saving your alternator. It does a voltage check and makes sure nothing less than a battery with a partial charge get connected.

 

[davidh86]

Personally, I use an ACR. It is way better than an isolator. If you have a completely dead battery, It will not even let the dead battery get connected thus saving your alternator. It does a voltage check and makes sure nothing less than a battery with a partial charge get connected.

would an acr stop the flow from the full battery from damaging the partially drained battery? Oh and am i blowing the whole full battery damaging a discharged battery concept out of proportion, is their more to it? Sorry for all the question just dont wanna spend a fortune in batteries again lol.

 

[bruceb58]

The ACR won't connect until the voltage is up to 13.5V and will disconnect if both sides get below that number so they will basically only be connected while the alternator is outputting.

I would be way more worried about the scenario of a damaged shorted cell battery drawing all your current from an alternator through the isolator. and you not knowing it.

 

[alldodge]

Alt is outputting, and ACR is connected, and if battery has shorted cell then all the output is going to the shorted bat.

Alt is outputting, and isolator is connected, and if battery has shorted cell then all the output less .7V is going to the shorted bat.

 

[bruceb58]

Alt is outputting, and ACR is connected, and if battery has shorted cell then all the output is going to the shorted bat.

Only if the battery has a voltage over 10.0V. If not, it will never connect. This assumes a BlueSea ACR.

 

[alldodge]

Only if the battery has a voltage over 10.0V. If not, it will never connect. This assumes a BlueSea ACR.

Looks to be if it drops below 12.75V now

An ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR??s contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A/FAQ

 

[bruceb58]

Yes, if the ACR is currently connected and then the voltage drops to 12.75V, it will disconnect at that point. If the voltage starts out below 9.5V(one of their specs said 10.0V elsewhere), it will never connect in the first place.

 

[davidh86]

Ok awesome i'm gonna go with the blue seas system thanks for all the input guys.