Anyone use a battery isolator on a dual battery drag car

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Duane

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Just curious if there is anyone doing this or any reason too that I have not thought of.
I was thinking of running just the water pump and rad fan off its own battery while in the pits.
 
You probably should. Either that or have 2 different chargers, one for each battery. My last tool truck didn't have a isolator. It was a battery boiling sob. The interior light batteries always needed a charge but the engine start batteries didn't. Guess which ones got boiled dry often. Yep the engine start batteries.
 
I don't run isolators on race cars, for two reasons. First, a battery isolator is basically just a set of high current diodes. And a characteristic of a diode is that when the diode is forward biased, (conducting) there will be drop in output voltage compared to the input voltage, of around half a volt. This means that the battery will never see the full voltage being supplied from the battery charger, and for some of the new battery chemistries, that's a problem in itself. Secondly, in my experience they are somewhat unreliable and have a habit of failing at the worst possible time.
For drag racing, I also like to run the fans and water pump between rounds. So what I do, is use an Andersen connector on the connection to the fans and pump. I can connect it to the cars electrical system or in the pits I can connect it to an external DC power supply that is powered by the generator in my trailer. That way, I can run the cooling system as long as I want, and never run down the batteries in the car.
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Garry in AZ said:
I don't run isolators on race cars, for two reasons. First, a battery isolator is basically just a set of high current diodes. And a characteristic of a diode is that when the diode is forward biased, (conducting) there will be drop in output voltage compared to the input voltage, of around half a volt. This means that the battery will never see the full voltage being supplied from the battery charger, and for some of the new battery chemistries, that's a problem in itself. Secondly, in my experience they are somewhat unreliable and have a habit of failing at the worst possible time.
For drag racing, I also like to run the fans and water pump between rounds. So what I do, is use an Andersen connector on the connection to the fans and pump. I can connect it to the cars electrical system or in the pits I can connect it to an external DC power supply that is powered by the generator in my trailer. That way, I can run the cooling system as long as I want, and never run down the batteries in the car.
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Can you share some more info about your setup. Do you use an alternator to charge both batteries, and what gauge wire from the alternator to the trunk.
The generator you speak of, are you using the dc output from the generator to directly power the water pump and fan.
Are you familiar with the relay type of isolator that has no diodes?
 
I agree with Mike because in this day and age you have many choices for REGULATED chargers/ maintainers which will properly charge and regulate batteries. All isolators have some voltage drop and will not charge the batteries equally, and can not "sense" which or if either battery is low.

Isolators were always a problem for me, as "up here" there were two boat explosions with isolator equipped systems, here is the problem:

In an alternator/ engine situation, the regulator only senses the main battery. The second battery also gets charged, but the regulator "reads" off the main

What can happen is that one of the two diodes in the isolator can open, and now the regulator says "hey, the main batt is going dead, let's charge to beat hell." And so the voltage regulator ramps up, and is charging the pee waddin' out of the SECONDARY battery.

I'm not sure one charger would do any different.
 
67Dart273 said:
I agree with Mike because in this day and age you have many choices for REGULATED chargers/ maintainers which will properly charge and regulate batteries. All isolators have some voltage drop and will not charge the batteries equally, and can not "sense" which or if either battery is low.

Isolators were always a problem for me, as "up here" there were two boat explosions with isolator equipped systems, here is the problem:

In an alternator/ engine situation, the regulator only senses the main battery. The second battery also gets charged, but the regulator "reads" off the main

What can happen is that one of the two diodes in the isolator can open, and now the regulator says "hey, the main batt is going dead, let's charge to beat hell." And so the voltage regulator ramps up, and is charging the pee waddin' out of the SECONDARY battery.

I'm not sure one charger would do any different.
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I was reading that a relay type isolator does not suffer from these diode problems. These type simply disconnect the isolated starting battery. When the engine is started, a 12 volt ignition trigger wire
Rejoins the two batteries together to function as a normal two battery parallel system. Any thoughts on this?
 
On my drag car I only have one battery. I have a 95 amp alternator, and a wide open throttle micro switch on the carb, that opens the alt field circuit at WOT. Any other time the charging system works normally. Also have a time delay relay on the fan/water pump system, that turns them off after a preset (adjustable) time, so I don't kill the battery, if I get running my mouth and forget to turn them off.
 
Duane said:
I was reading that a relay type isolator does not suffer from these diode problems. These type simply disconnect the isolated starting battery. When the engine is started, a 12 volt ignition trigger wire
Rejoins the two batteries together to function as a normal two battery parallel system. Any thoughts on this?
Click to expand...

That is what I always used to use, another word is "continuous duty solenoid." Looks something like a Ford/AMC fender mount solenoid, but designed to be "on" continuous. Another thing you could do if you are just manually charging it, is just use a disconnect switch to jumper them together.

The really best way is to use two chargers. That way neither battery will try and pull the other and the chargers can properly sense voltage Whichever battery is your starter battery will undoubtedly be "down" in relation to the other through a race weekend
 
67Dart273 said:
That is what I always used to use, another word is "continuous duty solenoid." Looks something like a Ford/AMC fender mount solenoid, but designed to be "on" continuous. Another thing you could do if you are just manually charging it, is just use a disconnect switch to jumper them together.

The really best way is to use two chargers. That way neither battery will try and pull the other and the chargers can properly sense voltage Whichever battery is your starter battery will undoubtedly be "down" in relation to the other through a race weekend
Click to expand...

My tool truck had a constant duty relay but it still overcharges the one set of batteries. Separate chargers is the best bet.
 
67Dart273 said:
That is what I always used to use, another word is "continuous duty solenoid." Looks something like a Ford/AMC fender mount solenoid, but designed to be "on" continuous. Another thing you could do if you are just manually charging it, is just use a disconnect switch to jumper them together.

The really best way is to use two chargers. That way neither battery will try and pull the other and the chargers can properly sense voltage Whichever battery is your starter battery will undoubtedly be "down" in relation to the other through a race weekend
Click to expand...
Ok I hear you on the two chargers and the relay type isolator.
Do you still allow the starter to crank off both batteries when starting the engine. Would this be the only time the batteries are connected. Could you post a drawing showing how you are wired.
 
Dual batteries must be identical.
I have seen isolators burn up on more than one occasion.
Solenoid type is just that as mentioned above. Or just go old school and use a manual dual battery switch. On any multi battery system, a bad battery will ruin the good one by forcing alt to overcharge.
 
Duane said:
Can you share some more info about your setup. Do you use an alternator to charge both batteries, and what gauge wire from the alternator to the trunk.
The generator you speak of, are you using the dc output from the generator to directly power the water pump and fan.
Are you familiar with the relay type of isolator that has no diodes?
Click to expand...

Duane, Yes the cars alternator charges both batteries. The batteries are wired in parallel all the time. The charge wire from the alternator to the starter terminal is 4 gauge stranded copper. The output of the alternator is rated at 80A. The batteries are connected to the starter terminal with 1/0 gauge stranded copper cable.

No, the generator I have does not have a DC output. It powers an Elgar 120V AC to DC convertor. The output of the Elgar convertor gets connected to the cooling plug.

The solenoid type isolation has it's own issues, some of which are mentioned above. I prefer to never isolate the batteries from each other.
Another way to solve your problem is to simply use a battery charger that will keep the batteries charged while the cars pump and fans are running. Just make sure it's a self regulating charger that decreases it's output when the current load is removed, or you'll overcharge your batteries.
 
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