Battery Isolator

WebDog · 04-09-2005, 11:24 AM

Hey i got a question, Lets say my alternator is 120A would i need to get a 120A isolator? or would a 80A work fine?

n8scstm · 04-09-2005, 11:28 AM

You would need to go with at least a 120 amp isolator. THe one I have is a sure power. Make sure you get one to fit your alternator. Some require external excitation which means you'll have to hook up a wire from an acc. source to the isolator then to the alternator, or else the alternator will never turn on. Napa auto parts sells them, but they repackage them and put their name on it. I think you will need a 12023a, which is the same one that I have. http://www.surepower.com/pdf/isolatorguide.pdf
http://www.napaonline.com/cgi-bin/nc...2&prmenbr=5806 If you need alternator adapdater wires you can buy them here. http://www.nwreg.com I got a cool in line harness that includes a 3 foot sense wire that plugged right into the isolator so I didnt have to do any cutting or splicing.

WebDog · 04-09-2005, 12:00 PM

ok cool. I knew you could awnser that...

Im goign to the welder today to have my mount welded so i can bolt it up. What amperage fuse would you use on the wire? i have a 150A and a 300A what one would be better?

n8scstm · 04-11-2005, 11:00 AM

I'm only using an 80 amp circuit breaker ( http://froogle.google.com/froogle?q=...7114&scoring=p )on the line from the alternator. I'm not sure why, but that's what the isolator recomended in the instructions. It seems weird since the alternator is capable of putting out 120 amps. I then uses a 300 amp wafer fuse on the line going from the aux battery to the fused junction block. I got the fuses from http://www.patsexpress.com

Qty PartNumber Product Price ExtPrice
2 071-958 300A GOLD PLATED WAFER FUSE $3.90 $7.80
1 263-630 WAFER FUSE HOLDER $5.80 $5.80
1 263-720 PHOENIX GOLD G100 FIREWALL GROMME $4.95 $4.95
1 CATALOG FREE CATALOG $0.00 $0.00
1 263-134 TSUNAMI FDB1004-MANL 4 POSITION F $47.55 $47.55
1 263-142 TSUNAMI FS-MANL150-5 MINI ANL FUS $7.50 $7.50
1 UPS-GroundTrac $8.83 $8.83

TOTAL: $82.43

There are all the part numbers.

wizawuza · 04-11-2005, 11:07 AM

Quote: Originally Posted by n8scstm

I'm only using an 80 amp circuit breaker ( http://froogle.google.com/froogle?q=...7114&scoring=p )on the line from the alternator. I'm not sure why, but that's what the isolator recomended in the instructions. It seems weird since the alternator is capable of putting out 120 amps. I then uses a 300 amp wafer fuse on the line going from the aux battery to the fused junction block. I got the fuses from http://www.patsexpress.com

I'd guess that this is because, while a spike in current above 80 amps may not blow a fuse, a spike in current above 120 amps will kill the relay.

For instance, if you got a 120 amp fuse.. for a VERY brief moment, you got 140 amps, your fuse may not blow, but your relay is going to die... just a guess

WebDog · 04-11-2005, 01:40 PM

Ok thanks,
For now i just connected both batterys together, fused at each battery. if i have problems with low power ill do a isolator or relay. I kind of like the idea of being able to flip a switch and start the car lol.

but for now im doing it this way and i dont have to rewire everything yet.

n8scstm · 04-11-2005, 08:13 PM

But you will still have to worry about not being able to start your car. Which battery did you go with?

WebDog · 04-11-2005, 08:23 PM

I went with red top under the hood and moved the yellow under the rear.

Ill see if i have problems with them being one. If i do i may add a high amperage relay between the two.

WhiteRabbit · 04-12-2005, 11:15 AM

remember, at full on, your alternator is still shared between at least two batteries. With a 120 amp alternator, you will need at least a 60 amp isolator.

with a 120 amp isolator, you will be good to go up to a 240 amp alternator with two batteries, assuming they are identical.

from a purely physics standpoint, your isolated battery might have a far lower ESR than your starting battery. even so, it would have to be half your starting battery to require that 80 amp isolator......

to put it back in a real world application, your two batteries are now shared on the alternator, along with your motor, your AC, fuel pump, etc etc etc.....

an 80 amp isolator will be enough for a HO alternator and two batteries, if you wanted.

WhiteRabbit · 04-12-2005, 11:17 AM

Quote: Originally Posted by WebDog

Ok thanks,
For now i just connected both batterys together, fused at each battery. if i have problems with low power ill do a isolator or relay. I kind of like the idea of being able to flip a switch and start the car lol.

but for now im doing it this way and i dont have to rewire everything yet.

I actually like this idea. I wish I would be happy with having a simple setup like this, but its fantastic from a performance perspective. as long as that switch isnt flipped, we would never kill our ability to start the car! But once we want to eliminate that switch from the scene, it becomes really really tricky, doesnt it?

WebDog · 04-12-2005, 12:29 PM

Well the idea is with those relays is to have a 3 way switch so one way is always charge both when acc is on, then their is a off, and then their is a always on.

So it would work just like a isolator, if i found a way to make the relay swtch only when engine is on.

Right now with out any "protection" i just have a double capacity battery, so i should be able to run the audio same amount of time as before and not have a problem since before it would still start, barely.

WhiteRabbit · 04-12-2005, 06:54 PM

I dont really understand the way you have your three way switch wired up.

But I definitely understand the desire to want to have a good system of isolating the rear without using diodes allowing me to run the secondary battery dry but not the main. did your wiring scheme solve that problem? and if so, could you re explain it? I didnt quite get it.

WebDog · 04-12-2005, 08:22 PM

Heres what im thinking:

Switch position 1:
Relay closed when engine on. Both batterys connected only when engine is on. Not via acc.

Switch position 2:
relay open all the time. Both batterys never connected.

Switch position 3:
Relay closed all the time. Both batterys connected all the time.

n8scstm · 04-13-2005, 12:27 AM

The only problem with using relays rather than diodes is that if you have a dead aux battery and try to start your car, when you turn the key and start cranking the relay will close. Then you'll be trying to recharge a dead battery and start your car at the same time. This may not always work. Also, there maybe be a voltage drop cased by the starter on the aux battery. Maybe you could make a circuit that would close the relay after a few seconds of the engine running. Not instantaneously.

WhiteRabbit · 04-13-2005, 02:11 AM

n8, youve touched on subject #2 that I've always found very, very bothersome, and have never found a good solution for.

the timer isnt too bad an idea. complicated, but not a bad one. do you think its possible to achieve the same performance with a simpler technique?

webdog, I actually ran a more primitive form of your solution for awhile. Id be willing to bet that there are dozens of members on this board who do the same, run a switch. I got tired of it, personally. its ugly, its extra work, switch positions have to be memorized, the switch can't be forgotten upon vehicle exit or else bad things may happen, etc etc etc. the attention to detail just isn't there!

so that leaves us with the goal of designing basically a diode isolator without the voltage drop. not an easy task! the switch is simple, easy, and it works. but is not elegant.

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