Wiring Relays in Parallel Please READ

[shizzzon 461]

I am (hopefully) about to order an upgraded alt for my car soon. I have 2 200A solenoids in the car and I need to make sure they are wired correctly before i take a chance in the alternator burning them up.

EVERY COMPANY i have talked to has told me to wire them the same way but i do not believe them as it doesn't sound right so i want your guys opinion.

Here is a pic of them-

The top option- this is the way the companies want me to wire them, main wire from batt coming in, running of relay one to input of relay 2 then out of it to battery bank... Wouldnt that just switch 200A into another relay to only support 200A of current???

Option 2, the bottom one is what i am thinking-

Main wire from batt comes in to input of relay 1 and 2. Output from relay 1 and 2 are ran together then ran to battery bank.

[BKOLFO4 29]

With the top pic, you might as well just have one relay, since the same current will pass through both.

With the second option, the relays are in parallel and the current will be divided between them.

[shizzzon 461]

thats what i figured...

Well, gotta rewire em before that alt gets put in there... i hate it when people lie to me.

[helotaxi 46]

I'm gonna guess that they told you correctly and either did a poor job of explaining it or you misunderstood what they were saying.

[shizzzon 461]

i told them that i wanted to wire them in parallel because i had mroe than 200A of current being flown threw there soon. They all told me the same thing-

When the wire from front batt comes in, just run it out of the first relay to the input of the second then out of that one to your aux batteries.

So i ask again, just in, out, in, out?

They said yea.

Well, i know the answer now. I thought i was right to begin with, that's why i made this thread before somethin got melted soon, hehe

[lilblacky 0]

excuse my noobishness.... what exactly do they do?

[shizzzon 461]

they isolate the front battery from all the extra batts in the rear. You need this because over time, all the batts being tied together will try to all share the same charge level. If using different battery technologies, the batts will drain each other down til they die if not charged all the time.

Now, when the car is started, all batts are tied together so the alt can keep them all charged.

The isolators are to prevent premature failure of the front or rear battery bank.

[lilblacky 0]

ooooooo got ya.... hmmm how much are they?

[shizzzon 461]

u can get em for like ~$50 per 200A Solenoid. They also are called Relays too. Do NOT get them confused with the term isolator as that has a nasty voltage drop vs Solenoids.

[lilblacky 0]

oh that aint too bad... how many would i need if im runnin 2500wrms? or does the amount you runnin not matter.

Does it matter how many batteries you have?

Edited July 17, 2008 by LilBlacky

[shizzzon 461]

from what i was told... knock on wood, it depends on how much alternator power you have. Since i will have 250, i needed 2 of them in parallel.

It is the purpose of current transferring from front to rear. Since that should only happen from the alt... well u see.

[lilblacky 0]

ahhh that makes sense... maybe ill invest in 2 of these as well because i just bought a 250a alt