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Dual battery setup question - starting from aux battery...

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william_7900

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I have a question concerning setting up dual batteries on my 71 Blazer.

I installed a 2nd battery tray and a second Optima battery.

I installed a 200 Amp continuos voltage solenoid. I connected the new battery (positive post, negative is grounded to the engine) to one of the large posts on the solenoid. To the other large post on the solenoid I connected to the large post on the starter (which is connected to the positive post of the primary battery.)

When energizing the solenoid, the batteries should be connected in parallel.

Here is my question. If i disconnect the positive post of the primary battery, shouldn't I be able to start my Blazer by energizing the solenoid which is connecting the aux battery to the starter?

Instead the starter will only click (once) as if the battery is almost dead. Even if i connect the primary battery through the new solenoid i still only get the click when i turn the key. I can hear the solenoid engage when I turn the key to on (not past to start) so it know it is working.

Should I be able to start through the solenoid?

Any ideas?

Thanks for any help.

William
 
william_7900 said:
I have a question concerning setting up dual batteries on my 71 Blazer.

I installed a 2nd battery tray and a second Optima battery.

I installed a 200 Amp continuos voltage solenoid. I connected the new battery (positive post, negative is grounded to the engine) to one of the large posts on the solenoid. To the other large post on the solenoid I connected to the large post on the starter (which is connected to the positive post of the primary battery.)

When energizing the solenoid, the batteries should be connected in parallel.

Here is my question. If i disconnect the positive post of the primary battery, shouldn't I be able to start my Blazer by energizing the solenoid which is connecting the aux battery to the starter?

Instead the starter will only click (once) as if the battery is almost dead. Even if i connect the primary battery through the new solenoid i still only get the click when i turn the key. I can hear the solenoid engage when I turn the key to on (not past to start) so it know it is working.

Should I be able to start through the solenoid?

Any ideas?

Thanks for any help.

William
Click to expand...

draw up a quickie diagram of what you did and I'll tell you exactly whats wrong....
 
After thinking about it for a little while it should work as long as you retain enough voltage at the small terminal to keep the continuos duty solenoid activated.
 
added diagram (see attachment)

Here is how i have it wired (see attachment). Again, the starter won't turn (only clicks once) when i disconnect the primary and try to start, even though the secondary is directly wired to the starter through the solenoid.

thanks for any help.

William

battery isolation diagram.jpg
 
From that drawing it should be impossible to energize the solenoid since there is no voltage at the starter until the solenoid is energized. If you were to wire in a switch from the AUX battery to energize the solenoid then it should work.

Also, you would need to make sure the solenoid is grounded to the engine block and not just the chassis since there is rubber motor mounts. Basically your primary batterys negative cable has a small pigtail that is grounded to the chassis and would make a good ground but since you probably don't have a cable with the same small pigtail grouded on the chassis with your AUX battery that is why it would need to be grounded on the engine as well.
 
what he said...

there's no way to energize the solenoid if your primary is disconnected... a simple paralleling switch will take care of that, powered off the #2...

and yeah, watch your grounds there... real easy to nuke stuff out when it doesn't have a proper sized grd.. most parallel systems grd the batteries together, then to eng... but redundancy never hurts on a grd system..

keep in mind too, you will not be charging that #2 battery with it wired that way, only when the solenoid is closed...
 
I would wire it up just like it's supposed to be, then if you want to be able to use the AUX battery for starting in case your primary goes dead then wire in a second switch from the AUX battery to activate the solenoid. If your primary battery goes dead and you use the AUX battery for this purpose you will shorten the life of both batteries. Read the link i posted back on my first reply and you'll understand why.
 
4X4HIGH said:
I would wire it up just like it's supposed to be, then if you want to be able to use the AUX battery for starting in case your primary goes dead then wire in a second switch from the AUX battery to activate the solenoid. If your primary battery goes dead and you use the AUX battery for this purpose you will shorten the life of both batteries. Read the link i posted back on my first reply and you'll understand why.
Click to expand...
When you say "just like it is supposed to be", I am no longer sure how it is supposed to be... I'm guessing from your post above that i should not be using a solenoid at all...

Is there no way to use a solenoid without potentially damaging my system?

Williajm
 
Get rid of the wire that runs from your battery to the starter run it to the solenoid also or to another one.

Run the wire that goes to the starter from the alternator to the solenoid so it will charge both batteries, or to a isolator so that it can properly do both.

On the starter there is a big post and a little one connect those two together so that when the big one gets power the starter works.

I have used remote starter solenoids in all my rebuilt vehicles and they work fine. My Burb has two.

You can set them up so that either battery will start the truck or both at the same time and keep one for only starting and one for other stuff or just about any other way.

The wire that runs to your starter should only be hot when you are trying to start it.
 
The way that I have it set up is all my power for my truck comes off of the positive side of the solenoid the only wire that goes to my starter is the wire from the solenoid that is hot when the solenoid is tripped.

Hope that clarifies my mixed up post
 
I figured out what most of you probably already knew... the large post on the alternator is connected directly to the primary battery which is how it gets charged. Not sure where to connect it to have it charge both the primary and the secondary... thoughts?

I also figured out that there is a difference between connecting to the ignition circuit on your fuse box and connecting to some other fuse box connection (such as for the radio) when trying to energize a solenoid to start the vehicle - i would really like to know the difference though.... any thoughts on this?

William
 
Last edited:
new diagram...

Would this work (see image)? Would it be bad to connect the alternator directly to the 2nd battery as it is already directly connected to the primary battery?

The switch would normally stay on but it would allow me to disconnect the secondary battery from the system if desired.

Thoughts?

battery isolation diagram.jpg
 
Try this -

9112.jpg


I know it's for a boat, but the idea is exactly the same.

Later,
Buddy
 
haha, I see the ACR stuff is finally taking hold around here.... :D

William, the problem your going to have is, any effort you make without an isolator or my preference, an ACR setup, to charge both batteries, will in effect put them in parallel... backfeeding thru that alt connection.. thus defeating the "aux battery, always charged for emergency" thought..

As everyone knows, there are MANY ways to do dual bats, from straight out parallel, to much more complex systems...

Isolator tech such as the hellroaring kits, etc have been quite popular and effective for years.. Tho any isolator system does, and can have drawbacks... voltage loss, no start failure conditions, etc...

not that the 9112 ACR's are without potential probs, but imo, it's a far better system...

marine bat switches are another avenue to throw in the mix. my system combines a marine switch and ACR.. the most flexible, bulletproof setup I could come up with...
 
kgblazerfive said:
pic of mine
Click to expand...
KGBlazerfive, Ryoken,

1st, thanks for the help - i really appreciate it. It is guys like you that make these forums so helpful/valuable.

Is it bad for the batteries to be in parallel while the alternator is charging them?

Also, can i connect the alternator directly to the second battery? Basically without buying an isolator, how can the alternator know that one (or both) of the batteries need to be charged if at all...?

I wanted to get out of purchasing the HellRoaring or Painless solution due the cost. I think most of us here can afford those but coming up with a solution using what you can scrounge together to me is more satisfying... (you may say always having a charged secondary battery is more satisfying... :-) )

Also, i have already learned a bunch trying to put this together which is a great so again thanks for the help.

William
 
Well it will charge them both but it will just charge them both, if one for some reason has a lower voltage it will just charge them both, where a isolator will charge them evenly to their needs. It will work and charge eaither way.
 
It doesn't matter how many batteries you have in a vehicle the alternator will give the most charge to the battery with the least voltage in it. The alternator will not charge more than one battery at the same rate.
 
4X4HIGH said:
It doesn't matter how many batteries you have in a vehicle the alternator will give the most charge to the battery with the least voltage in it. The alternator will not charge more than one battery at the same rate.
Click to expand...
if the alternator will not charge more than one battery at a time, should i connect the alternator directly to each battery? Otherwise it seems the alternator would just see one battery (when connected in parallel).

William
 
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