Question aboot voltage @ isolator

[Mcstiggens]

Hi All,

I just hooked up a battery isolator system complete with solar.
My question is, shouldn't the voltage reading on the house battery read the same or similar to the starter battery when the truck is running?
For instance, when I have the truck idling, I get a reading of 14.44v at the truck (starter) battery as well as the input post of the isolator.
But on the output post of iso as well as the house battery I get only 12.75v.
Is that right or should i be getting 14.44v all around?
Sorry if this has been addressed already, I don't have the time to scan the whole thread.

Thanks for the input.

Mcstiggs

 

[jimi breeze]

I would first check the voltage on the auxiliary battery BFORE you start the engine, then compare the voltage after start it. Does it go up? What load is on the aux battery?

 

[Martyn]

Yes get a reading on both batteries when they are at rest, at least 15 minutes after the vehicle has been turned off.

A fully charged battery will read 12.6v -12.65v

With the engine running you are reading the alternator voltage. The difference in voltage between the batteries may be due to the gauge of the cable, the distance of the secondary battery from the alternator, or bad corroded connections.

You may have something within the isolator that is causing the voltage drop. What voltage did you get on the other side of the isolator?

 

[Stumpalump]

It depends on your isolator. The one I use will divert all of the alternator charge to the main battery until it reads 14.7v. Then it will charge the house battery. It's quite a long delay if I need to start the engine to charge the house battery after charging phones and stuff off of the main. Another thing to note is that some isolators use a diode that causes a .6 to.7 volt drop across it. With this type the house battery will never get the full alternator voltage but .7v less.

 

[Mcstiggens]

Thanks for the replies guys. Here are my specs.

With a fully charged battery, the truck turned off, the truck reads 12.79 and the house reads 12.80.
With the truck at idle after 10 minutes, the truck reads 14.78 and the house reads 12.85. So I guess if the isolator
(a 200amp isolator) is meant to only provide a slight trickle, I guess it's working. I just don't know if thats even
enough to call it a 'slight trickle'.

One thing to note, I installed a system using the thread "How to make a cheap isolated dual-battery setup for $50" on this site.
The only difference is that on that schematic, he shows the neg. from the house battery going directly to the truck battery neg.
I just ran the neg from the house down to a good frame location. Seems like 6 one, half a dozen the other to me......or am I missing something?
Also, I used good quality 4ga wire for the iso connections. The only bummer is that i was short of wire by about 4 feet so I had to use an 8ga but connector
(all i could get) to make the connection which kinda negates the use of the 4 ga I guess. Could it have that much effect?

Thanks for the input guys,
Mcstiggs

 

[762X39]

The only difference is that on that schematic, he shows the neg. from the house battery going directly to the truck battery neg.
I just ran the neg from the house down to a good frame location. Seems like 6 one, half a dozen the other to me......or am I missing something?

You likely identified your problem.I don't know why people don't think that the ground isn't important but really, it is half the circuit.If the positive is 10' of #4, then the ground needs to be 10' of #4 right back to the main battery negative.

 

[Mcstiggens]

You likely identified your problem.I don't know why people don't think that the ground is important but really, it is half the circuit.If the positive is 10' of #4, then the ground needs to be 10' of #4 right back to the main battery negative.

Oh sure, I most certainly understand the importance of the negative ground which is why I bothered to grind down to fresh metal in order to (supposedly) achieve it.
It's just, the neg terminal of the truck battery is connected to where? The chassis of course, so therefore I thought any ground wire going to any part of the chassis will achieve ground. It's worked that way my whole life in every other circumstance. I guess this one is special. And I was never aware that the pos/neg wire necessarily had to be the same length.

 

[762X39]

And I was never aware that the pos/neg wire necessarily had to be the same length.

Length isn't important (within reason).

 

[4x4junkie]

I think the main part of your issue is up at the isolator (after all, you did say you're getting 12.75V on the OUTPUT side of the isolator w/engine running, which is indicative it's not putting out any current at all on that side).

Also, your neg battery cable should be connected to your engine block, not the chassis (most chassis grounds I've seen use #10 or so wire). It is possible to use your frame as your ground return, but you do have to make preparations for doing so, one of which is running another cable from your starting battery neg directly to the frame. You'll also want to use copper plates bolted down with 4 or more bolts to spread the current load into the frame around your connection points due to steel not being the greatest current conductor. This will reduce the current concentrating at your (single) connection point, possibly leading to heat issues when current demands are high.

 

[verdesardog]

It sounds like a defective isolator to me.....is it keeping your house battery charged?

 

[Mcstiggens]

I figured it out and it's not a ground issue.

Well, call me a dufus but I figured it out. The problem turned out to be the 12g wire to the fuse box. I had connected it to one of the only two 10 amp fuses with an add'a'fuse, (because the add'a'fuse cautions to only use their product with no more than a 10amp fuse) and it turns out those two 10 amp sockets were for the turn signals. Therefore, they have the flashers involved which well.....I guess thats obvious. So I hooked it up to the neighboring 15 amp and now its working.

Lessons learned, carry on, thanks to you all for chiming in!:ylsmoke:

Mcstiggens

 

[Mcstiggens]

I think the main part of your issue is up at the isolator (after all, you did say you're getting 12.75V on the OUTPUT side of the isolator w/engine running, which is indicative it's not putting out any current at all on that side).

Also, your neg battery cable should be connected to your engine block, not the chassis (most chassis grounds I've seen use #10 or so wire). It is possible to use your frame as your ground return, but you do have to make preparations for doing so, one of which is running another cable from your starting battery neg directly to the frame. You'll also want to use copper plates bolted down with 4 or more bolts to spread the current load into the frame around your connection points due to steel not being the greatest current conductor. This will reduce the current concentrating at your (single) connection point, possibly leading to heat issues when current demands are high.

Thanks, sounds like good advice but for now it works so i just go with it unless things change for me down the line.

Mcstiggs

 

[highdesertranger]

what type of isolator? solid state or solenoid. I find the solenoid type to be much more reliable. to check either one take the main cables off. the big ones that go to both batts. energize the isolator and take an ohm reading across the batt terminals should be zero or close to zero. hope this helps. ok I see now you fixed your problem guess I should have read both pages before I replied. highdesertranger