GMT-800 5.3 battery and dual battery question?

[Martinjmpr]

Still trying to work out solar power for our camping rig but right now the biggest issue is energy storage, i.e. battery.
.
The SuperStart (Deka) that I bought in December is rated at 55ah. It is a Group 34/78 (i.e. it has both side and top terminals - this was a requirement for me as jump starting with side terminals is a total PITA.)
.
Here's my GMT-800 specific question: Is there a 100ah or bigger battery that is in group 34/78? If so, can someone send a link? I have so far been unable to find anything higher than 55ah in a 34/78.
.
As an alternative, how would I set up a dual battery system? What group size would the 2nd battery be? I know there's a space for a 2nd battery under the passenger side of the hood along the right fender, and I believe there is a kit to install, but I'd like to know everything I'd need to install the kit.
.
Thanks in advance!

 

[Martinjmpr]

An isolator isn't necessary though, right? For my relatively limited skill set everything has to be SIMPLE. The simpler the better.
.
For the simplest system, couldn't I just run heavy gauge wire from + terminal on main battery to + terminal on aux battery, and then how does the ground work, does the wire connect the - terminal on the main battery directly to the - terminal on the aux battery? Or does each go to the same ground on the engine? And if so how/where do you connect it?

 

[Burb One]

An isolator isn't necessary though, right? For my relatively limited skill set everything has to be SIMPLE. The simpler the better.
.
For the simplest system, couldn't I just run heavy gauge wire from + terminal on main battery to + terminal on aux battery, and then how does the ground work, does the wire connect the - terminal on the main battery directly to the - terminal on the aux battery? Or does each go to the same ground on the engine? And if so how/where do you connect it?

My setup is very similar to David's it seems so +1 to what he said.

You "can" connect the two batteries together, however, you will see discharge between the two and the batteries will not last. This is especially in the case where the two batteries are not matching (both size, brand etc.) If there are the same battery , you can get away with it, but they will not last as long, as everything you turn off the truck/ solar they will discharge eac hother. I would recommend getting an isolator of some sort, they make plug and play isolators, that are pretty easy to figure out. They automatically connect when it senses a charging voltage from the alternator. You don't necessarily have to have a complicated setup like Davids or mine with solenoids etc. to get to what you want.

 

[4x4junkie]

If the batteries are same brand, same type, same size, and similar age (date codes less than a couple months apart), AND they are located in the same space as each other (I.E., both are under the hood), then there should be no issue whatsoever connecting them in straight-parallel (no isolator).

Advantage:
You have double the usable capacity of an isolated setup for your house loads.
Much simpler setup (less parts to fail).

Disadvantage:
You MUST keep close tabs on your charge level, as draining them too far can potentially leave you unable to start the engine (or carry one of those lithium jump pack gadgets with you).
If one battery decides to go belly-up via a shorted cell (rare, but it can happen), it can drain the other battery with it, also creating a no-start situation.


As for finding a 100Ah grp-34/78 battery... I don't think that's gonna happen.
Battery capacity is directly tied to it's physical size. To get 100Ah you will need to step up to a grp-27 or a grp-31 size battery. You could do two 34/78s in parallel for ~120Ah though.

I run two 27s in parallel for 180Ah on mine.

 

[Martinjmpr]

Well, for me the most difficult part would be finding a place to put the 2nd battery, and with my new-to-me Suburban I'm in luck: Since the 2nd batter was a factory option, I can just order the battery shelf from GM parts and install it in the factory location.
.
Right after I posted my thread above I did a google search that sent me....right back here! :sombrero:
.
http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50
.
I think this is what I'll do.

 

[rayra]

There's an extensive topic on what you want in the 12v/solar forum, complete with explanations, diagrams and a parts list. Total cost for the isolator / relay setup was ~$50 iirc.

The battery tray is $30 on amazon, how much does GMParts want for it?

https://www.amazon.com/dp/B00GTJV9R...=UTF8&colid=QWZ1BSZYG6VW&coliid=IXO5S4I3MVGQG



The tray replaces the corner brace and gives enough headroom for a 75/78 battery, so you can at least have matching batteries if you want.

 

[Martinjmpr]

If you run a normal sized alternator, the isolator should be simple and easy and cost effective... I chose a 300amp alternator since I am running two AGM batteries (odyssey) and the mfg tells me they want to see a hot charge... Up to 10x the amp hour rating... So I went hot... Which jacked up the cost of the isolator...

In use, I went 4.5 days without alternator charging running my 82q ARB refrigerator until I hit "zero" (read 50%) of battery life and I needed a recharge (turn engine on). I only use the aux battery for the refrigerator. I am unwilling to use the main battery for the refrigerator and risk not starting. Given the performance I am getting, it is an unnecessary risk.

D

Wow, 4.5 days is impressive. What was the outside temp? Also, how did you measure the battery life? And I assume you just ran a wire directly from the 2nd battery to the fridge?

 

[Ramblejam]

(i.e. it has both side and top terminals - this was a requirement for me as jump starting with side terminals is a total PITA.)

There's no need for any direct battery connection on these vehicles -- they're equipped with both remote positive (in the red plastic box on the drivers-side front of engine), and remote negative (alternator bolt - marked "GND").

As an alternative, how would I set up a dual battery system?

Depends. What are you trying to accomplish/goals?

 

[rayra]

Here's the topic I was referring to -

http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50

 

[Martinjmpr]

Here's the topic I was referring to -

http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50

.
Same one I linked to in post #6 of this thread. :sombrero:
.
So let me just make sure I understand the setup with the isolator: In the "$50 dual battery setup" there is a 12g wire running from the isolator to a "hot when ignition is on" circuit on the fusebox, right?
.
If I understand correctly, what this does is that when the ignition is on, it "opens" the solenoid so that current can flow between the two batteries, which allows the 2nd battery to charge from the alternator, and then when the ignition is off, the solenoid switches off and the 2nd battery is now isolated so it can't be discharged by the other battery, is that right?
.
So for those that use the 2nd battery to run a fridge or whatever, I'm guessing you have to run a dedicated wire from that battery to the interior or wherever the fridge will plug in, right? And with this setup, I would still be limited to the total AH of the 2nd battery?

 

[Martinjmpr]

If you run a normal sized alternator, the isolator should be simple and easy and cost effective... I chose a 300amp alternator since I am running two AGM batteries (odyssey) and the mfg tells me they want to see a hot charge... Up to 10x the amp hour rating... So I went hot... Which jacked up the cost of the isolator...

.
What kind of alternator did you go with? I believe my (stock) alternator is 160w?
.

In use, I went 4.5 days without alternator charging running my 82q ARB refrigerator until I hit "zero" (read 50%) of battery life and I needed a recharge (turn engine on). I only use the aux battery for the refrigerator. I am unwilling to use the main battery for the refrigerator and risk not starting. Given the performance I am getting, it is an unnecessary risk.

.
So how do you measure the discharge of a battery? I know a voltmeter can measure the volts but how do you know how many AH have been used?

 

[rayra]

.
Same one I linked to in post #6 of this thread. :sombrero:
.
So let me just make sure I understand the setup with the isolator: In the "$50 dual battery setup" there is a 12g wire running from the isolator to a "hot when ignition is on" circuit on the fusebox, right?
.
If I understand correctly, what this does is that when the ignition is on, it "opens" the solenoid so that current can flow between the two batteries, which allows the 2nd battery to charge from the alternator, and then when the ignition is off, the solenoid switches off and the 2nd battery is now isolated so it can't be discharged by the other battery, is that right?
.
So for those that use the 2nd battery to run a fridge or whatever, I'm guessing you have to run a dedicated wire from that battery to the interior or wherever the fridge will plug in, right? And with this setup, I would still be limited to the total AH of the 2nd battery?

Correct in how you mean it, but completely wrong / opposite in proper phraseology. In the electrical world an 'open' circuit is one that is not connected, current will not flow. A 'closed' circuit is completed / continuous / contiguous and electricity will flow.

In that setup, turning the key energizes that selected key-required circuit, supplying power via the small wire to the solenoid (which is a relay, in essence). The supplied power CLOSES the mechanism / switch, bridging the connection and letting power flow.

But conceptually that seems weird to me. especially if you've really run down your 'house' battery'. I wouldn't think you'd want it connected during starting. Only later, while charging.


/I need to fully learn this crap too, on the cusp of a dual / house battery setup myself. My background includes microelectronics, building computers and renovating house electrical, not conversant with the nuances of relays, etc.
/unless I've got it all wrong


Best you go ask your questions in that topic, there's a lot of people with better electrical knowledge that are focused on that subforum and topic.

 

[Buddha.]

.
What kind of alternator did you go with? I believe my (stock) alternator is 160w?

I put a Suburban alternator in my Blazer(puts out more amps at lower engine rpm). I used the 135a unit but I thought a 180 or 185 was available for 2002 model years.

 

[rayra]

The 'standard' alternators options for the early GMT800s are 105A, 130A, 145A. There are aftermarket / custom builds that put out a good bit more and at idle, but those are typically police / emergency vehicle sources and the prices are much higher.


Verkstad, thanks for that. Ive been shy of the ACRs over pricing, but the delayed aspect makes their cost more palatable. But I'm considering a solar option as well as a multi-flavor power module with inverters and various connector types so I can power just about anything. So there's nothing really 'cheap' about what I'm planning.

 

[Martinjmpr]

Alright, so I'm getting down to the nitty-gritty here and trying to figure out which actual parts I will need.
.
Thanks to forum member Jelorian for posting his awesome Z71 'Burb setup! From that I'm thinking that a pair of Blue Sea 5191 terminals to connect to the two positive terminals (since these attach directly the posts it keeps me from having to find a place to screw a fuse holder into the body of the truck.)
.
Next question would the solenoid/isolator. Who can recommend a specific type and brand? And if I wanted one that automatically keeps the starting battery isolated until after the engine is running, which one would I be looking for?