Alternator and 2 dif types of batteries

Submitted: Tuesday, Mar 28, 2006 at 19:47
ThreadID: 32271 Views:2110 Replies:7 FollowUps:7
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HI Guy's,
Would be interesting to see if people think...or know....if there would be a reason why I could not have a AGM (Absorbent Glass Matt) battery as an auxillary battery, whilst still having a normal wet cell (I presume) 670CCA battery as the main battery for the starting motor.
I have had mixed reports...stating would be not good at all, one being due to alternator having difficulty (of some sort) in charging both batteries, because they are not the same????.
I have a dual battery system (obviously), with the auxillary used only to power a 12v trailblaza fridge (60l). The aux is isolated automatically when the ignition is switched some sort of automatic thingo???.
I am just trying to gain an extra 24 hrs off power for the fridge, before I need to run the car to recharge the Aux Batt, and have had reports that the agm batt may be the way to go.....and is ok to receive a good charge from the alternator compared to a deep cycle, in reletively shorter space of time. Altough, have heard from one source...that its not actually much different???.
If it hasn't been obvious...I am not very techo with electric's....but doing my best to sort it out!!!!!!.
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Reply By: Fr - Tuesday, Mar 28, 2006 at 20:03

Tuesday, Mar 28, 2006 at 20:03
Have looked into the same issue, and it basicly goes like this. If you want to use your aux battery for mainly running your fridge, AGM batteries are definately the way to go as they have the same characteritics as a Deep cycle battery whilst giving quick charging rates similar to a normal wet cell battery. Although they are more expensive to start off with, they have a cycle life of 10 years if looked after properly. I have one under bonnet with a second one in my cabin connected via anderson plug so I can connect and disconnect the cabin one whenever I want. If you look at the Fullriver or Remco brands they are good quality. I picked up a fullriver 120amp hr one for $250 and a 90amp hr one for $210. The alternator wont have a problem charging an AGM battery but you should check whether or not your soloinoid allows for different battery types. The more recent solonoids can charge different battery types and sizes whilst some of the earlier ones didn't like too.
Hope this helps
AnswerID: 163505

Reply By: Member - Mike DID - Tuesday, Mar 28, 2006 at 20:33

Tuesday, Mar 28, 2006 at 20:33
Have a look at this thread

AnswerID: 163520

Follow Up By: Member - Mike DID - Tuesday, Mar 28, 2006 at 20:35

Tuesday, Mar 28, 2006 at 20:35
. . . . and this one

FollowupID: 418229

Follow Up By: Pyalong - Wednesday, Mar 29, 2006 at 13:37

Wednesday, Mar 29, 2006 at 13:37
Thanks for that MIke....I had not seen those post's come up in a search...great
FollowupID: 418376

Reply By: Member - Norm C (QLD) - Tuesday, Mar 28, 2006 at 20:37

Tuesday, Mar 28, 2006 at 20:37
Pyalong, your head will spin with the amount of info available on this subject via a site search.
In my view Fr has it right. I run a vented starter, a vented deep cycle in the engine bay and two 120AH AGMs in the CT. When charging, they are often all connected in parrallel. I've had the set up for a bit over a year and it works great. Certainly no ill effects from mixing batteries.

If the DCs are run down, they take a while to charge ( the DCs are like a 345AH battery when they are parralled). But that is to be expected. I also carry a generator and 25 AMP multi stage charger. My isolator is a simple solenoid. It works fine, but I'd suggest a Redarc or similar voltage sensing unit is probably better.
AnswerID: 163522

Reply By: F4Phantom - Tuesday, Mar 28, 2006 at 21:07

Tuesday, Mar 28, 2006 at 21:07
Was talking to a battery importer (do I need to say it? no link to me) and he was showing me a new kind of battery which I thought was brilliant. It is a deep cycle batt but can deliver up to 1100 cranking amps, from memory that is more than many larger cranking batteries out there. This means you actualy get the best of both worlds, an engine craking battery that also can be cycled without any ill effects. You couldnt cycle a car battery 10 times without ruining it. I reocn put a couple of them in a dual batt setup.
AnswerID: 163531

Follow Up By: Sand Man (SA) - Wednesday, Mar 29, 2006 at 15:05

Wednesday, Mar 29, 2006 at 15:05

New type of battery?..........This is already current technology mate?
Regardless of the Cold Cranking Amps (1100) the battery would have a separate Amp Hour rating and this has no comparison to the battery's grunt.

For instance, Blue Apple manufacture a 105 A/H Thumper which provides in excess of 1200 CCA, so the technology is already existing.

Mind you, you wouldn't want to try and fit it in the Engine Bay as an auxiliary battery. It's a big, heavy bastard and hardly "portable" although it comes with handles.

The 75 A/H Thumper I have provides about 900 CCA, enough to start any 4WD as well as trucks and tractors if I needed to.

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FollowupID: 418405

Follow Up By: F4Phantom - Wednesday, Mar 29, 2006 at 18:00

Wednesday, Mar 29, 2006 at 18:00
yeah i know a little about batts. anyway this batt i speak of is 60A/H and approx the size of a standard car batt. I know other batts are out there but this one does not carry the pirce of an AGM. BTW I have ripped open some claimed AGM's and they are not. Some sellers claim AGM cause it has some matting to hold electrolyte in suspension To me AGM means - blotting paper! I use hawkers for all my needs, made in the UK 51 A/H. I wont tell you where I get em but I pay around 10% or retail. These rock for powering a camp site and I also carry one in the car for the laptop (GPS) charging tools and all the rest with an inverter. I hate generators and really cant see the point of em + you need extra fuel, noise, fumes, WHY???? Batteries also charge via the alternator and have never had a problem, I have seen stuffed batteries bubble and bend but never explode.
FollowupID: 418458

Reply By: Derek from Affordable Batteries & Radiators - Tuesday, Mar 28, 2006 at 21:41

Tuesday, Mar 28, 2006 at 21:41
AGM is the new technology in batteries and will soon be all you will fit. The main thing to remember is that you must check the output of your alternator. AGM batteries want 14V or more. If your alternator is at 13.8 Volts have a new regulator fitted.

Most isolators are on / off and won't know what battery it is charging.

Regards Derek.
AnswerID: 163541

Reply By: Sand Man (SA) - Tuesday, Mar 28, 2006 at 21:45

Tuesday, Mar 28, 2006 at 21:45

Simple mate.

I have been sucessfully running an Exide Extreme (wet cell) as the primary, an Exide Orbital (AGM) as the auxiliary mounted in the engine bay and another portable system (AGM 75 ah Thumper) usually travelling in the rear, but charged from the alternator via its own dedicated in-car charging system.

The AGM battery IS the way to go, if you can justify the extra cost. The AGM will charge faster, more completely and allow a deeper discharge without permanent damage to the battery. Add to this the fact that AGM batteries are sealed and therefore wont spill and can be stored/charged inside the passenger area of the vehicle as they don't generate explosive gases and basically, they don't have any negatives whatsoever, apart from a slightly larger size and a higher purchase price compared with an equivelent deep cycle wet cell.

Any limitation to the contrary would only be the result of a badly designed and poorly performing Controller or Isolator.

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AnswerID: 163544

Reply By: Pyalong - Wednesday, Mar 29, 2006 at 13:38

Wednesday, Mar 29, 2006 at 13:38
Thanks for the input guy's...Brilliant...but I still have a mechanic, who swears black'n'blue...that it shouldn't be'll see how I go.
AnswerID: 163640

Follow Up By: Member - Mike DID - Wednesday, Mar 29, 2006 at 16:20

Wednesday, Mar 29, 2006 at 16:20
Maybe your mechanic has heard the one about the AGM that blew up because it was put in parallel with wetcell battery.

Yes, it can happen. If your Alternator is outputting high voltage (Disco's do it to charge their Calcium Calcium Batteries) and you go for long drives in hot weather the AGM can go into Thermal Runaway. When fully charged it starts drawing more current, which causes it to get hotter which cause it to draw more current . . . . .

AGM's are more sensitive to overcharging when hot. It happens because of the AGM design - they are sealed because the hydrogen and oxygen recombine - unfortunately this releases heat inside the battery ! In a wetcell battery, overcharging also causes gassing but it can escape, taking heat with it, so they have less of a problem.

Have a look at an AGM Datasheet - you should not put ANY charge into them when they are over 50 degrees. Engine compartmenst easily get to 60 degrees.

So when installing an AGM battery, it is even more important to have your Alternator Regulator checked that it is not putting out more voltage than recommended by your battery manufacterer.

FollowupID: 418425

Follow Up By: Alloy c/t - Wednesday, Mar 29, 2006 at 18:13

Wednesday, Mar 29, 2006 at 18:13
Pyalong ,Mike Did loves to put the tech sheet perspective into the scene ,gives him a buzz ,,have run wet cell +Agm underbonnet combinations with no drama , now run and have done for the last 2+yrs an 80amp hr Fullriver AGM Hgl as a starter ,aux batt is same on [oh no according to Mike Did ] exhaust side of engine bay ,,, batteries designed to withstand the freezing cold and extreme heat of space ,, what ?? cant stand the heat of a 4x4 engine bay!!!! buy your AGM you will never go back to a wet cell ..
FollowupID: 418462

Follow Up By: Member - Mike DID - Thursday, Mar 30, 2006 at 07:09

Thursday, Mar 30, 2006 at 07:09
Thankfully most readers will be able to work out how my post explains why your installation doesn't have problems.

FollowupID: 418576

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