2500HD Alternator ?

lauriet1 · May 15, 2002

I just finished having all the wiring, isolator/relay and tray installed for an under the hood Auxilliary battery. The BATTERY STORE is telling me that I need to put in a new high output alternator in order to charge ANY type of second battery I put in the truck whether it's a deep cycle battery or standard starting battery. I have a 105 amp alternator. Do I really need to replace my alternator or is this BS?

gandolphxx · May 15, 2002

It is a good idea to upgrade that 105 to a 200 with the second battery going in - depends why you have the second battery - if you are running a lot of stuff with the engine off, you are going to put a lot of charge load on the alternator when you are back driving.

lauriet1 · May 15, 2002

Thanks for the input. To clarify.....I'll be running a fan on a thermostatically controlled propane furnace in a 2001 model year slide in camper. The fan only draws 3.4 amps. Everything else in the camper will be run on propane. Would an intermittent 3.4 amp draw on an aux battery be justification enough to warrant a new hd alternator?

2k1 2500hd · May 15, 2002

In my honest opinion, you do not need a larger alternator. I tow a travel trailer with 2 6-volt golf cart batteries hooked in series (12 volt). The standard alternator charges both the truck battery and the house batteries fine. You installed an isolation relay, so your truck battery should not run down. Also depending on the type of isolation system you installed, the truck battery always gets the charge first then the camper house battery.

Bruce

lauriet1 · May 16, 2002

Gand and Bruce: Looks like we have a 50/50 split decision. I will forgo the bigger alternator for now. Based on my usage I really don't think I need to beef it up. My apologies for pushing the panic button. Being new at this, I'm getting all sorts of info and I don't know who / what to believe. I want to be sure I don't ruin my truck but I also don't want to be taken advantage of either. My pockets aren't that deep right now. I am a female truck owner, but I'm not stupid. If I need information on something I'm unfamiliar with, I come to this forum to get it! That's for my own protection and peace of mind...Thanks All!

TomEllis · May 16, 2002

Lauriet1,

What is the current rating on the isolator that was installed?

if it is rated at 120 Amps, then the Alternator that you have is fine. You do NOT want to put an Alternator on your truck that is higher output rated than the Isolator.

Tom Ellis

lauriet1 · May 16, 2002

Tom - Oh Crap - The isolator indicates Max. Alt. Amps. are 95. GMC Parts said the Alternator on the truck is a 105 amp based on my Vin# so...looks like I'll have to get another isolator huh? I'm going to take a look under the hood again tonight and check the alternator myself. Will it indicate the amps somewhere on it? Is there anything else I should look for under there while I'm at it?

No big deal if I have to swap the isolator out. The guy who installed it said he'd just exchange it for the right one. He also said he checked everything out and had put the right one in though. Oh well, good thing I'm asking questions here. God knows where I'd be without this place. :inlove:

Colorado Kid · May 16, 2002

My truck came with 2 batteries and a 105 amp alternator, so I think you'll be fine there.

The only way you could hurt that isolator would be to have the aux battery completely dead and the main completely charged when you start the truck, causing full rated output of the alternator to go to the aux battery, so you'll probably be OK, but if the guy will fix it for the difference in price you might as well go to at least a 105 amp isolator.

A few of the D-max owners have added the (factory optional) second alternator, but I don't think you've got anywhere near enough load to justify that.

seatec · May 17, 2002

like lauriet i'd like to know where on the Altenator i can find its Amp output. What is the standard isolator APm on a 2002 D/a 2500HD?Thanks for the info

lauriet1 · May 17, 2002

seatec - I looked at mine last night. Stand on the driver's side front quarter panel, tilt your head slightly to the right and look at the side of the alternator that's facing you. You can see the amps stamped in the metal. It's kinda hard to locate the stamp, but it's there. Mine is stamped 105A. My Isolator will be swapped out this weekend!

Colorado Kid · May 17, 2002

like lauriet i'd like to know where on the Altenator i can find its Amp output. What is the standard isolator APm on a 2002 D/a 2500HD?Thanks for the info

The Alternator on your truck is 105 Amps, just like mine.

We have no "standard isolator". Both of our batteries are connected to everything all the time. The isolator is to keep the camper from draining the "main" battery on a gasser to the point that it can't be started...we have no such protection on our rigs, so the camper should be unplugged from the truck when the engine is shut down for an extended period,.

JimDandy · May 20, 2002

No need to change the isolator, the 95amp one is just fine, even though the alternator puts out 105 amps (max output) the engine, computer, and anything turned on (lights, heater, A/C, etc.) all draw from the alternator, too. Even if the alternator is maxing output, and the auxillary battery was completely drained, I doubt the isolator would see more than 50/60 amps, given the draw of everything else.

Oh, BTW, the factory dual battery set-up comes with the same alternator, so don't bother changing it out, unless you are adding something with a high-amp draw (welder, snow-plow, winch, etc.).

Just my 2 cents worth.

James

MarkD · May 20, 2002

Does anyone have pics of a factory dual battery install?

What comes in the "wiring kit" from GM, or can you get one?

Part #?

Thanks

seatec · May 20, 2002

Thanx lauriet and Colorado.

lauriet1 · May 21, 2002

The install is complete! Went with the regular Battery kept the 95 isolator for now. Everything works, heat, fridge lights. I wanted to thank everyone here for their input once again. You guys are the best!

MarkD - Check out the other Aux Battery Question Thread. I posted a link there with pics. It's an aftermarket install, not factory, but it might help you out.