I haven't done the homework yet but maybe someone here has an answer... I currently have two alternators on my '98 4Runner, the 1st is the the stock alternator hooked up to a optima yellow top. I added a second alternator from Premire Power Welder and that runs the welder and It's hooked up to my Odyssey PC 2150 battery. Currently the two systems are seperate however I would like to know how to connect the two batteries together for emergency cranking amps or incase I run the main battery dead. I know that I could connect them through a high amp relay/isolator however I read somwhere that you cannot connect two alternators together... Does anyone know how Ford does it on there trucks? Any input whould help, Thanks.

 

When I was doing the car stereo competition thing, it was not unusual for people to have up to 5 alternators (the brackets and belting were engineering marvels). Usually, they just wired them in parallel. It was crtical that they were matched for the same voltage output, though. There is always a small amount of current going back to the alternator (the field), but too much is bad.

While nobody had any real problems with the simple setup, it's probably not the best practice. I would recommend keeping the two systems separate, then having an isolator that could connect the two batteries (possibly disconnecting one alternator at the same time) when you need them.

The really trick setup would be to have a switch that could connect the two systems either in parallel (for more current, starting, etc) or series (for 24V).

 

http://www.hellroaring.com/bic75300.php

Flip a microswitch in the cab and the batteries are joined for self jumping. In the other two positions on the switch they are either isolated except when charging or completely disconnected.

Call and talk to Mike Hines, the owner. Tell him what you are doing and he will discuss your options with you.

 

I talked to Mike at Hellroaring, nice guy. He didn't see a problem having two alternators on one system for temp use. I'm going to use hellroarings BIC-95300B unit and hook up the stock battery to a third optima yellow top, then I'm going to use another hellroaring BIC-95300B unit and hook up the odyssey battery to the third optima yellow top. Both units will be wired up using the backup battery method shown below. The optima yellow top will not have any accessories connected to it and this battery will be the link between my two seperate systems. So my stock battery and alternator will run all of the stock components and accessories I've added to date, The big odyssey battery and PPW alternator will run my premier power welder, winch, webasto sleeper heater, hot water shower pump, prosine 1800w inverter, and other high drawing loads. The optima battery will serve as a primary backup battery, link between my two systems, and aux amps for whenever I may need to tie all three batteries together.

 

I love it when a plan comes together. My Hellroaring unit is working exactly as advertised.

 

Hey Macgyver you got any pics of that dual alternator setup?

 

That is something I would like to see also.

BTW, another dual battery setup:

http://www.12voltguy.com/catalog.0.html9.0.html

 

Sorry for the hijack - Macgyver - do you have a website or pics of your rig? From the list of mods in your sig, it seems like you've been pretty busy...

 

I'm out of town until the middle of January so I can't get any pics until then. I'm going to put together a little website soon. My only New Years Resolution is to finish unfinished projects and the 4Runner is the top of that list.

 

It's late and I can't sleep, all 3 of my cars are out of commision and I'm really inspired to get the 4Runner done so I can ask this chick out that I've had my eye on. She'll be lucky if I make it by the 14th.... Anyways I was in the garage snaping some pics for another post and I took one of my engine bay. You can see the big mammer jammer 4th 8" aluminum pulley mounted on the crank. The alternator had been moved down a couple of inches and the PPW alternator will be mounted in the original alternator location just forward towards the front of the vehicle so it runs of of the 4th pulley. The York is mounted right above the PPW alternator and it also runs off of the 4th pulley. I'll have an idler pulley that will allow be to add tension to the belt. I have finished the design concept and I'm just waiting on my York to come in, I had to send back my Rotolock york 210 for a flange york 210 because I needed the reduction in height to clear the hood comfortably.

 

Do you have pictures of your truck inside and out? It sounds really cool from your sig.

 

I ran across this thread while searching for some info, and I wanted to add some important points. the first is concerning having dual alternators and the warning light output, you will only be able to hook up the warning light output wire on one of the alternators, if you use isolation relays, it's possible to use both, but let me explain why....

The main most warning lamps work (the battery lamp) is by changing the state of the warning lamp output wire, one one side of the bulb, you will have ignition voltage +, the other side of the bulb goes to that warning lamp wire, when the alternator is operating properly, the output of that wire will be +, since you have + on both sides of the bulb, it won't come on, if the alternator stops charging, that output changes to - , when this happens, current flows through the bulb, and you get a warning light.

now back to why both alternators can't have a warning light output, in this scenario, if one of the alternators was working, and one quit, you would have both positive from one wire, and negative from the other, and have a direct short between the two regulators. it's possible to do this with two relays, in this scenario, either relay would cause a ground to the warning light, and it would come on, on both sides of each relay, one side of the coil would go ignition +, and the other side of each coil,would go to each alternator respectfully, if either alternator failed, one of the relays would close, providing ground to switch on the lamp.

if you want to run dual alternators , you really do need an isolator box, the issue isn't voltage, both outputs would be in parallel,just like dual batteries, but the problem is the voltage regulators measuring system voltage, with both alternators running, you have the possibility of voltage feedback, and the voltage could go extremely high or extremely low, you somehow have to have one alternator control the field current for both, one is slaved off of the other, I'm not quite sure on the specifics of that, but that's the best way to do it. It would seem you would need alternators with external regulators, in this case it's easy, to have the field out of one regulator control two alternators fields in sync with each other

 

Sorry to revive an old thread but this is one of the best pieces of information regarding dual alternator setups, regardless of being short of a sure solution.

I'm curious, would "voltage feedback" still be much of an issue if one were using two exact same alternators, running parallel to each other, at the same RPM, and also with a digital volt meter in place to monitor system voltage? The system of batteries and alternator would be as one unit while running and when not running the isolation would separate the batteries in a multiple batt setup.

Two same alts still a problem with voltage feedback?