Who has added a second alternator for house battery charging?

Mex-Busnut · March 21, 2012, 08:57:31 PM

Dear Friends:

I have a pretty normal-looking generator on my engine. This one does not have any oil lines feeding it. It feeds an external voltage regulator. I am attaching a photo. I do not know its amperage, but I just had it rebuilt. (The diode plate was burned up.)

I do have a battery isolator that a friend kindly gave me, but am concerned that maybe the draw on the house batteries, plus the vehicular 12-volt system might be too much for the stock generator by itself.

What would be the advantages of adding a second alternator or generator just for keeping the house batteries charged (feeding the inverter) on the road?

If you add a second alternator, how do you mount it to the engine?

What type of alternator would be best?

Everything on my engine is 12 volts. So is my inverter.

Thanks in advance!

rgrauto · March 22, 2012, 05:58:14 AM

I did add a extra alternator on my 5a MCI mainly because the bus was 24volt. The alt. I used was a 100 amp 80s ford diesel mostly because it was new and just sitting there. I used the old ac compressor mount on the right side to mount the alt. and drive it off the crank pulley. The alt. has an external regulator and you wire it the same way as a truck but I used a GM two wire(connection) oil pressure switch in the oil press. manifold to close a fog light relay to power the regulator. The oil pressure switch is not large enough to power the regulator without the relay, I tested it. The relay puts power to the ( I) terminal on the regulator. If you do this be sure to install a fuse to protect the system. You may want to use an alt. with built-in regulator if you need to buy one. This has worked for me for about five years and no problems so I'm happy! HTH Glen

bevans6 · March 22, 2012, 06:57:51 AM

The decision is less can you do it than should you do it. In my view you add systems and complexity in response to a problem that needs solving. I don't think you know if you have a problem yet. What you could do is sum the total simultaneous loads that you might have, and compare that to the capacity of your current alternator. For example, do you think you will need to run high loads on your inverter while driving, or just power up a TV, or maybe a refrigerator or some lights. Do you expect to have a very large (800 to 1,000 AH) house battery bank, or more like 200 AH. Is your current alternator 60 amps, or 120 - 150 amps?

Those questions and your answers will help you decide if you need to add new systems, or if what you have is adequate. I would stay away from battery isolators, and go with a combiner solenoid if you want an automatic merge of the house and bus batteries, or a simple manual switch (like I have).

Brian

lostagain · March 22, 2012, 07:24:47 AM

When the stock alternator on my Courier 96 died, I replaced it with a 65Amp (IIRC) alternator from the auto parts store that fits GM cars and pickups. It was under $100, and is available anywhere. It works quite well for the old bus. The whole system is 12volt, without very big draws. Of course it would not keep up to a big inverter for say, running a roof AC while driving, but if you don't need a big one, keep what you have and see how it does. A bigger alternator would be better than two small ones.

JC

rv_safetyman · March 22, 2012, 07:32:49 AM

I added a second alternator. It is a typical truck type unit. Mine is a Leece-Neville ( I think that brand is the best). Mine is a pivot mount (some are bolt-in-place) and it has the same configuration as the alternator that came with the Series 60 out of the donor truck.

I am a firm believer in completely separating the house and start batteries. I do have a large quick connect plug that I can use in emergencies, but other than that,they are separated.

The second alternator gives me another level of redundancy in case something would happen to my main engine alternator.

You will need to use something like welding cable to connect the alternator to the house batteries. I always "home run" the wiring - run both positive and negative cable so that I don't rely on the frame ground. YOU MUST have a fuse in the positive cable. I have a 200 ( I think that is the size) amp fuse at both ends.

Jim

Oonrahnjay · March 22, 2012, 07:37:06 AM

Quote from: rv_safetyman on March 22, 2012, 07:32:49 AM(snip) YOU MUST have a fuse in the positive cable. I have a 200 ( I think that is the size) amp fuse at both ends.

Supplier, part number etc.

? Please. Thanks.

Uglydog56 · March 22, 2012, 07:45:21 AM

On another forum I asked this question, and the resolution for someone on a budget in a 12v bus was to install a higher rated alternator with a continuous duty solenoid hooked to an oil pressure switch as described earlier. There are up to 220 amp 12v large frame alternators for trucks available online for 160.00 or thereabouts. These are not brushless alternators, and I was advised to divide rating by three when configuring for max loading. I also do the welding cable etc charging line so you actually get the volts to the battery as recommended by Jim. They also might require a little bracket massaging to fit. If I had a 24v bus and a 12v house bank, or vice versa, I might consider 2 but otherwise it's just more belts to throw. The single big alt/solenoid setup is what I am installing in conjunction with my engine swap. If I am a very good boy, my wife might let loose the cash for one of those 3 stage alternator regulators later.

chev49 · March 22, 2012, 07:56:11 AM

I used the welding cable that the copper strands themselves are 3/4 inch... think its a bit overkill, but had 100' on hand that weyerhauser had in the junk bin years ago....(was used for outside welding)...

Uglydog56 · March 22, 2012, 09:56:42 AM

The first rule of overkill: You can never have too much overkill!

gus · March 22, 2012, 12:48:56 PM

Most second alternators are added to make 12v on 24v systems.

In your case just get a higher capacity alt and mount it in place of your current one, easy out!

My guess is you have a 100 - 150 amp one on now. 150a is large enough for most bus systems but larger ones are available. Mine is 300a and way too big.

Bob & Tracey · March 22, 2012, 01:35:56 PM

Has anyone considered one of these? You would only need one alternator, a big one if you want to run a large inverter.

http://bluesea.com/viewresource/57

http://bluesea.com/category/78/79/productline/388

Lin · March 22, 2012, 01:53:43 PM

As mentioned, the first thing is to determine whether you actually have a problem. My bus has a 45 amp, 24v alternator (which would translate to 90 amp at 12v) and works fine. I would consider putting a larger one in if I was replacing it. An extra 12v alternator could make sense for me, as others, to separately charge the house system. However, I am managing using a Vanner Equalizer to do that. In your case, I would not consider a second alternator even if it were low in capacity. As suggested by others, if you find that you need a bigger alternator, just install one of those.

gus · March 23, 2012, 01:19:32 PM

I replaced my 4104 three wire 150 amp Leese-Nevill alt with a 100 amp one wire. It is fine except when all lights and monster original heater blower are on, then it can't keep up. It doesn't lose much, but some.

Since I never have the blower on all the time it works OK. After the blower the running lights seem to take the most power.