Dual Alternator Setup

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Dual Alternator Setup

August 19, 2019, 11:13:18 am

From the recent discussion about running air conditioners off inverters and the attendant technical challenges, my thoughts have drifted onto the subject of running dual alternators. I searched the Forum and found one old thread pertaining directly to this subject (link below). I would like to revive the discussion and hear any and all current (ha, ha) ideas, both practical and less so. I know we have some smart folks here - many who have extensive boating experience. Dual alternator systems, I understand, are not unusual in the sailing/boating world.

Alternator Talk

I'm not trying to fix anything that is broke. My present electrical setup is working well. My old LN alternator does fine keeping the start batteries topped off. My inverter/charger keeps the house batteries happy when we are plugged in. I have a Trik-L-Start that silently does it's job. I have a new very low voltage drop isolator. I have a magnetic latching solenoid that can be used as a "boost" switch, and also can combine my 3 AGM8D batteries into one single battery bank if desired. See photo below.

Our dash air does not work, and I have no plans to get it working. Our personal preference is to run the roof air (or airs) if necessary when driving, so let's not spin off topic as to why I should fix the dash air. Point is - my engine mounted A/C compressor is not required. Seems the logical spot to mount a second alternator. I think one Forum member (maybe more?) has mounted a second alternator in place of the A/C compressor? Would like to hear pros and cons about that.

In my daydreaming mode, here is what I contemplate. Two alternators, running in parallel. I would move the B+ charging cable from the existing alternator to the START battery post on my isolator. I would run the B+ charging cable from the second alternator to the HOUSE battery post on the isolator. So two separate charging systems - one for each battery bank. My reasoning is this: it would be a simple hookup using existing components, and would provide quick and easy redundancy in case one alternator fails. In that event, (at the isolator) I would simply disconnect the B+ cable from the failed unit, and move the B+ cable from the still functional unit back to the isolator ALTERNATOR post.

I am soliciting thoughts on this scheme, and also the answer to a question. With the engine running and both alternators charging their respective battery banks, what would happen if I closed the ML solenoid and combined the banks? Would the alternators play nice with each other? Would the charging current to the combined battery banks be doubled? Would my whole electrical system explode in a ball of fire?

Bring it on. Would this be a total waste of time (and money), or might it actually provide some advantageous benefit?

Re: Dual Alternator Setup

Reply #1 – August 19, 2019, 11:39:22 am

I don't want to spin off subject on the first post, but to start with you have 2 things doing the same thing in your picture. FET isolator and auto combiner. You only need one of them. As far as the 2 alternators working together I believe whichever one is set to the highest voltage will take over when the voltage of the other one is reached. But let the experts get aboard as I am interested in the ability to run a roof air if needed off batteries.

Re: Dual Alternator Setup

Reply #2 – August 19, 2019, 11:43:24 am

Quote from: craneman – August 19, 2019, 11:39:22 am

..you have 2 things doing the same thing in your picture. FET isolator and auto combiner.

The Blue Sea Model 7701 ML solenoid is not a AUTO combiner...it is a manual combiner. I have a switch on the dashboard that opens or closes the solenoid. It uses zero battery power while in either position, and has a very high current rating, which is why I used it.

ML Solenoid - 12V DC - Blue Sea Systems

Re: Dual Alternator Setup

Reply #3 – August 19, 2019, 11:47:36 am

I have two alts
The second one runs the refer. And house bats .

Re: Dual Alternator Setup

Reply #4 – August 19, 2019, 11:51:43 am

Quote from: Protech Racing – August 19, 2019, 11:47:36 am

I have two alts...

Excellent! I know you are a man of few words, Mike, but could you supply at least a few details? Like specifics on how the second alternator is mounted and driven, and how the charging cables are connected. Photos?

Re: Dual Alternator Setup

Reply #5 – August 19, 2019, 11:53:57 am

Quote from: Chuck & Jeannie – August 19, 2019, 11:43:24 am

The ML solenoid is not a AUTO combiner...it is a manual combiner. I have a switch on the dash that opens or closes the solenoid. It uses zero battery power while in either position, and has a high current rating, which is why I used it.

ML Solenoid - 12V DC - Blue Sea Systems

Sorry mine is a different model. Also no draw when locked in auto mode. it also has the remote manual function.
Now back to the dual alternators.

Re: Dual Alternator Setup

Reply #6 – August 19, 2019, 12:05:10 pm

There should be a pic under the fridge thru the door thread . It mounts in the same belt location as the OE AC compressor .

I did not remove the isolator. Just wired to the other batteries. Maybe I should un hook it , but after a year of non issues, I may leave it as is.
I also use an E bate 1200 watt Pure sine wave inverter to run my baby refer.

Re: Dual Alternator Setup

Reply #7 – August 19, 2019, 12:28:01 pm

A dual alternator setup would seem to be a needed thing if you have added additional, non li-ion batteries, to charge the larger bank at the required 1/5th capacity rate.

Remote battery bank on/off switches would seem to be helpful to separate and then recombine the banks as needed to adjust the batteries amp hour capacity you are charging to match the alternator?

Or a li-ion bank separate from a regular batter bank? Switch one bank in while the other is recharging?

Lots of fun.

I bought a heavy duty slide setup from the link posted here a while ago to allow a couple more mk gels to be added to my existing system if wanted..or needed,

With one alternator would seem to need to switch any extra batteries in and out of the system to maintain the 1/5th C charge rate.

I installed several 110 volt alternators long long ago in several coaches to run roof air(s?) off the engine while driving.

Customers said it worked ok but definitely took away some motor power back then.

4400 watt and 5500 watt were the options long ago,

Re: Dual Alternator Setup

Reply #8 – August 19, 2019, 01:51:56 pm

Our Roadtrek has dual alternators and no generator. Roadtrek calls this their "underhood generator". After experiencing this I would not want it any other way.

The house alternator is 280 amps and controlled by a Balmar MC-614 multi-stage regulator. There is no connection between house and engine battery systems. We could run the house AC driving, but our dash air still works so don't typically do this.

Re: Dual Alternator Setup

Reply #9 – August 19, 2019, 02:33:04 pm

Chuck, just a couple of thoughts, from when I was running my roof air driving in the 1991 U300.

You will need an inverter with enough overload capacity to handle the AC locked rotor amp draw, or put in a soft start system. My 4000 watt AIMS inverter had a 12000 watt overload capacity, which worked fine.

My front roof air would draw about 16 amps at 120V, this converts to about 180 amps at 12V (with inverter efficiency). You will need a healthy alternator, maybe 250 - 300 amp capacity with a little margin for charging the batteries. I had put in a Delco 40SI 300 amp with good results.

This should be an interesting project.

Re: Dual Alternator Setup

Reply #10 – August 19, 2019, 03:10:51 pm

Quote from: prfleming – August 19, 2019, 02:33:04 pm

1. You will need an inverter with enough overload capacity to handle the AC locked rotor amp draw, or put in a soft start system.

2. My front roof air would draw about 16 amps at 120V, this converts to about 180 amps at 12V (with inverter efficiency). You will need a healthy alternator, maybe 250 - 300 amp capacity with a little margin for charging the batteries. I had put in a Delco 40SI 300 amp with good results.

Thanks for joining in, Peter. I was hoping you would show up, since you have already been down this road.

1. I only have a Magnum MS2812, so marginal there...but I ordered a EasyStart 364 (3 ton) soft start module from Micro-Air, which should be here today. I am hoping this will sufficiently ease the strain on my inverter. Won't know for sure until I get it installed.

2. If I decide to pursue this project, I will get the best alternator I can afford. One thing I have noticed while looking at the high powered models online: the big output amp numbers only occur at RPM levels we never see with our diesel engines. The 300 amp 40Si, for instance, makes less than 150 amps at 2000 RPM, which is where my engine feels happiest when cruising. This is why I am interested in running two alternators. I am hoping that if I combined my start and coach batteries, having 2 alternators would give me double the "normal" (2000 RPM) charging amps, and help support my 3 AGM8D batteries during heavy drawdown situations (like when trying to run a roof A/C unit). I am hoping you smart guys will confirm this theory.

http://www.delcoremy.com/getmedia/f651dcc3-60db-4186-80eb-154b8111fdf0/Delco-40SI-Single-Page-Brochure-3-16.pdf.aspx

Re: Dual Alternator Setup

Reply #11 – August 19, 2019, 03:14:55 pm

The pulley size on the alternator might be available with a smaller diameter. Just a thought.

Re: Dual Alternator Setup

Reply #12 – August 19, 2019, 03:18:37 pm

Does the 2000 RPM factor in the pulley sizes with your engine RPM figure? Depending on the ratio between the crank pulley and the alternator pulley, there could be quite a difference in the alternator RPM and engine RPM...
Edit: Craneman beat me to it!
Don

Quote from: Chuck & Jeannie – August 19, 2019, 03:10:51 pm

Thanks for joining in, Peter. I was hoping you would show up, since you have already been down this road.

1. I only have a Magnum MS2812, so marginal there...but I ordered a EasyStart 364 (3 ton) soft start module from Micro-Air, which should be here today. I am hoping this will ease the strain on my inverter. Won't know for sure until I get it installed.

2. If I decide to pursue this project, I will get the best alternator I can afford. One thing I have noticed while looking at the high powered models online: the big output amp numbers only occur at RPM levels we never see with our diesel engines. The 300 amp 40Si, for instance, makes less than 150 amps at 2000 RPM, which is where my engine feels happiest when cruising. This is why I am interested in running two alternators. I am hoping that if I combined my start and coach batteries, having 2 alternators would give me double the "normal" (2000 RPM) charging amps, and help support my 3 AGM8D batteries during heavy drawdown situations (like when trying to run a roof A/C unit). I am hoping you smart guys will confirm this theory.

http://www.delcoremy.com/getmedia/f651dcc3-60db-4186-80eb-154b8111fdf0/Delco-40SI-Single-Page-Brochure-3-16.pdf.aspx

Re: Dual Alternator Setup

Reply #13 – August 19, 2019, 03:19:07 pm

Yes, typically the alternator pulley is sized smaller for a factor of around 3, so at 2000 engine rpm the alternator will be running at 6000 rpm.

Re: Dual Alternator Setup

Reply #14 – August 19, 2019, 03:24:49 pm

SEE! That's why I need you smart guys to guide me! I didn't consider the drive pulley ratio. Eases my mind on that point.

Re: Dual Alternator Setup

Reply #15 – August 19, 2019, 03:26:33 pm

Quote from: Chuck & Jeannie – August 19, 2019, 11:13:18 am

With the engine running and both alternators charging their respective battery banks, what would happen if I closed the ML solenoid and combined the banks?

Would the alternators play nice with each other?

YES, Each will regulate itself according to the load. Subwoofer nuts have paralleled alternators for years.

Would the charging current to the combined battery banks be doubled?

YES, the sum of the alternators, ie 160 + 240 would be 400 amps total avail.

Would my whole electrical system explode in a ball of fire?

NO

Re: Dual Alternator Setup

Reply #16 – August 19, 2019, 04:27:14 pm

Believe this is the same frame size and mounting as the units we use now.
New Blue Bird Bus Alternator AVI160J2004 A160204

Re: Dual Alternator Setup

Reply #17 – August 19, 2019, 06:50:56 pm

We also never use the dash air but if it gets too hot, we run the generator. Easy to remove the compressor and install another LN alternator to match the existing one. Wire that one to the engine batteries less than two feet away and separate the two charging systems all together with the OEM alternator just feeding the house batteries. Get rid of the isolator and install a latching relay in case one alternator goes down.

I have two digital voltmeters, one right below the other so this way, if one alternator fails, I can see it quickly. Running both into a common system means that you are much less likely to see if one fails.

With two of the exact same kind, it would be easy to carry common parts or even a spare. The LN alternator is very reliable and not expensive on ebay.

I just plug in my jumper from one dash lighter plug to the other when camping to keep the engine battery up when the solar is active. The latching relay would do the same and they don't use a juice when in either position.

Pierce

Re: Dual Alternator Setup

Reply #18 – August 19, 2019, 08:40:39 pm

Quote from: jcus – August 19, 2019, 04:27:14 pm

Believe this is the same frame size and mounting as the units we use now.

Interesting. I will keep an eye on it, but they are back-ordered at this time.

Re: Dual Alternator Setup

Reply #19 – August 19, 2019, 09:12:10 pm

As Pierce said, I think IF you intend to occasionally combine battery banks, it is advisable to have 2 identical alternators. This way the alternators will pull together and one won't get overloaded due to slight differences in regulators, etc. In my case with the Roadtrek the battery banks are never combined, and the alternators and regulators are very different. When running the roof air, hit the combine switch, and the alternators will share the load and life will be good. Be sure to match cable size and length as much as possible.

When will you be posting pics? 😎

Re: Dual Alternator Setup

Reply #20 – August 19, 2019, 09:20:47 pm

Quote from: prfleming – August 19, 2019, 09:12:10 pm

When will you be posting pics? 😎

Won't be this week fer sure. Temps here at or over 100 degrees every day. Barely cools off enough to walk the dog at 08:00hrs.

I'll see about matching the alternators. Might depend on what they will cost. Maybe I'll find a "2-for-1" special!

I need to look at how to mount the "extra" alternator in place of A/C compressor. At first glance, doesn't look like it would be "Plug & Play".
The compressor mount is a kinda odd shape and size...

Re: Dual Alternator Setup

Reply #21 – August 19, 2019, 09:40:35 pm

heres how to do it.

Re: Dual Alternator Setup

Reply #22 – August 19, 2019, 09:47:39 pm

Give Nations Alternator a call. They specialize in custom alternator brackets and installations. They did the dual alt system in our Roadtrek.

Nations Alternator

Re: Dual Alternator Setup

Reply #23 – August 19, 2019, 10:49:03 pm

Our LN has two belts but the AC compressor has only one. Just a few things like that including the pulley ratio. I expect a little different problems with each engine but depending on DIY experience, a 2 or 3 hour job plus a trip to a wrecking yard for possible parts. Just need a secure way of mounting it so it can pivot and a way to tension the belts without resorting to a pry bar.

Pierce

Re: Dual Alternator Setup

Reply #24 – August 19, 2019, 11:38:21 pm

Quote from: AncloteJoe – August 19, 2019, 09:40:35 pm

heres how to do it.

Wow! what vehicle needs that many alternators?

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