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Old 06-08-2018, 03:55 PM   #1
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2 Alternators CAT 3126

Has anyone added a second alternator to their CAT 3126? I have been trying to avoid it and go with a 12v solar system, but it seems like all the solar stuff will work better with a 24v system and therefore I need to add another alternator. Info on doing so would be highly appreciated!
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Old 06-08-2018, 06:53 PM   #2
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If you are already doing solar why not use a voltage step down? They are less money than adding an alternator. I guess I don't know what you need extra 12v for
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Old 06-08-2018, 08:36 PM   #3
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Our panels will not be exposed when driving. We were planning on using the alternator to charge the system while on the road. So, would I need a step up? Alternator > step up > batteries


I have no clue what I am doing with solar and it has been somewhat difficult to know what we need. I am looking for someone to take over and tell me EXACTLY what we need.



Thanks for the response!
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Old 06-08-2018, 09:53 PM   #4
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https://www.solar-electric.com/ Great site to educate yourself about solar, options and figuring out what you need.
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Old 06-08-2018, 09:57 PM   #5
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https://www.solar-electric.com/ Great site to educate yourself about solar, options and figuring out what you need.

Yes, I have read over that site, and many others. Not everyone can read a book and know how to do something. Try to rebuild an engine by reading, it doesn't work. Take it apart, screw it up, take it apart again, and rebuild it. I'm very much hands on, but without having the items I need I can't be hands on. I'm about to finish a BS of environmental science and we've barely touched any rocks or been in the field.
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Old 06-08-2018, 10:16 PM   #6
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Victron makes a charger that will charge your 24 volt battery from a 12 volt source.

The 20 Amp version costs about $150
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Old 06-08-2018, 10:17 PM   #7
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We had planned to wire for 50 amp service.
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Old 06-08-2018, 11:03 PM   #8
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Learn how to do an energy audit.you can practice at home. All you need is pencil and paper. This is the basic first step to designing any solar system be it rv or marine.
Learn the terminology.
Watch you tube.
Good luck
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Old 06-08-2018, 11:28 PM   #9
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Our panels will not be exposed when driving. We were planning on using the alternator to charge the system while on the road. So, would I need a step up? Alternator > step up > batteries


I have no clue what I am doing with solar and it has been somewhat difficult to know what we need. I am looking for someone to take over and tell me EXACTLY what we need.



Thanks for the response!
I'm not sure on that, I would to be safe.
I believe you can feed lower voltage in but it's way less efficient

How many amp hours of batteries are you planning?

What's the output of your current alternator?

What is the percentage of time you would have the panels covered while driving?

I would think you'd be better off with a generator or letting your bank charge before leaving
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Old 06-09-2018, 04:57 AM   #10
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if you are going to install a second alternator and your battery bank input is isolated from the bus electrical system then install a 24V alternator rather than do step-ups..

-Christopher
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Old 06-09-2018, 09:55 AM   #11
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if you are going to install a second alternator and your battery bank input is isolated from the bus electrical system then install a 24V alternator rather than do step-ups..

-Christopher
Hi Christopher
Have installed second alternators on a few 4wd and am currently installing one now on my 5.9 Cummins. The Cummins is fairly easy because the second alternator is going where the second A/C compressor was. The other ones were done by holding up the alternator where it would fit and had something to bolt to and then welding up a mount piece by piece.Time consuming, sure, rocket science no.
Also the second alternator on the 5.9 will be dedicated to house batteries only so the engine charging system is isolated.
Will be going to work on it today and will take a few pictures. Certainly agree on a 24v system if you are going for a larger system.
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Old 06-10-2018, 09:05 AM   #12
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I'm not sure on that, I would to be safe.

I believe you can feed lower voltage in but it's way less efficient



How many amp hours of batteries are you planning?



What's the output of your current alternator?



What is the percentage of time you would have the panels covered while driving?



I would think you'd be better off with a generator or letting your bank charge before leaving

I'm not sure how many amp hours of batteries we are going to use, but likely around 1000 since I want enough to keep us going if it rains for a week.

The current alternator is 12v I believe. Is there an easy way to check?

The panels would be covered 100% of the time while driving.

We want to stay away from using a generator to charge since we spent a good amount of money on solar.
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Old 06-20-2018, 08:11 PM   #13
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Hi Christopher
I have a 14 HP riding mower engine which has electric start that I will hook up to a alternator .Your fuel mpg I'm sure is not that great , now you want to add something that going to suck more power from the engine . I was spinning an alternator up with a drill then energized it ,it yanked the drill out of my hand ,and that was just a 50 amp auto alternator .I've seen ratty mowers with good engines for $75 .
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Old 06-21-2018, 08:01 AM   #14
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ultimately energy is simply modified.. efficiencies definitely vary in many methods but making electricity requires energy whether it comes from a secondary engine or the bus main engine.. or from roof-top solar panels. I like the idea of a pony engine (a diesel one) for running various components.. it gives the ability to run these components while driving and while parked. flexibility.. solar on the roof for those bright sunny days.. and a pony engine with a 24 volt alternator (and an A/C compressor) for those cloudy days.. and for having A/C while you drive..



im not sure id use a mower engine.. they are definitely cheap but if all im doing is generating electricity with it im likely to just go get a generator and mount it in a nice enclosure under the bus..


if im going pony engine id likely want a diesel so I can carry one type of fuel..


-Christopher
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Old 06-21-2018, 11:24 AM   #15
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I like the idea of a pony engine (a diesel one) for running various components.. it gives the ability to run these components while driving and while parked. flexibility.. solar on the roof for those bright sunny days.. and a pony engine with a 24 volt alternator (and an A/C compressor) for those cloudy days.. and for having A/C while you drive..
Oh, that's a GOOD idea! What you're talking about sounds a lot like scaring up an APU from an over-the-road rig and adapting it.

The only drawback I see in the first 30 seconds of thinking about it is that now your inverter becomes the bottleneck. Instead of sizing it for the "over loads" (above and beyond what the baseline battery bank can supply) you'd have to size it for the entire expected peak load, since it's the only source of 120VAC onboard.
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Old 06-21-2018, 11:58 AM   #16
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Oh, that's a GOOD idea! What you're talking about sounds a lot like scaring up an APU from an over-the-road rig and adapting it.



The only drawback I see in the first 30 seconds of thinking about it is that now your inverter becomes the bottleneck. Instead of sizing it for the "over loads" (above and beyond what the baseline battery bank can supply) you'd have to size it for the entire expected peak load, since it's the only source of 120VAC onboard.


Thatís basically how I use my onboard generator. My inverter is an automatic transfer switch and charger so I produce 120 V that gets converted to 12 V for charging versus the model that youíre suggesting with creating 12 V that is inverted to 120 V. It seems like it would just be safer and more efficient to go with the higher voltage for the longer runs.

It is really nice to be able to shut down the bus when you stop somewhere and continue letting the air-conditioners run.
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Old 06-21-2018, 12:26 PM   #17
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Thatís basically how I use my onboard generator. My inverter is an automatic transfer switch and charger so I produce 120 V that gets converted to 12 V for charging versus the model that youíre suggesting with creating 12 V that is inverted to 120 V. It seems like it would just be safer and more efficient to go with the higher voltage for the longer runs.
So you're running a more conventional "genset"? Produces 120VAC which you then use both for charging (by feeding a charger that downconverts it) and for powering the 120VAC side of your bus systems? That is what I'm thinking of as the more "conventional" or "baseline" approach.

What Chris suggested, and I jumped on, also provides an alternate AC compressor. I'm not sure if on-the-fly changeover from one compressor to another is feasible or even possible, or if I'd be limited to running the A/C off that one compressor.

I'm interested in why you use the words "safer" and "more efficient". Easier to comprehend/design, for sure, but I don't see a clear advantage to either setup for those two metrics.
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Old 06-21-2018, 02:44 PM   #18
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you use a separate A/C system than your electric.. the idea being if you are running your Genset already for A/C then the pny engine is no different, it is just you are taking engine power and using it to drive a mechanical compressor rather than going mechanical-power => Electricity <= Mechanical power. for people runnon on batteries or solar then this A/C (Aircondition.. AC = Electric. A/C = Air-COndition)solution isnt a good one..

-Christopher
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Old 06-21-2018, 03:51 PM   #19
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OK, Chris, I'm not smart enough to figure out what you're saying here. The reason I jumped on this was the idea that I could get a twofer out of one aux engine - "generator" even at 24VDC and not 120VAC, and A/C compressor.

Upon reflection, I'm not sure that buys me all that much. I had a question about the feasibility of running one A/C system off of either one of two compressors; i.e. "choosing" which compressor was doing the work. After trying to use Secret Agent Google to answer my own question, it appears that the answer is "No, you can't do that." In other words, the refrigerant loop from compressor to evaporator and back is fixed and unchangeable; you can't put electrically operated valves in it to route the refrigerant one way or the other.

So if I put in a surplus APU I would have the choice of either needing to run it 100% of the time I wanted that particular A/C to be working, or deleting the compressor off it and calling it a generator. This is still a possibility - it would be a (24VDC x 65 amps = 1560 watts) diesel powered genset for a grand or less. Pull the compressor and put in a second alternator and you could get 3-4 KVA out of the deal.

For $1000-1200 it's still worth considering. About half the cost per kw as buying an Onan diesel rig. Since my "genset" would not put out 120VAC I'd need to upsize my inverter accordingly. But I wouldn't have to go through any hoops to get all the 24VDC I wanted to recharge whatever battery bank I had. A 4kw pure sine wave inverter can be had for less than a grand.

I'm still trying to comb out the design ramifications. Presumably both the battery bank and the solar array would drop out of the equation since they are what they are either way.

Maybe we need to move this thread into electrical. Maybe I'm the only one interested; I don't know.
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Old 06-21-2018, 04:15 PM   #20
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you CAN put electric valves into an AirCon system but the issue is where will the oil end up.. there is oil running around with the refrigerant... depending on system load.. (a sudden cold rain hitting your condensor Loves to trap the oil in the condensor.. this clears itself in a matter of a short time so nothing gets hurt.. sometimes much of the oil is in the compressor.. if I run enough oil to keep 2 compressors lubricated even though only one is running. i run the risk of oil slugging the system. (oil doesnt evaporate and condense.. so it is actually detrimental in the cooling abilites.. its a necessary evil..).. or the other way.. all the oil gets trapped in the running compressor you just shut off now the other one has nil and burns up..


the original thougbt in this thread is to be able to use the Bus engine to generate enough electricity to keep the house batteries charged and all desired electrical appliances operating.. when parked the use of solar does this..



it morphed into generators and AirCon and everything else.. I chimed in on the fact someone mentioned a 14 Horsepower gas engine to run the AirCon and charge batteries.. a pony engine (diesel) makes sense if you only want to have one means for charging and for AirCon.. ie you boondock all the time and dont have the need or want for solar.. so it acts as your APU and can also give you road Power and AirCon as well.. its a built in generator essentially..



the pony engine doesnt work if you want ot also use electric AirCon. ie campground or using solar / batteries... in my opinion if you want AirCon on the road you keep at least one of the Bus;s original road units or you snag one from a texas / arizona / florida junkyard.. ultimately minisplit electric AirCon units are much more efficient than a pony engine spinning a compressor and a big alternator.. but if thats the way you plan to travel than that extra engine makes sense..



-Christopher
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