Dual alternators and dual batteries....

[dokaman]

I have been looking at all of the dual battery threads and other dual alternator threads. I have not found the answer to my question.

I am planning to get two new high amp alternators, probably 180-200 amps each. The question I have is, why not have one alternator for the normall van electrical and accessories and the second alternator dedicated to the house battery and house accessories? There would be no need for a battery isolator or battery switch. It seems like a reliable way to go and gives maximum amperage to charge and run things like the inverter and microwave, while leaving the regular van electrical un stressed.

Thanks in advance for any insight on why this is a great idea or if I am missing something and should not do it.

[daveb]

I guess if the computer has no bearing on what the alternator puts out it would be possible. Two high amp alternators might pull a bit of a load off the engine but I'd think that would settle down after a time as the batteries charge up. Really the only reason I'd like two (if I had the room which I don't) would be to backup the other if one had a regulator problem. On the other hand two means more of a possibility of one having bearing issues on the road. The new high amp aftermarket alternators are better built than the stock types so I'm fine with a single unit. I guess if you already have twin alternators it might be a good move to use a set of high end types. Could be a bit of a wiring project to split them up. To tell the truth I'd rather have a high end multi stage charger being fed off a single high amp alternator taking care of the house system and the separator set manually to the open position as a simple backup if needed. Alternators actually are bulk chargers and don't do a great job of topping off the batteries. I just like everything automatic because having to manually turn things on can go horribly wrong. Even though I have solar, at times the sun just doesn't cooperate.

I wonder how many ambulances have alternator issues being most have twin systems. Interesting project though.

[edit] One of the members has this setup and it is interesting:
http://sterling-power.com/collections/a ... y-chargers

[E350]

Personally, I would like to see comments about the Sterling alternator to battery charger which Dave posted. It may be exactly what I am looking for.

[daveb]

Sure looks cool and high tech. A while back I called them and they claimed they had not designed one for the high amp alternator I have but that was a couple of years ago. Also not sure how it would work with twin alternators but if you were to split them...

[dokaman]

Thanks for the comments so far. That sterling charger does look pretty nice. More to think about.

[boywonder]

I have a basic isolator setup with 2 175ah house batteries and have never felt the need for more alternator output..so far anyway.....seems like when I'm done driving the batteries are topped up to 12.8+V.

I would assume that 90+% of the time a dual high amp alternator setup would be loafing along when you are driving, unless you have some heavy loads running.

For the sake of simple math, if I draw down my house batts 50%, that would be 175ah. If my stock alternator outputs 120 amps, that's about 1 1/2 hours of driving to charge them back up...It also needs to charge up the starting battery after each start so a little more.

It would also seem that higher output alternators would potentially reduce fuel economy but that may not be the case since they would just charge the batteries faster then "unload" the engine while loafing along.

If your use case is high electrical loads combined with short periods of driving (like in an ambulance) then dual high outputs may make sense......keep in mind that the ambulance use case is much more mission critical than van camping as well.

[arctictraveller]

[quote For the sake of simple math, if I draw down my house batts 50%, that would be 175ah. If my stock alternator outputs 120 amps, that's about 1 1/2 hours of driving to charge them back up...It also needs to charge up the starting battery after each start so a little more.

Actually, it will take quite a bit longer to bring your batteries up to full charge as the acceptance rate (the amount of current the batteries will accept) goes down as the batteries reach about 80% charge level. This is why good regulators have three steps, bulk, absorbsion, and float. The first 80% or so of the recharge cycle will go quickly, but then the charge rate begins to taper off quite a bit. The absorbsion phase can take nearly as long to finish off the final 20% as the entire bulk phase took. The result is much longer times to 100% charge than you would suspect. What often times happens is that batteries are not fully recharged between uses resulting in a shorter life span.

As for running two seperate alternator's that are isolated, I see no reason this would not work, but unless you have huge draws on your system, having 400 amps worth of potential current seems like a lot of overkill. I would think, with enough engine hours, one big alternator would work fine to charge up even the biggest banks, as the maximum usable current will fall quite a bit after a while. My boat has 1800 amp hours worth of golf cart batteries (12 6Vs), one 60 amp alternator to recharge the start batteries, and one 100 amp alternator for the house system. I'd like to have a bigger one, but I'm limited to one Vbelt. Still, because we motor for many hours a day, often times the one house alternator is enough to replace all the amp hours used overnight. If we don't motor enough, I simply run the gen for a while to power the shore power charger.

If you install one big, high quality alternator with a seperator or some other method of cross connecting all the batteries, you would save a lot of money and time. If your looking for the ultimate in redundantcy, then two might be one way to do that. Another reason might be to have different charge parameters for different battery chemistrys.

For folks interested in learning more about 12v systems there is no better book available than this one. It's written in simple, easy to understand language. I recomend it to all my assistant engineers as a great referance and refer to it myself often..

http://www.amazon.com/gp/product/007...1&sr=8-1-spell

[E350]

artictraveller: You said:

"This is why good regulators have three steps, bulk, absorbsion, and float."

What do you recommend for a charger?

What do you think of the Sterling as a alternator to battery charger?

Or do you recommend a custom regulator for the alternator? In my 7.3L PSD's case, the alternator regulator is not controlled by the PCM.

(Dang, $39!)

[boywonder]

Artictraveller: Nice explanation!.....I was trying to remain simple in the calcs and not go into the resistance of the load (batteries) changing with charge state.......yes reality is a bit complicated.

[Scalf77]

I think a dual alternator can make a lot of sense if you were to go with a regulator that turns it into a real battery charger. Sterling power also makes them. Also if I was looking into this I would want something that the charge set points could be programmed, especially as the move to lithium becomes more of a possibility.

-greg