dual alternators...

My -twin batteries, split charge- charging system is underpowered. Instead of uprating the existing alternator, maybe I could use the spare one that's lying on the shelf. Get rid of the diodes and build two independent charging systems... I also have an A/C bracket that repositions the PAS-pump and probably could give the second alternator a space of it's own. Anybody done this?

Thanks for any input.

Reply to
aghasee
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Sorry if this sounds patronising, but exactly what's the problem with your current system? There's lots of possible reasons why it's not charging your batteries correctly, and adding another alternator isn't guaranteed to fix them all.

Reply to
QrizB

"QrizB" schreef in bericht news: snipped-for-privacy@news.easynews.com

1) The batteries used have different capacities. 2) The discharge loads are not equally divided. 3) The alternator IS underpowered.

The voltage loss over the diodes is compensated for, if that's what you mean...

With a dual alternator system I would...

1) ...virtually double the charging capacity? 2) ...use the correct charging current for each battery? 3) ...have a more efficient system?
Reply to
aghasee

It's getting late, so please excuse me if the following is a little confused. And, as always, it's my opinion and I reserve the right to be utterly wrong :-)

This shouldn't be a problem, so long as they're both based on the same technology (lead/lead, lead/antimony, lead/calcium, AGM, gel, whatever). If not then I'll agree that yuo need two separate charging regimes.

This shouldn't be a problem with a single alternator.

You're the best judge of this, but you can only charge a battery so fast. Unless you've got more battery capacity than ~5x your alternator output, adding another alternator is unlikely to help (subject to your power consumption when running being something typical, rather than a FOAD stereo system or enough lamps to melt steel).

That's not what I mean, but thanks for confirming it.

Yes, but unless you do something to get this charge into your batteries it won't help. There's only so fast you can charge a battery, and generally with automotive batteries once you can only manage a sustained charge of about C/5 (that is, one-fifth of the battery's capacity per hour) at the 13.8 to 14.4 volts that most alternators are limited to. AGM and spiral-cell batteries (eg. Optimas) manage to take charge faster, but it still takes a couple of hours to charge them.

And you'll only get to 80% charge in any reasonable time regardless.

Well, no, not really. As mentioned vehicle alternators spend most of their time running in their voltage-limited mode, rather than delivering their maximum rated current, as the battery controls how much current it can take.

I would expect that your only efficiency gain will be by doing away with your splitting diodes.

If you haven't read it before, you might like to glance over William Dardens FAQ,

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and see what he has to say about charging.

Reply to
QrizB

1) Assuming the alternators are the same, yes 2) Yes, each alternator would output the charge to the battery, and thus just charge that battery 3) Well, more efficient than a split-charge, which by it's nature doesn't chare both batteries at the same time.

Word of warning: Under NO cirumstances have a connection between the two alternators, either intentionally, or via a unit connected to them. It will generate a standing current and will do all sorts of funny things. You could couple them for starting if you wish, but the connection should be broken as soon as the engine fires & the alternators start working (ie via a solenoid in parralel with the starter.

Alex

Reply to
Alex

"QrizB" schreef in bericht news: snipped-for-privacy@news.easynews.com

Indeed, tomorrow i'll read the batteryfaq, maybe there are other solutions. Oh, and what's a FOAD sound system? :-)

Reply to
aghasee

"Alex" schreef in bericht news: snipped-for-privacy@4ax.com

They are identical units.

Seems only logical.

Which would also be eliminated with a dual alternator.

Of course. I have rewired the Ruster completely last year. It has two fully separated circuits.

Reply to
aghasee

Something to do with going away in short jerky movements, and then ceasing to be :0)

`Mark

Reply to
Mark Flint

FOAD -- a former manufacturer of automotive audio equipment, based in Belgium and contracting the manufacture to various Far-Eastern suppliers, reputedly based in Taiwanese garden sheds. They claimed to have the most powerful production systems on the market, but had problems with power wiring, speaker balance across the audio range, and radio tuners. A typical FOAD rig would put out hardly any sound above

25Hz, had power leads which tended to either glow red or burst into flames at the battery, and could never tune to the same radio station for more than about 15 seconds. Customers can be recognised by their bulging eyes and a tendency to say "Wha'?".
Reply to
David G. Bell

On or around Mon, 12 Jan 2004 22:51:22 GMT, "aghasee" enlightened us thusly:

bigger alternator would solve the last, and if the split-charge system is working right then the first 2 shouldn't be a problem either.

note that the only time your alternator capacity is a problem is if you're running a lot of lights etc at low engine speeds, such that almost all the alternator output is going into the running load and dropping the overall voltage down below about 13 - otherwise a discharged battery will grab it's share. The internal resistance of the battery is very low.

well. 1) depends on the sizes of alternators... the second one, if it's charging a battery for leisure or caravan use, needn't be big. However, read on...

2) well, yes and no. If you separate the non-vehicle thing completely, then the vehicle electrics won't steal current that would otherwise charge batteries, but see above about alternator output. 3) yes, but only slightly - as Qriz says, the only notable gain is in removing the splitter diodes.

However, I think the biggest advantage is the one you've not (apparently) noticed, and that's that if you mount 2 alternators, then if the main vehicle system one fails, 5 minutes changing connections to swap the vehicle charging side over to the other alternator gets you back on the road... provided, of course, that the 2 alternators are near enough the same size.

I think you should be able to get away with a common earth, which is difficult to avoid. You then need, for the "leisure" system:

1) Fat wire (5OA capacity, say) from the alternator output to the battery + 2) Thin wire through a relay to the alternator rotor terminal. 3) make sure that none of the "leisure" side loads are cross-connected to the vehicle system, and obviously, remove the + link between the batteries.

the relay in 2) has to be energised by the vehicle ignition, so that it doesn't drain current through the alternator when the ignition's off... just like the normal alternator has. Optionally, put a no-charge warning lamp in series with the relay switch, so you can check that the leisure battery is getting charge. Optionally, a second voltmeter on the leisure battery as well.

Reply to
Austin Shackles

This is done all the time on boats. Keep the circuits totally separate and you'll have no problems. It's as easy as you think Cheers, Peter

Reply to
Peter

I've currently got twin alternators on my motorhome i'm building,

i have decided to do this because i dont want to use antoehr split charge system, yes for most people they work fine, either relay, manual switch or diodes etc,

but i'm having 330 AH's of leisure battery, and have a 90 amp hour starter battery, a single alternator will struggle to charge them up properly.. especialy if i use a switch or relay.. the leaisure batteries will never get a decent charge, and the starter battery could well be over charged.

i'm also going to be putting a sterling inteligent alternator regulator on the leisure battery alternator, no need for that featur on the starter battery, as i dont need the starter battery to give out all the power it's got, where as i want to get all the power i can from the leisure batteries.. which i'll never do if they were split charged, or fed under 14 volts which the voltmeter on my dash always shows is happening when the lights are on.

Anyway, i'm currently updating my web site, doing the split charge pages now (i write technical type articles for motorhome self builders) so am doing the split charge options first, but given a few days i'll have the photos and reasons for my twin alternator set up on the site, (ok the van's an Iveco, but anyone with some welding knowlage and an eye for detail can get a second altarnato mounted on their engine.. providing it's not one of these modernt things where you have to take off 20 plastic covers just to get at the oil filler :)

i havent got my van with my right now, (its having its new body built) so the second alternator just sits there without a drive belt at the moment, but as soon as i get the van back, the leisure batteries are going in, the

400 amp welding earth cable goes from the batteries to the engine bay (a 6 meter run) a solenoid going on the end of hte cable from the leisure batterie's positive terminal (negative termianl goes to chassis earth back at the abtteries location) the alternator output (90 amp bosch jobbie) goes to the wire to the battereis, the other connection on the solenoid goes to the starter battery, Switch on the dash operates the solenoid to connect the leisure batteries to the starter for emergancy starting if needed.

a second volt meter on the dash with a built in no charge warning light will go in, and the no charge light will supply the exition current to start the second alternator charging,

jsut need to find out if running the exitation current to the field windings of the second alternator off power picked up from the starter battery will be ok (via the ignition switch), or if it needs to be from the leisure batteries, and thus via a relay.. got too many of the buggers as it is, so one less relay will be helpfull.

btw, anyone interested, my site is

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the Kamper tech pages are prolly all your interested in, unless your also building a motorhome :)

Reply to
CampinGazz

I wouldn't do it. The light goes out when the excitation terminal is at alternator output voltage, matching battery voltage. If you fed it from the other battery you'd have a link between the two systems, which could do bad things, and the warning light wouldn't tell you anything useful about the leisure battery.

Remember that FFR Series Land Rovers had a special double alternator with two independent 24v systems.

Reply to
David G. Bell

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