Multiple Charging sources

[Kenny]

Can you connect multiple 3 stage battery chargers to a bank of batteries? For instance, 2 Iota 3 stage chargers to a bank of 4 batteries. Intent would be faster charging. Also is there a problem with charging from the engine alternater and at the same time from a multi-stage charger?

Kenny

[Ncbob]

Kenny, let me see if I have this correct.  You want to use more than one battery charger on the same bank in the hope that it will re-charge the batteries faster? Hmmm, why not get a larger charger, would be my first question? What do you hope to accomplish, other than drive the circuitry of each charger nuts?

You might wish to search the archives, changing the search inquiry to suit your particular situation, and see if one of our geniuses has already tackled the problem.

Wish you well.

Bob

[Kenny]

Driving the sensing circuity on each of the devices is what I though might happen. Is this true? What about the engine alternater running at the same time as a 3 stage charger?

Kenny

[Jerry Liebler]

Kenny,
     In a word, the answer to your question is YES.  No harmful effects will occur to either the charger(s) or batteries.  The only difficulty is predicting the charging time, it won't be as fast as simply adding the charger ratings would suggest.  In the case of the alternator and a 3 stage charger the alternator will contribute nothing after the batteries reach it's regulated output voltage.
regards
Jerry 4107 1120

[jjrbus]

 Jerry, Depending on the output of the chargers it seems like that would be way too much amperage going into the batteries?

[JohnEd]

Kenny,

If you were driving merrily down the road with all your engine systems "GO" you would be charging you batteries from the engine alternator.  If you were to fire up the genny to, say, run the roof airconditioner or in my case to recharge the pressure tank with the 115VAC compressor for the criticle need air horns.....would that screw up the charger in the genny that we all have or would it dink up the alternator?  I have done that 50 times or more and it never did me any harm and prior to your question I had not a clue that it might.  NOW I SEE THAT IT COULD HAVE HAD CONSEQUENCES.  Jerry said it wouldn't bother anything and God bless him for that.  I was starting to ponder and worry....really....worry.  Thank you for your question but it was a quick trip to I am OK.  Great to learn that you can use two at the same time and get a little more charge rate.....who knu?

Thanks Jerry,

John

[Sean]

...  No harmful effects will occur to either the charger(s) or batteries.  ...
In the case of the alternator and a 3 stage charger the alternator will contribute nothing after the batteries reach it's regulated output voltage.

I agree with Jerry -- nothing bad will happen (with one caveat -- see my next post, below), but the chargers will "fight" each other (unless they are specifically designed to be ganged) once the batteries have passed the point where they can absorb every amp thrown at them, and you won't get the full benefit of all the chargers.  For this reason, a single 100-amp three-stage charger is better than two 50-amp chargers, for example.  Likewise, two chargers charging two separate banks is better than the same two chargers charging a single bank.

To amplify on his comment about the alternator -- when our chassis/house bridge solenoid is closed and we start the generator, as the batteries move through the bulk charge phase, at some point the regulator on the alternator calls it quits altogether, and essentially turns the alternator off.  This causes our "charge" idiot light to come on, and also cuts out our tachometer, which is connected to the "Relay" terminal of the alternator.  Usually at that point I just flip the switch to disconnect the bridge solenoid.  It's a rare occurrence, though -- the big 6.5kW Delco is so good at both charging the house and running whatever we need, up to and including two of our four air conditioners, that we seldom run the genny while driving, unless it's in the hundreds and we need all four A/C's running.

-Sean
http://ourodyssey.blogspot.com

[Sean]

... Depending on the output of the chargers it seems like that would be way too much amperage going into the batteries?

Meant to catch this one in my last post...

This is a good point.  The answer is "it depends."  However, if you have multiple three-stage chargers working on the same bank, bear in mind that none of them will be able to detect the total amperage actually going into the batteries, and thus, any setting your chargers have for "maximum charging amps" will be defeated.

That said, my presumption would be that the reason to put more chargers on the bank is because the bank is readily able to accept much more amperage than a single charger will deliver.

This is certainly our case in spades.  We have 950 amp-hours of AGM batteries.  Many experts believe that AGM's can safely accept their 20-hour rated capacity in an hour, or, in other words, in our case, we could charge at 950 amps.  Almost everyone agrees that they will safely accept half that amount, or 475 amps.  Our SW4024 will deliver only about 150 amps at full power, and we can get perhaps 230 from the alternator at top RPM (the rest of the alternator goes to running the bus), so the best we can get is 380 amps.

By contrast, flooded batteries should generally be charged at no more than 20% of their capacity per hour.  So if we had, instead, 950 amp-hours of flooded cells, we'd have to limit our charge current to about 190 amps -- more than the SW4024 can deliver, but well within the capability of the alternator alone.

Properly set regulators, by the way, will not deliver excessive current to the batteries, since the charge set-point is a single voltage,  set at or maybe slightly above "float" voltage, and the batteries will generally only accept current at their intrinsically safe rate.  A three-stage charger, OTOH, will continue to increase the voltage until the "max charge current" parameter is met, which is why setting this number is critical if your charger(s) can deliver more than the batteries can safely accept.  In this case, I would advise against using multiple charge sources simultaneously.

-Sean
http://ourodyssey.blogspot.com

[Kenny]

A little back ground as to my intentions.

Eight 8d flooded acid batteries wired for 24 volts
Two 4000w pure sine inverters
Two Iota 45 amp battery chargers
Generator (used only for powering battery chargers)
Bus alternator 270 amp
Four air conditioners
Misc. other 120vac stuff

With all of this, my intentions were to use the battery bank for all of my power through the inverters whether going down the road or parked.

When going down the road, the alternator and if need be the battery chargers (powered by the generator) would be used to charge the batteries.

When bondocking, the battery chargers (powered by the generator) would be used to charge the batteries.

When parked with acess to shore power, the battery chargers (powered by shore power) would be used to charge the batteries.

Regrding battery usage rate vs battery charging rate - I'm sure that the battery chargers would not keep up with the usage if I were to run all air conditioners at once for a very log time. The 120 volt comsumption goes up and down through out the day as air conditioners go on and off. Intent is to provide battery charging to fulfill just above the average battery consumption.

I don't want to be dependant on having to find 30 or 50 amp shore power. Multiple 120 vac oultets at 20amps each are easy to find whether parked at a camp ground or at a friends house.

This is how I arrived at my question concerning multiple battery chargers and the engine's alternater.

Kenny

[Jerry Liebler]

Kenny,
    The posters above who have warned of excessive charging current have a valid point.  Your battery bank will have about 1000 amp hours of capacity.  The usual guidance is c/8 max charging for flooded cells. This works out to about 125 amps, about what the inverters alone can deliver.  I don't know why the recommended charging current is so low.  I suspect it is partly because of temperature rise and partly due to gassing.  If these really are the reasons then it might be a good idea to create the situation where the only circumstance where the current exceeds the recommendation is when the battery voltage is 27.2 or less.this can be done by using the Iotas set up with out 3 stage charging and a simple voltage limit of 27.2 and setting your bus alternator regulator at no higher than 27.2.
Regards
Jerry 4107 1120

[Sean]

...
Two Iota 45 amp battery chargers
Generator (used only for powering battery chargers)
...
Four air conditioners
...
With all of this, my intentions were to use the battery bank for all of my power through the inverters whether going down the road or parked.
...
When bondocking, the battery chargers (powered by the generator) would be used to charge the batteries.

When parked with acess to shore power, the battery chargers (powered by shore power) would be used to charge the batteries.
...

Kenny,

With this arrangement, the most power you will ever be able to use from the genny would be around two kW... that's a really, really small generator for a bus with four air conditioners.

I would very strongly recommend that you look into adding a bypass to the inverter setup (if the inverters don't already have them) so that you can through-power the loads when the genny is running, or when you have 30- or 50-amp shore power available.  You can have a separate pair of 15-amp shore inputs to run the Iotas off smaller shore power when necessary, which is a sort of poor-mans "load support" feature otherwise only available on grid-tie inverters (and a great idea, by the way).

I would then further suggest that you not run the Iotas while driving.  The 270-amp coach alternator is more than enough to provide the max charge rate to your eight flooded 8D's.  If other loads, such as air conditioning, require more power than that (meaning there is not enough alternator left over to charge the bank), then start the generator and let it power the loads directly through the bypass I suggested above, leaving the entire alternator available again to charge batteries.

If you're really serious about only ever powering the loads through the inverter, then you might look into a DC genset capable of producing the same 6.5 kW (or more) that your 50DN can supply (in fact, a 50DN mated to a 10-15 horse motor makes a great DC genny), rather than trying to run the wimpy Iotas from an AC unit.

I think, otherwise, you are asking for trouble, trying to run your whole coach on 2 kW when not driving.  That's just a tad over one household 15-amp circuit.

HTH.

-Sean
http://ourodyssey.blogspot.com

[jjrbus]

 I'll withdraw my post. Sean is much more knowledgeable about this than I am.

[Sean]

Just a thought but running A/C off a battery bank is very inefficent, it is doable. ...

I disagree with this.

We run air conditioners off batteries all the time, which allows us to use a larger, more efficient generator to more of its potential.  In many cases, we don't run the generator at all -- if we drive every day, then we easily make up the battery deficit for our overnight A/C usage from the 50DN while we drive, and stealing 8 horsepower from the big Detroit (which has to be running anyway) for charging the battery is a much more efficient method of deriving the power than running a separate generator of almost any description.

Of course, your system needs to be well thought-out and set up properly to do this.  YMMV.

-Sean
http://ourodyssey.blogspot.com