Second Battery Charger

[Never Again II]

This question probably should have been investigated before the install, but I haven't plugged in shore power, yet. Our boat has a factory 15 amp 2-bank battery charger running to the battery switches for both banks. I have been wanting to install a 1500W inverter, which is my next project. Also have an aftermarket 20 amp, 2-bank charger that I have been wanting to install before the inverter to make up for all the extra power pulling from the house batteries. I installed the charger today and ran each wire pair straight to a battery bank, 1 to a house battery and 1 to an engine battery. All 3 house batteries are paralleled as are both engine batteries. My question is whether the two chargers will interfere with each other's operation.
Will this configuration work or do I need to run one charger to the house batteries only and the other to the engine batteries only?
I like the thought of having 35 amps of charging capability if needed for whichever bank needs it, but I am not sure if the chargers will actually work this way. I have been unable to find detailed enough info about chargers to figure this out.

[heymagic]

I'll hook up a couple of chargers at the shop and see. Sounds like a bad idea though, I bet the regulators won't be happy. I know if we start a car with the battery charger hooked up many will start flashing the charge lite .

[SomeSailor]

My question is whether the two chargers will interfere with each other's operation.

Yeppers. They'll see each other and not be able to get a sense on the battery. Most chargers (3 or 4 state) actually test the battery when they first come on by applying a load and watching it for a few seconds. If there's another charger in the circuit, it would supply that load and the original charger would think... hey.. no charge needed here.

I still say your best approach is one thats not so automated. Rig up some A/B switches and an A/B/ALL switch you you can route power wherever you want.

That's the big heated debate between Doug and I over at BOC right now. By tying all that stuff together, you lose the ability for anything to sense the individual batteries. If I were doing what you are trying, I would want the ability to switch in (or out) any battery (or bank) that I wanted at any time, and be able to charge them the same way. One at a time, or separate.

In that scenario... you could have ALL your batts dead... and only need to get ONE battery charged enough to start the boat. Then you're on the road again.

[heymagic]

Batteries aren't self regulating as some think. If you have a low battery and a good battery tied together and charging, the low battery will pull from the good battery also. The regulator won't know how much charge is where and will keep pouring out all it can. Both batteries will be boiling before long. Everything I've read in print says when tieing batts together use the same brand and size so they can be equalized.

I think you can use two chargers ok, but keep them totally seperate. Of course you'll be losing some more of that 30 amp shore power. Generally though, you won't use the inverter much at dockside, nor will the engine charge that many batteries underway. You may be engineering in the wrong area. At dock you're usually tied up for 16 hrs or more , plenty of charging time. Underway is usually 4 hrs or so, not much charging time. At anchor or a state park 110v chargers do no good.

I would use one good charger, 30a, 3 bank. Then get a monster Balmar 120ish amp alternator and isloators or combiners for underway. That's really when you may need the extra charging power.

[SomeSailor]

There ya go...

... and that way you're not sitting there scratching your head wonder which of all those batteries you need to replace.

Most folks are taking advantage of how a batteries internal resistance increases as it gets closer to charge and thinking somehow that's regulating. It's really not. You apply 14V to a battery... and current will flow. That isn't good for a fully charged battery.

Think about when you need all this power. Like Gene said. If you're charging your banks at 120A and discharging at 10A on the hook... that's 12 hours of use for every hour of running.

Maybe you need a little Honda genset for Fathers Day?

[sunnydude2]

Can i ask a question on the alternator? Even if you get a 120amp charger, you don't get 120amp output at idle right?

SS...if i added this to my plan would it help?

[SomeSailor]

I think following Gene's advice is probably the best thing you could do. He's been doing this for a lot longer than I have and as a professional, he's got lot s of years of actual experience.

Wouldn't that be a lot easier than a sophisticated bank of switches and batteries? Besides... you'd be able to recharge in no time and worst case start the motor to run the invertor. A 120A alternator would produce well over 1400 watts. More than enough to keep up with an invertor that was maxed out.

To answer the idle question, most have a field voltage taht will collapse at a certain level. I don't know at what point it would drop out if you had it maxed out at idle. I don't think it would be a problem because the batteries are acting as a huge buffer.

Remember the alternator is just trying to refill the batts. So it won't feel the current load of the invertor all the time anyways.

[Randygh]

Mike and Gene--I have 3 batts (starter, 2 house, all 12volt). The house batts are the same and the starter is alittle bigger. I have the starter battery isolated from the two house batteries with an on/off switch and the house batteries are separated by a one/two/both switch. When on the hook I switch off the starter battery and use the house batts, one at a time. My charger is wired to the switches in such a way that I can charge one or both house batts or starter battery. When running, I can switch off the starter battery and charge one or both house batts and/or starter.

2 questions: 1.) Is there a such a thing as a percent charge gauge that I could wire to each battery and control with 3 individual on/off switches to monitor the batteries' charges. 2.) Is there a stamp or tag on the alternator that states its amp output? I assume my 5.7's alternator is stock and not high output.

Thanks for any info.

[sunnydude2]

I can answer the guage question. Yes. Xantrex has the link 2000 that does 2 banks, 1000 that does 1 bank. There are others out there, just need to spend the money on one.

Now back to the professionals...:D

[3788sam]

We have the Xantrax 2 bank with the link. The link tells me how many amps it is charging and 2 meters showing battery volts!

[SomeSailor]

Randy;

There are only two things you could measure with a guage (and they're both essentially the same thing). They are Amps and Volts. A voltmeter with a predetermined load resistor would be the best way to go. Install a voltmeter guage somewhere near your switch. Wire an output off each battery to this guage. On the other side of the guage place an inline wire-wound resistor inline on the ground terminal of the guage. This will show you the voltage drop across a known load and indicate a batteries state. The bigger the load the more accurate it'll be. I'd use a momentary switch to supply the voltage to this guage so all you had to do is push the button and see the reading.

Putting the guage inline with your boat would work... but the load will be varying so you'd really never know. A fixed load will show you how much ooomp the battery will have at a given time. A digital guage would be even more accurate.

A battery will only vary from 10.7 to 12.7 VDC so from fully charged, to flat... you'll see those numbers.

[Randygh]

Mike--I have a voltmeter in my boat's dash. I don't know where it is wired but it usually shows 14 volts when I'm running.

It will be easy for me to wire a new meter right next to my battery switches. Let me see if I understand your wiring directions for a voltmeter to check each battery's status. I would run a hot lead from each battery to three momentary switches (one hot wire to one switch) . From each switch I would run a lead to the + terminal on back of the voltmeter. I would run a ground wire in series to a resistor and from the resistor a wire to the - terminal on the voltmeter. How many ohm resistor? When I want to check the charge of the battery I'd push the appropriate monetary switch.

Is this correct? Seems very simple and inexpensive.

[SomeSailor]

Yep... Thats about it. Another way to wire it would be a toggle switch with an "ON-OFF-MOMENTARY ON".

You could then have it:

OFF for normal running.

ON to see charge voltage (like your dash guage)

MOMENTARY ON for testing the voltage under a small load.

It might take some experimentation (resistor size) to get to meter to deflect the amount you want. But, you could easily get it so the meter would not deflect at all at say 11VDC and deflect full right at say 12.7VDC.

The resistor value isn't critical, as you're just applying a momentary load for the voltmeter to feel. Bigger value will increase the voltage sensed. You can find them at your local Radio Shack.

For the price though... you cant beat these guys: LED Battery Capacity Meter (http://www.wholesalesolar.com/meters.html)

I bought a shunt a couple of years ago from them with the intention of installing a remote ammeter downstairs... never did it though. :( Next boat... :)

[Never Again II]

Thanks for all the input. I would love nothing more than to buy a nice sparkling new 2000W/50amp inverter/charger and a few new battery swithces and a nice new genarator & alternators while I'm at it. As soon as money is no issue, I'll begin down that road. For now, I already own the 20 amp charger and 1500W inverter (whose primary job will be running a microwave for a couple minutes at a time). On a combination of advice, I rewired the chargers' outputs to feed the starting batteries with the factory charger and my house bank with the aftermarket one. Should do the job pretty well. On the generator note...we run a 3058 with twin 5.0L Mercs. There's about enough space in the engine compartment for a generator the size of a case of pop and I'd have to pull an engine to get it in there. Not a good boat for a genset unless I want to share flybridg space with it. Again, thanks for the advice. With it and a chat with my charger's tech support line, I think it'll do for a while.