is a 55 amp alternator enough to charge 3 group 27 batteries?

[lime4x4]

Lately here i've been finding that my house batteries are going dead rather quickly. There 3 27 group deep cycle batteries.With min load there going dead in about 4 hours. The batteries aren't even a year old.besides the 3 house batteries i also have a marine starting battery. Even if i let the engine run for an hour the house batteries are going dead. I checked the draw on the house banks and it's at 6 amps on the high end and 2 amps on the low end when anchored. I'm starting to think the 55 amp alternator just ain't charging the batteries enough. While running my volt gauge is showing 13.5 volts.

 

[bruceb58]

Re: is a 55 amp alternator enough to charge 3 group 27 batteries?

Explain your setup a little. How do you have all of your batteries hooked together?

 

[fishrdan]

Re: is a 55 amp alternator enough to charge 3 group 27 batteries?

We need more information and I'm shooting in the dark, but here it goes...

Are the batteries completely charged before you go out? If so, they should be lasting a whole lot longer than 4 hours. Even 1 of the group 27's should be lasting at least 4 hours at a 6 amp load, probably more like 8-10.

Have you checked the batteries? If 1 of your batteries is marginal/dead it will discharge the others if they are connected in 1 bank, all wired in parallel. I'd charge the batteries individually and have them tested, testing them with a hydrometer will give you an indication of their condition and you can do this at home with the batteries in the boat. Also check their water level, I have to add some each year to keep them topped off.

How long and at what RPM are you running the engine? The 55amp alt will charge all of the batteries eventually, but it depends on how long you are running the engine, at what RPM and how discharged the batteries are. I can see that they are not getting charged if you are not running the engine at high RPM for a long time. A 55 amp alt will put out 55 amps max, less the loads on it has (engine, lights, accessories) so I would guess it's probably putting out 30 amps at cruise (maybe less). 10 amps/battery for 1 hour isn't much.

If this has been going on for a long time you could have battery issues as leaving a battery partially discharged is bad, can lead to short battery life.

- What gauge wiring is connecting the batteries to the engine, battery cable or wire.
- All connections clean and tight?
- Battery switch(es) being used?
- Battery isolator?
- Onboard charger?

I had a 100 amp alternator on my old boat with 3 house batteries and it would keep them charged. Even if I was hard on the trolling motor or fishing lights they would charge up since I was running the boat 2-3 hours/day. The only time I had a problem running the batteries down was when I was using a lot of power and making a short run back to the marina, many times the batteries were charged up when I got back home and plugged in the charger.

 

[lime4x4]

Re: is a 55 amp alternator enough to charge 3 group 27 batteries?

Batteries were tested and there good.I fully charged them at home and the first day out they worked well. 7 hours on the hook and they didn't die.Second day out they lasted 5 hours then the 3rd day out they lasted 3 hours.I use a battery switch for 2 banks.bank 1 has the starting battery and bank 2 has the 3 house batteries. The starter is wired to the battery switch. When running i have the switch set to all and when anchored i move the switch to bank 2 to just use the house batteries. I ran the engine at 1500 rpm's for about 15 min before heading back to the dock. Then the rpm's vary 2600 to 3800 rpm's. I ordered a new one wire 105 amp alternator which should be here in a day or so. The alternator charging wire is hooked up to the starter which then feeds into the battery switch.

 

[fishrdan]

Re: is a 55 amp alternator enough to charge 3 group 27 batteries?

Up grade you alternator + wire when you install the 105 amp alternator, you are going to be pushing a lot more current down that wire. Can't remember what I used, something like #4 or #6, it was a lot thicker than the stock wire.

 

[bruceb58]

Re: is a 55 amp alternator enough to charge 3 group 27 batteries?

How far are you letting your batteries get down to? You shouldn't let your house battery bank get down below 12.0V which is around the 50% point. This is the problem with using 3 batteries in parallel. One bad cell in one of the 3 batteries is going to drop down the other 2. You are WAY better off having two large 6V batteries than 2 or 3 12V in parallel.

Next time out, monitor the voltage while you are discharging and when you get back after driving the boat. Fully charged at rest will be around 12.7V

By the way, even if you have a 55A alternator, it doesn't mean you are going to be putting out a constant 55A...it will taper off as the batteries charge. So...if you are drawing 7 amps for 4 hours on the hook, you won't necessarily replace the entire charge in an hours time running the engine. Also, charging the battery at...let's say 10A for an hour...does not mean you replaced 10Ahour of capacity to the battery. There are losses due to heat and chemical reactions that require up to 150% charge to replace 100% of battery draw.