Battery Charging / Battery Voltage

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IntoTheBlue

IntoTheBlue

Senior Member
Joined
Jan 10, 2016
Messages
151
Location
USA
Vessel Name
Into The Blue
Vessel Make
Mainship Pilot 43
I have just changed my house batteries to 3 of the 225 aH Gel Cell batteries, which are charged by a Mastervolt 70/12-3 charger. At my dock, plugged in with the charger in operation at a "Float" charge rate, my battery bank display is indicating 12.35 volts. When running the water pump, with a couple of lights on, the battery bank is indicating around 12.2 volts.

The Mastervolt charger display indicates 13.45 volts being provided to the battery bank under the float charge rate.

I have always assumed that with the charger on, the battery bank should read over 13 volts. Should I be concerned that the charger is not working correctly?
 
You may have some terminal corrosion or a corroded wire somewhere in the system. With a digital multi meter, check voltage starting at the charger and working through the system till you find where the voltage changes.

Ted
 
Do you have the 3 Gel cells banked together or switched independently?

Are you using the chargers 3 separate outputs to each batt'y independently or one to charge the bank?

Some chargers you have to jumper the unused output if all available aren't used - if that's the case may need to check the manual.

Otherwise agree w/ Ted re: tracking to see where you have full V and where it's dropped - definitely sounds like a V drop someplace
 
The battery voltage of 12.2 I would be concerned. Take a voltage reading it the battery with the charger turned off and no, zero draw load. Old school, 12.8 is 100% charged, 12.6 is 75% charged, 12.4 is 50% charged, less than 12.2 probably needs replacing.
 
Last edited:
O C Diver said:
You may have some terminal corrosion or a corroded wire somewhere in the system. With a digital multi meter, check voltage starting at the charger and working through the system till you find where the voltage changes.

Ted
Click to expand...

This is the advice to follow... :)
 
I will be interested once we are on our way to see what the reading is when the alternators kick in.
 
When you say you are reading various voltage levels, where are you getting the readings? Are they analog or digital? Do you trust that gauge? Are you cross checking and getting the same readings on all gauges? at those various levels?
 
The output from the charger is 13.5 v, which I verified with a multimeter. The meter at the helm reads 12.35. I verified this with a multimeter placed on battery 1 of the battery bank.
 
If the batteries are low, why then is the charger in "Float Stage"?
 
IntoTheBlue said:
If the batteries are low, why then is the charger in "Float Stage"?
Click to expand...

Float still has some current flow. There may be some resistance in the wire to the batteries which may account for the voltage difference.

Things to check:
How long is the wire length from the charger to the batteries?
What is the minimum wire gauge in that run?
Does the wire go through a series of splices / junctions between the two?
Is there a fuse in the line?
Any corrosion on the battery terminals?

When following the wires, check both positive and the negative wires.

Ted
 
Ted is sending you in the right direction. You are "losing" Voltage. Poor connection somewhere. If you cannot find it. Break, Clean and reconnect each. Use new hardware if available. Good hand held Volt meter should help you find it. Do not ignore it. Poor connections generate HEAT. In your boat HEAT from electrical high resistance is not desirable. Good luck. . Find it. Love your boat by the way.:thumb:
Dave
 
Thanks. There is a point where the wiring from the charger and the batteries travels through a bulkhead to what I call the "abyss". So basically I can only follow the battery cables to and from the bulkhead. I tried to bypass all by wiring the charger directly to the battery bank. The result is the same.

What's making me a bit crazy is that when I start up the engines, the alternator charges the batteries and they go right up to over 13 v. So charging is OK from the alternators, but not with the chargers?
 
The wires you ran directly from the charger to the batteries, how long are they and what wire size? I'm getting the impression there is a substantial distance between the two. If the charger is easy to move, disconnect it from the wiring and temporarily position it within a couple feet of the batteries. Wire it with short leads to the batteries and plug it in. This will either tell you there is a problem with the current wire run or your charger as the system seems to work fine off the alternator.

Ted
 
If the v drops when you add a small load then it is likely not connected to the charger. Maybe there is a combiner in the mix and at float it is isolating the battery you are testing. Are all three batteries at 12.3 while the charger is putting out 13.4?
 
"Maybe there is a combiner in the mix and at float it is isolating the battery you are testing."

Combiners require the batt voltage to somehow shown to the charger or constant undercharge is the result.

For most boats the RV setup , an $18. buck solenoid does not include these dangers.
 
Well, I caved in and called an electronics guru I know. Went over the phone all of the conditions noted. To which he concluded that I have no problem at all. According to Dan, the Mastervolt Charger I have was going right to float, without producing current because my battery bank was already fully charged. Knowing that the batteries would charge by my alternators, I decided to go on with the trip and hope for the best. Out on day 3 on the anchor, our battery bank dipped below 12 v to 11.99. I turned on the generator to see what would happen and within minutes the battery bank was back up to 12.20 v. I let the generator run until the charger went to float, then shut it down. Batteries maintaining over 12.8 status. When traveling with engines on the battery bank reads over 13.75 v. So far it seems like Dan is correct in that the charger regulates current to the batteries need.
 
IntoTheBlue said:
I will be interested once we are on our way to see what the reading is when the alternators kick in.
Click to expand...

I advise starting engines now with some rpm increase and see what reading you get at batts themselves; also check alternator out put. If same reading at batts as via shore power charger then it seems you have battery problems. Run a load test on batts and see what happens.
 
IntoTheBlue said:
Well, I caved in and called an electronics guru I know. Went over the phone all of the conditions noted. To which he concluded that I have no problem at all. According to Dan, the Mastervolt Charger I have was going right to float, without producing current because my battery bank was already fully charged. Knowing that the batteries would charge by my alternators, I decided to go on with the trip and hope for the best. Out on day 3 on the anchor, our battery bank dipped below 12 v to 11.99. I turned on the generator to see what would happen and within minutes the battery bank was back up to 12.20 v. I let the generator run until the charger went to float, then shut it down. Batteries maintaining over 12.8 status. When traveling with engines on the battery bank reads over 13.75 v. So far it seems like Dan is correct in that the charger regulates current to the batteries need.
Click to expand...

If you turn all 12 volt devices off in the boat and the voltage at the charger doesn't match the voltage at the battery bank when charging, you still have a wiring problem. While this isn't a reason not to complete your trip, the battery bank won't completely charge if the charger can't correctly measure the bank voltage. Also, the charger may be switching bulk to absorbtion and absorbtion to float too early.

Ted
 
O C Diver said:
The wires you ran directly from the charger to the batteries, how long are they and what wire size? I'm getting the impression there is a substantial distance between the two. If the charger is easy to move, disconnect it from the wiring and temporarily position it within a couple feet of the batteries. Wire it with short leads to the batteries and plug it in. This will either tell you there is a problem with the current wire run or your charger as the system seems to work fine off the alternator.

Ted
Click to expand...

Ted, I connected a 3 foot, 3 awg wire from the positive output to a 75 amp fuze and then a 2 foot, 3 awg from the fuze directly to the positive lead on the battery. I left the ground on the charger, which is connected to a ground busbar on the boat.

As there is no problem with alternator charging (as mentioned) and after 3 days on anchor still running about 12 v on the batteries, I don't think that there is a voltage draw somewhere in the dc outlets. So this would have be somewhere between the charger and battery bank. Am I on the right track?

Thanks, Dave
 
SailorGreg said:
Maybe there is a combiner in the mix and at float it is isolating the battery you are testing.?
Click to expand...

FF said:
"Maybe there is a combiner in the mix and at float it is isolating the battery you are testing."

Combiners require the batt voltage to somehow shown to the charger or constant undercharge is the result.

For most boats the RV setup , an $18. buck solenoid does not include these dangers.
Click to expand...

Could be. The old style Combiners can drop 1V or more between the charging Battery and the others in the system...
 
Forget for a minute what the "battery monitor" says and use your DVM to read the voltage directly from the lead posts of the battery with no loads connected except the charger. They should be within 0.1 volts of the charger at float. If the DVM reads lower than the charger indication, you have a wiring problem no if, ands, or buts.
The only other thing would be the charger voltage calibration is sensing higher than actual fooling the charger into float early. You can easily check that by reading the voltage at the charger output terminals and comparing to the charger gauge.
 
Last edited:
As we are in a trip up the northeast, and so far the weather has not been favorable, I really needed to get this corrected. So I came inland to New Bedford, went to West Marine, bought some cable and rewired the entire charging system to the battery bank. Once completed the battery bank immediately started charging, the charger producing current. So we're good to go.
I really thank all for your advice and steerage, for lack of a better term. On this boat you just can't follow the cable from the charger to the battery, as it circles through a bulkhead wall. Your advice convinced me to just re-wire my own system. Thanks again.
 
Heron said:
Could be. The old style Combiners can drop 1V or more between the charging Battery and the others in the system...
Click to expand...

You might be thinking of an isolator which incorporates a diode that can rob about a volt.
 
IntoTheBlue said:
As we are in a trip up the northeast, and so far the weather has not been favorable, I really needed to get this corrected. So I came inland to New Bedford, went to West Marine, bought some cable and rewired the entire charging system to the battery bank. Once completed the battery bank immediately started charging, the charger producing current. So we're good to go.
I really thank all for your advice and steerage, for lack of a better term. On this boat you just can't follow the cable from the charger to the battery, as it circles through a bulkhead wall. Your advice convinced me to just re-wire my own system. Thanks again.
Click to expand...

Glad to hear you resolved the problem. Sorry I wasn't able to answer you yesterday, I was in transit all day.

Ted
 
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