Puzzling Battery Bank Problem

[whaler23]

My 32v system has two sets of 4(8d) batteries. It has what appears to be an original Dresser 40AMP Converter, vintage 1968. Engines are 8V71N's. I went to check on the boat tonight and fired up the stbd engine, fired up fine. The cranking power on the port engine was insufficient to crank it enough to fire, eventually flattening the batteries completely. This is the second time this has happened after long absences from the boat. The air temp in the engine room is around 50, heated for the winter. After the cranking the Dresser immediately threw a charge into the bank at 30+amps. In less than an hour there was plenty of juice to fire the engine which I did. The water levels in all batteries on the weak bank were fine. Is it time to upgrade the Dresser (converter) to a more sophisticated charger? Why is one bank good and the other running to flat over time, the port engine bank is only about a year and a half old. The stbd bank is about the same age.

 

[Sonny]

start with the simple stuff - clean all connections. load test each battery individually. then remove the dresser and replace with a 3 stage charger.

 

[Pascal]

indeed check the connections... i assume this antique charger is a two bank model, make sure both outputs work... only way to be sure is with a multimeter... turn the charger on and see if voltage goes up.

 

[SKYCHENEY]

Loose or corroded connection at the batteries or at that starter. Also could be a bad cell or bad battery in that bank. Get a hydrometer and check each cell.

 

[Brian Degulis]

The puzzling part of this is that the batts are on charge while he's away. Then he comes to the boat and can't crank one egine. Then after charging for an hour or so he can start the dead side. You would think that his charge level would be the highest after sitting for days or weeks not after an hour or so of charging.

Sure check the conections but I'm betting on a bad battery. I would get a hydrometer and check the batts after sitting and charging for a while before any atempt to start. If you see nothing there then try the parrallel switch if you have one or jumper cables (good ones) from the good side to bad. If that does the trick at least then you know it's one or more batts on that side. I would say load test but I've never been able to find an 8V load tester if anybody knows were to get one please let me know.

Good luck

Brian

 

[whaler23]

I'll check each cell on the bank but with regular use the batteries operate fine. It's only after a dormant period do they lose their charge. It seems as if the charger doesn't recognize the drop or only recognizes a significant drop and responds by charging heavily and slowly dropping off. Not sure why this wouldn't be the case with the other bank as well unless as previously mentioned the two bank charger has a bad bank sensor. I'm pricing new chargers this week. I think I'm going to go for a two bank 32v charger and install a separate 12v bank for the electronics. I'll opt for a separate charger just for the 12 volt bank. Right now the bank that constantly goes weak has a tap installed on one of the batteries to give me the 12v I need to run the electronics.

 

[SeaEric]

Scott, How will you charge the intended 12v bank while underway?

 

[whaler23]

The generator is almost always on, otherwise I'd need to find some type of transformer to knock down the 32 to 12, not really what I want to do. Electronics primarily DF, GPS and VHF, occasionally radar.

 

[yachtsmanbill]

I plan to hang a 12 VDC alternator on the starboard main to charge my 12 volt system while underway. ws

 

[rwetherington]

Remember that the stbd batteries are for starting the stbd engine and generator and running the alarm. the port side is for starting the port engine and running the house. The charger is not sensing that the port batteries are down. remember you can parralle the batteries when you crank.

 

[Brian Degulis]

I'll check each cell on the bank but with regular use the batteries operate fine. It's only after a dormant period do they lose their charge. It seems as if the charger doesn't recognize the drop or only recognizes a significant drop and responds by charging heavily and slowly dropping off. Not sure why this wouldn't be the case with the other bank as well unless as previously mentioned the two bank charger has a bad bank sensor. I'm pricing new chargers this week. I think I'm going to go for a two bank 32v charger and install a separate 12v bank for the electronics. I'll opt for a separate charger just for the 12 volt bank. Right now the bank that constantly goes weak has a tap installed on one of the batteries to give me the 12v I need to run the electronics.

That tap could be causing your problem it's a bad idea because when 12V is required only 6 of the cells in the bank are being discharged. That lowers the bank voltage and tells the charger to come on. So your charging the whole bank when all but 6 cells are fully charged. This causes overcharging of some cells and under charging of others.

Adding a 12V battery and charger is OK as long as you have the gen set going to run the charger or a seperate 12v alternator. I would look into a converter like a Newmar DC to DC. That way you don't need the 12V battery alternator and charger in adition it's regulated so your electronics get perfect power no voltage fluctuations from charging and discharging.

Brian

 

[whaler23]

No 12volt electronics are in use when the bank goes flat so I don't think that's the problem. IT's flattening after sitting for extended periods of time.

 

[Nonchalant1]

Check for sensor wires. Some of those old battery chargers only monitor one bank to decide when to run, which is done via a sensor wire to monitor that battery bank state of charge. Then when it runs, it charges both banks and turns off when the monitored bank hits the full charge voltage. If your sensor wire runs to the SB bank, then it only charges the port bank when the SB bank runs low. If the SB bank stays charged, the charger never comes on, so the port bank discharges over time. Then, when you use the SB bank to start an engine, it comes on and charges both banks.

Another possibility is that one or more of your port bank batteries has gone bad or is sulphated up and needs to be equalized. If that happens, it will quickly return a high voltage reading to the charger when it is being charged and the charger will turn off before the bank is actually charged. To check this, you need to get a good hydrometer that reads specific gravity and check every cell in every battery. If the "fully charged" bank has any cells that are low when the other cells are up around 1250, it is bad or needs to be equalized and it won't hold a charge. Equalize the batteries until all cells are equal and around 1250 when charged (at 70 degrees). If a battery won't come up to equalization after 2 days of equalization charging, it's shot.

Doug Shuman

 

[Sonny]

if it is a case of a sulphated battery then equalization won't be possible-he has 8v batteries and that dresser probably doesn't have an equalization feature on it. the only other thing to check is the cut-in voltage on the charger, and this is assuming that the charger sees two separate banks,not a "slave and master" as described above, basically two chargers in one chassis.
all the load testers i've seen work from 6v up to 12v, the different ranges are printed on the card.

 

[Nonchalant1]

if it is a case of a sulphated battery then equalization won't be possible-he has 8v batteries and that dresser probably doesn't have an equalization feature on it.

Respectfully, that's wrong. (Aren't we always respectful here?)

Per the head of battery engineering at Rolls, you can easily equalize one 8 volt battery with a 12 volt manual charger. I have personally done it and it works fine. On a Rolls 8HHG25PM battery and a MANUAL 5 and 10 amp charger set to 5 amps, it took about 36 hours to fully equalize to where every cell read about 1250.

Also, on old chargers that have a sensing wire or connector, you can disconnect the sensor and the charger will run constantly because it's looking for 37 volts (or whatever it's set for) to turn off. You just run the charger constantly until all 4 cells in every battery are up to 1250 specific gravity.

Both of these methods require filling them up properly with distilled water first, keeping them filled reasonably well, watching temps every few hours if you have a powerful charger, and testing the cells as they come up.

Doug Shuman

 

[Brian Degulis]

No 12volt electronics are in use when the bank goes flat so I don't think that's the problem. IT's flattening after sitting for extended periods of time.

I understand what I'm suggesting is that the 12V tap may have caused damage to one or more batteries in that bank.

Brian

 

[GJH]

Brian is absolutely right about that 12v tap. Get rid of it ASAP. That bank won't get properly charged and you may well have damaged the bank as a result, since part is being over charged and part is being under charged. The electronics may not seem to be much of a load, but over time the damage will be done. Your thinking around the fact that this only happens when the boat is left idle for awhile is leading down the wrong path. The electronics may or may not be drawing much at idle/"off" (have you confirmed that?), but the damage is being done nonetheless, mostly when you are underway and the alternators are doing the charging. Your Dresser is unable to maintain the damaged bank.

I had this exact issue when I got the boat, and the PO had tapped a 12 volt circuit off the 24 volt thruster bank. The high end Xantrex XC smart charger couldn't keep the bank maintained, the PO couldn't figure out why one of the 8D's kept having to be replaced, etc. Once we split the 12v over to its own battery and charger, all was well (I had my own learning experience with that, but that's a whole 'nother story).

Several of the other issues that others have pointed up are very valid, and you may have a confluence of those factors (some of which may have the tap as the root cause, or at least the "tipping point").

By the way, get yourself a copy of Nigel Calder's "Boat Owners Mechanical and Electrical Manual". It can walk you through all these issues and much more in very well written detail.