Charging problem???

[Scott21120]

Recently I upgraded our house batteries to 2) 6v batteries with 245 ah capacity, in addition to my group 27 starting battery with 105 ah. We are on a mooring, so we get limited engine run time, and limited shore power to run the charger. Our boat had the original 1983 shore power charger, and when the house battery died halfway through the season ( it had tested good a few weeks earlier) I suspected a problem with the charger - it had been acting somewhat erratic earlier. I am in the process of installing a new Trucharge 20, but this weekend we motorsailed for about 4 hours on our way back from a trip. Even with 4 hours of engine run time, the batteries were not charged sufficiently. I pulled the alternator and had it rebuilt - the diodes were shot. Upon reinstalling the alternator, I am still only getting 12.4 volts at the batteries (same as before the rebuild), even though I have 13.7 at the output of the alternator. I am not sure what would cause such a voltage drop - any ideas where to start looking? The alternator is the stock 55 amp Motorola.Thanks,Scott

 

[Mick]

Charging Problem

What type of regulator does this alternator use? Usually the 'stock' alternator has a built in regulator that performs the same as an automotive regulator which doesn't allow enough output to adequately charge a large deep cycle bank. The ouput is enough to recharge the starting battery, and run the loads (instruments etc.) with very little left to charge the house bank correctly.Leaving batteries undercharged leads to sulfation which reduces the capacity of the battery.

 

[Bill Ogilvie]

Voltage drop

I may be wading in over my head here but you could check your alternator ground connection and also the + lead going to the battery. Somewhere between the alternator and the battery you are dropping 1.3 V. That's a lot of voltage drop and should be easy to find with your voltmeter.

 

[Benny]

Good responses.

Your numbers appear to be in the ball park so I would suspect your voltage drop may be in the wiring and connections. Check for high impedance in the wiring and dirty, corroded or loose connections. Do you you have an isolator in the circuit? When these fail they cause a voltage drop. Your batteries may benefit from "Equalization" as they are probably a little sulfated from not being fully charged over a period of time. Some guys are replacing the regulators on older boats with 14.4 Volt ones and claim they can charge their batteries in 1/2 the time without harming them. I looked into it and found it was indeed safe but with the recommendation that the acid level be maintained by periodically adding water. Good luck and let us know what was the cause of the problem once identified.

 

[Mick]

Alternator

13.7 volts is not much more than a float voltage, and is not going to provide a deep charge without running the engine for 24 hours. Nigel Calder gives a good description in his book on boat systems.

 

[Ross]

Lead -acid cells run 2.1 volts per cell

anything more than that is charging the battery. Not very fast but still charging, If the battery is down to 11.5 volts then 13.7 is going to most certainly add to the battery for the next time you place a demand upon it. Consider this you drive your car for five years and give no thought to the battery until one cold morning the car won't start. What is so different with a boat?

 

[Stu Jackson]

Voltage Drop

ScottThe drop is in the wiring, most likely the connections. Check them out carefully. I recently pulled an old battery connector and the wire pulled right out of the lug!Also, your Truecharge 20 will give your banks the proper three stage charge. Your alternator, stock 55A with internal regulation, will not. Consider external regulation and a newer higher output alternator. With an M25 engine (what do you have?) you should stick to 100 amps or less.Stu

 

[Bill Roosa]

Concur with Mick

An automotive regulator is not going to give you anything but a trickle charge as it is not designed to operate on a system where the batteries are the primary source (time wise) of electrical power. Since a car engine is running all the time and the only thing you use the battery for is a short shot to the starter the alternator is designed to just keep the voltage at 12.4ish level to MAINTAIN the batteries in a charged state. They never really get discharged like deep cycles on a boat. The boat manufactures know this but most design for a weekend out then 5 days on the charger scenerio. Being on a mooring you might want to think about solar or wind charging to supplement the charger. The good news is you will never overcharge your batteries while running the engine.

 

[Landsend]

Do you have a battery isolator?

This will cause the large voltage drop. Also check for bad connections. I'd go a new high output alternator and external voltage regulator.

 

[Scott21120]

Thanks for the ideas -

I finished my Truecharge 20 installation, and the batteries are getting a proper charge right now. The alternator is stock - Motorola 55 amp with stock regulator ( as spec'd in 1983). I asked the alternator shop about upgrading to a higher output alternator, but he felt that staying with the 55A for our use was better because it will charge at idle and low rpm where a 100A would not put out at low rpm. I do not have an isolator or combiner at this point, but I have started going through my connections - replacing terminals and cleaning as I go. Once I have made my way through the whole circuit, I'll report on any change.