Electrical overload??

[ottawamerc]

I have a Sundancer 268 with a 260 in it, it has one battery for the engine start and 2 batteries for house power. 2 weeks ago when I went out in it I noticed that it wasn't charging the batteries so I tested the alternator and sure enough it wasn't putting out any voltage. I had already replaced the voltage regulator on it in the spring and it seemed like it was blown again? I took it to a alternator repair shop and he confirmed that it was blown but also recommended that I should use a 65 Amp alternator since I had 3 batteries instead of the 55 Amp stock alt. Seemed reasonable enough to me so I bought the 65 amp one. Last weekend I used the boat again, I was on the house power all night and in the morning when I started the boat it wasn't long before I was smelling electrical burning and the volt gauge was reading low. I stopped to check and found the alt was really hot so I switched off the house power at the battery switch and just left the engine battery on and the volts came back to 14v and it worked fine? Is it possible that the stock wire that goes from the batt terminal on the alt to the starter is too small now? or is something else causing havoc on my charging system?

 

[tpenfield]

Perhaps, you used a lot of house power during the overnight and if the 2 house batteries are connected in parallel (which they probably are) there may have been initially too much of a current draw from that alternator, trying to re-charge the batteries.

Do you have a battery switch setup where you can connect just one of the house batteries at a time?

 

[ottawamerc]

No as you said the house batteries are wired in parallel with no switch.

 

[Bt Doctur]

If that is the case then use a battery switch 1-BOTH-2 , C is the house feed . This way you can select 1 house battery at a time to recharge and combine both on the hook.

 

[achris]

... Is it possible that the stock wire that goes from the batt terminal on the alt to the starter is too small now?

As soon as I read that you put a larger alternator in, I wondered if you upgraded the wiring to cope with the higher current. 'nough said.

Chris..........

 

[bruceb58]

As soon as I read that you put a larger alternator in, I wondered if you upgraded the wiring to cope with the higher current. 'nough said.

Chris..........

He went from 55 to 65. Not enough to make a difference.

Personally, I would be putting a lot bigger alternator on there and upgrading the wiring.

 

[bruceb58]

was on the house power all night and in the morning when I started the boat it wasn't long before I was smelling electrical burning and the volt gauge was reading low.

Out of curiosity, how low are you letting your house batteries get? You shouldn't run them lower than 12.0V which is 50% discharge.

 

[achris]

He went from 55 to 65. Not enough to make a difference.

Personally, I would be putting a lot bigger alternator on there and upgrading the wiring.

If the wiring is old and a bit corroded, and the old alternator was tired and not putting out its full output, could have made the difference. If he smelt burning, a connection is getting way too hot. Bigger (new) wires and terminals should fix it.

Chris...

 

[ottawamerc]

Thanks for the input guys, What size of wire would you recommend? #4 or #2?

 

[achris]

65A DC at 12 volt, look for at least 10mm2. Even #6AWG would be adequate. Make sure the lugs you use on the ends are up to the job too. SS is best, copper next, never steel.

 

[bruceb58]

Your boat probably has 10 gauge which means you would only have 0.65V drop @65A if the wire was 5 feet long. You would never have a problem with the wire burning or getting hot with 10 gauge. If you go to 8 gauge you would have a 0.4V drop. 6 gauge would be a 0.25V drop.

Just as a matter of reference, a lot of people use diode isolators that have 0.7V drops so if you were using a 10 gauge wire straight to a battery, you are really no different.

If you go to a 100A alternator, I would go to at least 8 gauge.

You want to use both copper lugs and copper wire that is tinned.

 

[hemi rt]

I'd also check the house batteries for a problem like a shorted cell.