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Generator overcharging after switch to 8 volts?

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scottz
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Generator overcharging after switch to 8 volts?

Post by scottz » Thu Aug 01, 2013 2:39 pm

I've got a '56 Sportsman that's been very hard to start. I'm new to this, and on the advice of friends, switched to an 8 volt battery. The boat now starts and runs wonderfully, but the ammeter quickly pegs at 20 amps at anything over 1,000 rpm (estimated - a new tach cable is on the to-do list). Even with the lousy old 6 volt battery, I've not seen this before.

Any ideas what's going on? I don't want to cook a new, and rather expensive, new battery.

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mfine
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Re: Generator overcharging after switch to 8 volts?

Post by mfine » Fri Aug 02, 2013 6:34 am

Was the battery fully charged before you put it in? It could take a while to get the battery to full if it wasn't.

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mbigpops
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Re: Generator overcharging after switch to 8 volts?

Post by mbigpops » Fri Aug 02, 2013 8:17 am

I have not gotten to gauges yet but if your type may be designed specifically for 6 volts and not read correctly with your new 8 volt setup.

You may want to contact one of the recommended gauge restorers and ask the question.

Mark
1953 CC Rocket Runabout "Rocket Man"

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Re: Generator overcharging after switch to 8 volts?

Post by sproat3 » Mon Aug 05, 2013 12:42 am

Scottz-

Your ammeter is probably right. You didn't say if you replaced your alternator or voltage regulator, but you probably didn't as I don;t know where you would find 8V generator and regulator.
The most logical explanation is that you are now trying to charge an 8V battery with 6 volts. Depending on the ampere hour rating of the 8V battery, it will take more current at a lower (6V) voltage to get it fully charged. The ammeter reads current, not voltage so it is probably correct. If it is pegging at 20 amps, it is probably drawing more than that and could be overloading the wires. #12AWG wire is rated for 20 amps continuous. If your charging circuit is less than #12, check the fusing of the circuit. Hot wires and no/too large fuses are a fire waiting to happen.
Suggest you have a qualified marine electrician check this out. Much cheaper than the alternatives.
Ward
1960 Chris Craft Capri (Tahoe Heidi)

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Re: Generator overcharging after switch to 8 volts?

Post by jfrprops » Mon Aug 05, 2013 10:06 pm

there have been good post on this in the archive, check it out.

John in Va.
1980 Fairchild Scout 30
19?? custom Argentine Runabout 16'
1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

scottz
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Re: Generator overcharging after switch to 8 volts?

Post by scottz » Mon Aug 12, 2013 10:23 am

Thanks, everyone, for the advice. The boat's out of service now until I can find a qualified marine electrician, as I suspect sprout 3 is probably right. It's interesting to me that, with all that I've been told and seen written about this "conversion" that this particular issue has not come up.

Any leads on a qualified marine electrician anywhere close to Madison, Wisconsin?

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evansjw44
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Re: Generator overcharging after switch to 8 volts?

Post by evansjw44 » Mon Aug 12, 2013 7:27 pm

You are more in need of a good mechanic with electrical skills. But my take would be that the cut-out is not working. The cut-out disconnects the generator from the battery when when the generator voltage falls off at low speed and the battery tries to run the generator as a motor. That's right, a generator will "motor" if the battery voltge is higher than the generator voltage. The cut-out is in the voltage regulator. If you have an old "third brush" generator, then all you have is a cut-out and its usually mounted on the generator where as a voltage regulator is mounted off the engine and has three or four wiresand has a field voltage relay as well as a cut-out.. What the cut-out does is connect the generator to the battery when the generator voltage is higher than the battery voltage and disconnects it when the generator tries to accept current from the battery and run like a motor. The contact on the cut-out can "weld" so that it stays closed when it should open. If the generator tries to "motor" it will draw high currents and will usually show as Discharge" on an ammeter if the ammeter is wired correctly.
Jim Evans

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Re: Generator overcharging after switch to 8 volts?

Post by jfrprops » Mon Aug 12, 2013 9:19 pm

Good explanation by Jim......and those things can and do "weld" exactly as he says....

John in Va.
1980 Fairchild Scout 30
19?? custom Argentine Runabout 16'
1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

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evansjw44
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Re: Generator overcharging after switch to 8 volts?

Post by evansjw44 » Wed Aug 14, 2013 6:14 pm

Addendum: If you have a regulator/cut-out set up for a 6 volt battery here's how it works. As the engine turns and the generator picks up voltage (generator voltage is directly proportional to engine revs) the cut-out will connect the generator to the battery at approximately 6.8 volts (at the generator terminal, disconnected). Once connected it will try to regulate to 6,8 - 7.0 volts to charge a 6 volt battery. But if connected to an 8 volt battery it will connect to the battery at 6.8 volts (lower than the 8.6 {at rest voltage of an 8 volt- 4 cell lead acid battery} an immediately try to "motor". Current flow will be towards the generator instead of towards the battery and will be significantly higher than expected. The cut-out should sense current going in the wrong direction and try to disconnect but the generator output voltage will try to connect and there will be a conflict. Eventually the cut-out/regulator contact will arc and "weld".

If you want to use an 8 volt battery the voltage regulator must be "tuned" to work with the higher voltage battery.
Jim Evans

jfrprops
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Re: Generator overcharging after switch to 8 volts?

Post by jfrprops » Wed Aug 14, 2013 9:54 pm

Now Gang, you can't find this kind of in depth IMPORTANT advice just anywhere.....that is the true value of this great site!

John in Va.
1980 Fairchild Scout 30
19?? custom Argentine Runabout 16'
1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

Tom Gruenauer
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Re: Generator overcharging after switch to 8 volts?

Post by Tom Gruenauer » Thu Aug 15, 2013 8:18 am

Jim,
Great job!! One other question.
Do you adjust the third brush in the generator to get the 6.8-7.0 volts? Where would you place your hand held volt meter with the engine running? Amps? What did you mean Disconnected?
Tom

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evansjw44
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Re: Generator overcharging after switch to 8 volts?

Post by evansjw44 » Thu Aug 15, 2013 9:45 am

Third Brush. That's a kind of empirical setting. The objective is to get the ammeter into the charge zone at some reasonable revs. I'd try for 1200 but that just pulling numbers out of thin air. You could put your voltmeter on the battery terminals and you should see the battery voltage come up when the cut-out closes and I'd be happy with 6.8 7.0 volts. The trade off is that at higher revs you might be over-charging the battery and you'll use a lot of water and sulfatee the plates. If you run a lot at 2500 reves then set the third brush so the charging is not too high at higher revs. It's kind of primitive thing.

Old cars (circa 1930) had third brush generators. If you were going on a long trip you would turn on the headlights to lower the charging of the battery.
Jim Evans

Tom Gruenauer
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Re: Generator overcharging after switch to 8 volts?

Post by Tom Gruenauer » Fri Aug 16, 2013 8:06 am

Thanks for your help Jim, I'm putting together a Chrysler Imperial LM-C 6 cyl. from 1928. There is not much info on this kind of stuff out there.
Tom

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evansjw44
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Re: Generator overcharging after switch to 8 volts?

Post by evansjw44 » Fri Aug 16, 2013 10:49 am

I built up a 1947 Chrysler ACE for my brother a could of years ago. The Chrysler is a bit odd compared to the CC Herc and the Gray Contientals.
Jim Evans

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drrot
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Re: Generator overcharging after switch to 8 volts?

Post by drrot » Fri Aug 16, 2013 12:46 pm

The Chrysler LM uses Delco And is a bit different
Jim Staib
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1947 Penn Yan 12' Cartopper WXH474611
1950 Chris-Craft 22' Sportsman U-22-1532
1957 Chris-Craft 26' Sea Skiff SK-26-515
1968 Century 17' Resorter FG-68-174

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