honda 8hp battery charger: disconnect when motor running?

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niku

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Oct 2, 2010
4
ODay 26 Pacific Northwest
I have a Honda 8 HP outboard. It comes with a battery charger. Seems very straightforward to hook it up ... but I am bothered/puzzled by one thing.

With most engine alternators setups, we're constantly warned to never disconnect the battery (eg, turn battery switch of Off) while the engine is running, because that will fry the alternator.

But right now the battery is "disconnected" from the alternator, in that I don't have it hooked up at all. As far as I know there is no switch to "turn on / enable" the alternator. Why has my alternator not already been fried, simply by not yet hooking it up? And when I do have it hooked up, will it be bad for me to turn my battery switch to Off with the motor running?

I am sure there is a simple concept I am missing, thanks in advance for your explanation. The owner's manual doesn't say much about this.
 

bria46

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Jan 15, 2011
286
Oday 272 Waukegan, IL, Sarasota, FL
Re: honda 8hp battery charger: disconnect when motor running

Check your owners manual, your local Honda Dealer/Service Center or Honda Corp.
 

CalebD

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Jun 27, 2006
1,479
Tartan 27' 1967 Nyack, NY
Re: honda 8hp battery charger: disconnect when motor running

Yes, check the Honda manual for sure.

You may or may not have fried diodes in your alternator (I assume that is what you mean by: 'It comes with a battery charger'). Depending on the alternator/charger it may be wired with a third wire that turns the charging on and off depending on the voltage in the line.

Can you hook up the charging circuit to your battery(s)? If so you can use a multimeter tool to measure the voltage coming back from the alternator/charger and if it is close to 14 V it is probably still working. Make sure to measure the battery(s) with the voltmeter first to get a baseline voltage.

Welcome to the wonderful world of boat ownership!

My best.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Re: honda 8hp battery charger: disconnect when motor running

Since the thing is a pull start and does not requrie a battery to operate I would suspect that the alternator has one of those regulator things internally sensing the alternator output and keeping it in check when the user does not connect to a battery.
For the record ALL alternators sense voltage and regulate the voltage so as to maintain a safe voltage. So it is OK to have the battery disconnected as long as the regulator can sense alternator voltage. course you would have a hard time getting an inboard started without connecting it to the battery so we don't see that happen much.
When you switch the battery out of the circuit while the engine is running (not just not ever have it in the circuit) the regulator does it's best to keep the voltage in check but you can (depends on what charging mode and battery SOC.....) get a voltage spike that may (diodes are pretty sturdy) fry your diodes.
I do know that we routinly swapped out batteries while the engine was running when I was an auto mechanic. never fried an alternator doing it either.
 
Mar 2, 2008
406
Cal 25 mk II T-Bird Marina, West Vancouver
Re: honda 8hp battery charger: disconnect when motor running

Most small (< 10HP) manual-start outboards do not use a true alternator but a simple unregulated magneto-style generator that simply consists of one or more flywheel mounted permanent magnets, a charge coil, a diode rectifier and a fuse. They are usually capable of outputting about 40-50 watts or about 4 amps at a nominal 12 volts at maximum motor speed. The output is proportional to the motor speed and they require a battery to control the voltage. This type of charger system will not be damaged by an open circuit but can be damaged by a short circuit if not fused. Think of it as an unregulated trickle charger.

Look in your manual!
 
Jun 17, 2007
402
MacGregor Mac26S Victoria Tx
Re: honda 8hp battery charger: disconnect when motor running

Jalepeno is correct. It's not really an "alternator." It's a generator - puts out DC voltage, not AC. Notice, no rectifier?
 
Sep 26, 2010
808
Macgregor 1993 26S Houston
Re: honda 8hp battery charger: disconnect when motor running

I have the same motor and it's not connected either. I'll be getting around to upgrading my wiring soon, and will be connecting it finally. So I'm wondering, since the current is in the trickle charger range (5 amps), Is there any danger of overcharging?
Typically I charge my batteries up over the week then go out on the weekend.
If I'm out for a few days, I'll want to add some to the batteries.
Since I'm mostly under sail, I don't see an issue, but what if I have a long leg straight up wind and I motor all day?
 
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