My new (to me) boat came with a 1995 Honda outboard BF25. The other day I noticed that the voltage at the battery with the engine running at WOT was somewhere close to 16V, I though the voltmeter went nuts and double checked with a tester and to my surprise it was reading 15.8v. I have two group 24 batteries and only one was connected at that time so I connected the two batteries and the voltage went down for a couple of minutes and back again to 15.6v. The batteries where not hot nor gurgling, but just in case I started turbing on lights until the voltage droped to the low 14s. After that I checked the engine's manuals and saw that it only has a rectifier and not a volt. regulator for the 6amp charger. Dow you think I'll burn the batteries if I don't control the voltage? What are my options for controlling the voltage? Thanks
Unregulated Outboard battery charger
- Thread starter MafaldaII
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Rectifiers
Honda has used that exact same system since the 1970's. Every Honda motorcycle of that era used this system. I would suspect that the rectifier has a bad diode in it, allowing excess voltage through. The rectifiers can so some spooky things when they have a bad ground or a burned out diode, or an internal short. I would check first to make sure this is not within the limits it is set for, but would strongly suspect the rectifier is bad, or has a bad ground. The output specs should be in the manual.
Honda has used that exact same system since the 1970's. Every Honda motorcycle of that era used this system. I would suspect that the rectifier has a bad diode in it, allowing excess voltage through. The rectifiers can so some spooky things when they have a bad ground or a burned out diode, or an internal short. I would check first to make sure this is not within the limits it is set for, but would strongly suspect the rectifier is bad, or has a bad ground. The output specs should be in the manual.
That outboard does'nt have enough oomph to damage a big battery in any reasonable amount of time, or I would guess, to drive the voltage at the Battery Terminals to 16 volts. The output is more like a constant current source and if the wire between where you were measuring and the battery is undersized then you would get a high voltage.
I suggest that you measure again, right on the battery terminals. If you still get that high a voltage I would have to believe the batteries are on the way out.
I got 11 years out of a single deep cycle battery hooked up to a Honda BF100 outboard. Just kept the level up.
I suggest that you measure again, right on the battery terminals. If you still get that high a voltage I would have to believe the batteries are on the way out.
I got 11 years out of a single deep cycle battery hooked up to a Honda BF100 outboard. Just kept the level up.
Even our lil 5 HP Suzuki outboard has a "charging" coil on it. As pointed out, these are not regulated. For larger engines, it's obviously intended to charge the starter battery; for small pull-start engines like ours, the charging coil is there to top up a boat battery, or to run nav lights.
The service manual for our outboard mentions that the output is unregulated, and for that reason it recommends that the charging output only be used for charging the basic flooded-cell lead-acid battery, not sealed or AGM types.
malfadall, what kind of boat do you have?
A sustained 16v measured at the battery is not a good thing; eventually the batteries will boil and outgas. Basic flooded-cell batteries will tolerate this better than sealed or AGM.
A friend of mine put a switchable power resistor in series with the charging coil of his outboard so that when the batteries are nearly full-up, switching in the resistor drops the current to a safe "top-off" value.
The service manual for our outboard mentions that the output is unregulated, and for that reason it recommends that the charging output only be used for charging the basic flooded-cell lead-acid battery, not sealed or AGM types.
malfadall, what kind of boat do you have?
A sustained 16v measured at the battery is not a good thing; eventually the batteries will boil and outgas. Basic flooded-cell batteries will tolerate this better than sealed or AGM.
A friend of mine put a switchable power resistor in series with the charging coil of his outboard so that when the batteries are nearly full-up, switching in the resistor drops the current to a safe "top-off" value.
Kenn;
My new to me boat is a Gemini 3200. I guess what your friend is doing with the switchable power resitor is similar to what I'm doing turning enough lights on to drop the voltage. I saw that the newer versions of this outboard comes with a regulator, I wonder if it could be adapted to mine...
Johnb;
I tested the voltage at the battery terminals and I doubt the batteries are bad, they are less than a year old. I think the problem is that the batteries are always fully charged when I start the outboard.
Thanks for your replys
My new to me boat is a Gemini 3200. I guess what your friend is doing with the switchable power resitor is similar to what I'm doing turning enough lights on to drop the voltage. I saw that the newer versions of this outboard comes with a regulator, I wonder if it could be adapted to mine...
Johnb;
I tested the voltage at the battery terminals and I doubt the batteries are bad, they are less than a year old. I think the problem is that the batteries are always fully charged when I start the outboard.
Thanks for your replys
By adding a series resistance, my friend is limiting the voltage and current available to the battery. The load to the outboard's generator goes down.
What you're doing by turning on the lights is drawing out more current from the outboard charger, increasing internal losses that cause the voltage measured at the battery to drop. In other words, you're slightly overloading the outboard's generator, which probably isn't a great idea.
Depending on the max current and voltage available from your outboard's charging circuit, an external regulator might be useful. Or even something that disconnects the charger when the voltage at the battery is higher than a preset value, eg 15 v?
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