bf 100 charging voltage and rectifier testing

I was hoping to use the charging plug on my old 1985 bf100.. When I checked the voltage it was like 5-6 volts, not wide open but certainly above idle... I would expect amperage to drop with rpm but voltage to remain somewhat constant..or am I all wet??

Anyone with a bf100 charging system tell me what voltage they get.. I wanted to charge the battery with the trollling motor and hook up an electric downrigger as most of my time on the water is spent running the kicker but don't want a dead battery when its time to run back to the launch.. As an aside, what happens to a 12v battery when it gets below voltage charging input?

I don't understand the chart on page 4-25 of the shop manual.. It shows units as K ohm.. Range blue to red 1-200, green to blue 100-50.. Usually ranges are expressed consistently,, like low to high.. This reads low to high in one column and high to low in others...?? Seems like a misprint somewhere..

First off, I'm not an expert on these charging systems....never really utilized them before. I've looked at that chart a few times and it has me confused too. I even wonder if it has something to do with the fact that they list two different meters...the Sanwa and/or the Kowa. They show two different range settings for the differing meters so I had just assumed that was what the two different values listed were about.

Since there are four separate connectors for this system PLUS a fuse and fuse holder, you COULD be experiencing a voltage drop across one or more of any of those connections. I would unplug everything....clean and swab the pins and sockets as well as the fuse ends and it's holder as best as you can and then reconnect and try again.

And, since the AC coil output will be dependent on RPM, I would test it at full throttle because that will be when the most voltage is generated.

If, after doing all that you still only get around "half" volts for charging, I would say that one leg of the rectifier has lost a diode and just dispense with figuring out their chart.

On the other hand, I might try to come up with a better explanation after a good nights sleep and some coffee.

Good luck.

Sorry it took so long but getting to your other question; "what happens to a 12 volt battery when it gets below voltage charging input?"

I would say nothing. Nothing positive and nothing detrimental.

Voltage can be seen as "pressure". Since the battery is holding 12 volts (actually 12.6 v) "pressure", the 5 or 6 or 7 volts your system is trying to introduce is a lesser pressure and, therefore, amps will not flow TO the battery.

The higher "pressure" from the battery also cannot "overcome" the lower pressure and flow "backwards" so to speak to ground because the bridge rectifier acts as a one way valve or gate preventing flow. That's why you can leave the battery charge connection hooked up with the engine off and the battery won't be drained.

UNLESS, one of the diodes that make up the rectifier is shorted or has lost "reverse bias". In which case current COULD be allowed to flow and seek ground through the faulty diode. It would need to travel through the charge coil to do so and, hopefully, the fuse would blow before the coil windings overheated due to over-current. That's why we never want to replace that fuse with one of a higher amperage rating.