1975 85hp Johnson charging oddities.

[boxchevyman]

1975 85hp Johnson.
Model: 85ESL75E

Put a generic full bridge rectifier on, wired it up correctly, and checked voltage at battery.

not running= 12.68volts
running= 3.5-12.80 volts
then when I stop the motor after a few minutes the battery shows 12.73 volts

So the net result is the battery charged somewhat. This is very odd to me so I thought I would ask you guys. Also I did an OHM test on the stator.

No wires show continuance to ground on the high scale.
I get 2.3 ohms resistance between the yellows on the low scale.

This was on a cheep harbor freight digital MM.

So what do you think?
Thanks,
James

 

[boobie]

At what rpm did you run the motor at and for how long ??

 

[F_R]

Yeah, it takes awhile for enough juice to flow into the battery to make a significant voltage increase---especially if it is not fully charged to begin with. Your "some" increase indicates it is working, but hasn't had enough time. But discard all this if it was already fully charged and ran awhile.

 

[boxchevyman]

I ran it on muffs out of gear on low rpm and then as high as the warm up lever would let me go for about 1-2 minutes. One interesting thing was the MM aperred like it was showing lower voltage more often like 3-8 volts at higher rpm, while on low idle it would show 12.76 or so for a few seconds then low voltage then back up for a few secconds then repeat. this is weird. I'm not sure what this means or where i should look.

Does this sound like a rectifier problem? I took it off and retested it after i ran it and it was good. battery leads are connected right. My cheap analog meter shows a constant DC voltage but that may be because it doesn't have a high sampling rate.

the battery is a brand new group 29 ( the bigger one) marine battery just bought a month ago. the battery has maybe two trips on it.

I don't know if this helps you guys at all.
thanks,
James

 

[emdsapmgr]

That older engine charges through the rectifier. (it's not regulated like the newer combination rectifier/regulators.) It's typical on those that the volt meter will show normal battery voltage after just starting. Once the engine runs for 5-10 minutes, the voltage will increase. After 20 minutes, it's very typical to see 16+ volts at the battery. That's normal. Yours is not. Make sure you are using a marine starting battery. A deep cycle will work, but the constant charging of it will reduce it's life span. If it had the later combination rectifier/regulator it would charge up to around 13.5 volts after 20 minutes.

 

[boxchevyman]

Ok I understand this is weird. I guess my question is at this point do you think there is any harm in running the motor this way? Do you guys think it wil fry my stator?

Thanks,
James

 

[emdsapmgr]

The stator has two sets of coils. Some charge the battery, others provide ignition voltage. Separate coil systems. Having said that, I'm just not sure what effect your rectifier will have on the charging side of the system long term. In the late 50's many engines had electric start and no charging system. My 57 50 hp was one. That battery was just there to crank the starter. The engine made it's own voltage after starting. So there was no battery drain when running. It would go for months before I'd recharge the battery. Your 85 also make it's own voltage to fire the ignition. If you have power trim or run a fishfinder or bilge pump, run the lights, horn (none of the accessories I ever had) those draw on the battery and it may not last that long before you need to recharge.