16 volts with silenium rectifier - too much?

[GG]

Hello all,

I had to change my battery, I replaced it with another gel battery, and tested the voltage after installation. With the lights off, I get a full 14 volts. With the lights on and accelerating the motor, the voltage at the battery goes as high as 16 volts! I never had that before. And with the switch in the "middle" (for charging), it might go even higher - up to 17 volts at higher rpm's

I have the old silenium rectifier. Do these voltage reading means it is shot? I used to have low voltage - was hard keeping the battery charged! Any ideas? Maybe a bad rectifier fried my former battery?

Thanks!

GG

[sky.fred]

A rectifier only transforms AC into DC, it does not regulate.
A regulator in good working order must not exceed 15 V, otherwise the battery may overheat.
I don't know what kind of bike you have but Older Hondas don't have regulators, but often two charging circuits, one for “day” and one for “night”. The night circuit is added to the day circuit, and the bulbs absorb the extra volts.
This is not a very reliable system, and it's better to modify it and fit a modern regulator rectifier, which is what I did on my C72.

viewtopic.php?f=22&t=7643370&start=49

[Tim Allman]

Here's a link to the CB77 Shop Manual.

https://drive.google.com/file/d/1eQNecw ... sp=sharing

On page 153 is a graph relating the charging voltage and current to engine speed. Note that they have reflected the curves at low RPM. The voltage and current become negative below about 1500 RPM indicating discharge.

You'll see that the voltage gets a bit wild because the only regulator is the battery although the limited output of the generator plays a role too. Yes, the battery can overheat and that's what happened with the first model so the magnets in the rotor were weakened in subsequent production.

So, your rectifier seems to be doing what it should. Even though 16 or 17 V is not very good for the battery, you have to live with it. Or, you could install a new rectifier-regulator. The new ones use silicon, not selenium, as the semiconductor. The losses in the rectifier are much less with Si and you should get better charging without cooking the battery.

[GG]

Thanks guys! I didn't mention that the bike was a 1966 Superhawk, with just the silenium rectifier.

My voltage "before" these problems was always in the ballpark, and with an LED taillight I could use the electric start most of the time, and the voltage output to the battery would be a high of 14v. I've never had 16 - and right now, even with the headlight on it continues to climb up to 17v !!!

I'd like to put a regulator / rectifier in, but it looks complicated. And some of the documents aren't available anymore.

Question - what would cause the rectifier to 'allow' so much voltage through it? I've got the 'low' output stator, and before the maximum output was 14v.

Thanks again guys!

GG

[GG]

Thank Tim for the Shop Manual! I only had a Clymer manual. :-)

GG

[Tim Allman]

Question - what would cause the rectifier to 'allow' so much voltage through it? I've got the 'low' output stator, and before the maximum output was 14v.
GG

The rectifier does nothing but convert the AC that the generator produces to DC. It does no regulation at all. Without the battery the output looks like a line of camels, going alternately from 0 V to whatever the generator can produce. It's the battery that "regulates" the voltage because it will provide voltage while the rectifier output is low and absorb the peaks when it is high. When you measure the voltage with your voltmeter you are getting an average value. It may be that the poor condition of your old battery kept the voltage lower but if you look at the graph I mentioned you can see that 17V is what the designer of the electrical system wanted.

This system really just represents common practice when these bikes were designed, probably in 1959 or 1960. That said, British bikes had Zener diodes which clipped off the peaks and provided some regulation. Honda could (should?) have used them but didn't.

[GG]

Yep, I see the graph. Strange my battery has actually lasted as long as it has! I'm often at 5,000 to 6,000 rpm's - some long trips. I can't imagine the battery taking that sort of beating! Wow.

Looks like I'm going to look how to install a regulator / rectifier - I'm planning on keep the bike!!

Thanks very much!
GG