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#438232 - 06/04/12 2:57 am First Run Squawks - Voltage  
Joined: Aug 2010
Posts: 205
DaveOfTexas Offline
BritBike Forum member
DaveOfTexas  Offline
BritBike Forum member

Joined: Aug 2010
Posts: 205
Texas USA
Zener diode, new 12V 9aH flooded cell battery fully charged, no lights etc on. Only draw is the electronic ignition.
The voltage across the battery terminals reads 15v when it is running at a fast idle (see video in By Gawd thread).

That will surely boil the battery.
How to tone it down?? Needs to be 13.8-14.2V ime.


1969 BSA B44VS PC8113
Engine PC8113B44VS
Recently acquired (Feb 2011) Aiming to get running and return all parts/configurations to original.
First BSA. Have 1970 Honda CB750 too.
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#438243 - 06/04/12 4:22 am Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Aug 2001
Posts: 1,799
Kevin (NZ). Offline
BritBike Forum member
Kevin (NZ).  Offline
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Joined: Aug 2001
Posts: 1,799
Christchurch, NZ
The Zener diode controls the voltage. What did the voltage drop to with the lights turned on. How about readings at low rpm and then again with a good rev..

I would be thinking the meter, - is it reading correctly?
There will still be a little ac ripple but you are measuring at the correct place, - across the battery itself.

Next would be checking the Zener earth. Are there any floating voltages in the system ? ie some components not earthed correctly or linked to a common ground point.
Is the Zener indeed connected to the rectifier output and battery live correctly.

It may be a fauly Zener, you could put the meter over that and see if you get similar results. The voltage should obviously plateau at the Zener operating voltage.

At least you have too much charge. Easier to fix than too little.
To prevent boiling the battery you could run with the lights on... or even pulling an alternator ac lead off the input to the rectifier.

It shouldn't be too difficult to work through and fix this one.

Last edited by Kevin (NZ).; 06/05/12 12:26 am. Reason: shouldn't

Why, Y, Dash Y..



#438274 - 06/04/12 10:04 am Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Jun 2002
Posts: 9,292
Stuart Online content
BritBike Forum member
Stuart  Online Content
BritBike Forum member

Joined: Jun 2002
Posts: 9,292
Scotland
Hi Dave,

Originally Posted By: DaveOfTexas
The voltage across the battery terminals reads 15v

Agree with Kevin.

1. Have you tried a known good battery in your multimeter? As I found out just yesterday, even when measuring Volts, my multimeter's reading was high due to a failing internal battery. frown Or try just another multimeter.

2. Do you always have battery Volts at the Zener's tab terminal?

3. Have you checked for any resistance between the Zener's stud and battery +ve?

However, as long as the Volts don't go higher than 15V, you might be stuck with that limit unless you change the Zener; that's what many new ones have been working to for some years. And, if you change the Zener, there isn't any guarantee that another one won't regulate until a similar Voltage. frown

Originally Posted By: DaveOfTexas
That will surely boil the battery.

Ime, it won't. But, if he doesn't understand already, you need to impress on the bike's owner that 43-year-old Britbike electrics aren't fit-'n'-forget like his car's or modern Jap bike's; he needs to check the battery water levels regularly, then he'll notice if the levels are dropping. wink

Hth.

Regards,

#438296 - 06/04/12 12:37 pm Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Aug 2010
Posts: 205
DaveOfTexas Offline
BritBike Forum member
DaveOfTexas  Offline
BritBike Forum member

Joined: Aug 2010
Posts: 205
Texas USA
Oh, boy this reminds me of a thread I started a while back!
http://www.britbike.com/forums/ubbthread...true#Post425359

I do have that Pacifico thing sitting right there!


1969 BSA B44VS PC8113
Engine PC8113B44VS
Recently acquired (Feb 2011) Aiming to get running and return all parts/configurations to original.
First BSA. Have 1970 Honda CB750 too.
#438328 - 06/04/12 3:01 pm Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Oct 2008
Posts: 1,654
LarryLebel Offline
BritBike Forum member
LarryLebel  Offline
BritBike Forum member

Joined: Oct 2008
Posts: 1,654
Canada
The Haynes manual says that at 15.5 volts the Zener diode diverts all the current from the alternator, about 5amps, to the heat sink, thus insuring the battery is not overcharged. So apparently you seeing 15v is OK.

#438335 - 06/04/12 3:43 pm Re: First Run Squawks - Voltage [Re: LarryLebel]  
Joined: Aug 2010
Posts: 205
DaveOfTexas Offline
BritBike Forum member
DaveOfTexas  Offline
BritBike Forum member

Joined: Aug 2010
Posts: 205
Texas USA
Larry that almost sounds like doublespeak!

The battery is seeing 15V but it is not being overcharged?

If I leave it, you all agree to send me a new battery in a month?!

Just funnin' ya.


1969 BSA B44VS PC8113
Engine PC8113B44VS
Recently acquired (Feb 2011) Aiming to get running and return all parts/configurations to original.
First BSA. Have 1970 Honda CB750 too.
#438337 - 06/04/12 3:52 pm Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Dec 2004
Posts: 8,883
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,883
Scotland
15V is at the top end of what a battery will tolerate but it will shorten its life eventually, I have a digital car battery charger and it charges the battery until it sees 16.3V and then stops and use it regularly and my car batteries last fine. For the moment until you csn get it down to 14.5V switch your lights on.

#438347 - 06/04/12 5:09 pm Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Aug 2010
Posts: 205
DaveOfTexas Offline
BritBike Forum member
DaveOfTexas  Offline
BritBike Forum member

Joined: Aug 2010
Posts: 205
Texas USA
OK I will watch it closely during the trials and run lights etc, see if it comes down, if the battery heats or boils.
Thanks.


1969 BSA B44VS PC8113
Engine PC8113B44VS
Recently acquired (Feb 2011) Aiming to get running and return all parts/configurations to original.
First BSA. Have 1970 Honda CB750 too.
#438354 - 06/04/12 5:52 pm Re: First Run Squawks - Voltage [Re: DaveOfTexas]  
Joined: Oct 2008
Posts: 1,654
LarryLebel Offline
BritBike Forum member
LarryLebel  Offline
BritBike Forum member

Joined: Oct 2008
Posts: 1,654
Canada
Dave. I'm just the messenger .... don't blame me.


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