Problem Checking the Voltage Output On '66 T100

Big_Jim59

Big_Jim59

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My Triumph T100 has been sitting for most of the winter. I have tried to keep the battery charged but the battery seems to have gone flat. I charged it and it came up to read 12.32V at rest. When I start the bike and increase the RPM, with the digital multimeter leads across the battery terminals, I get all kinds of fluctuating readings from 10.6V to 9.4V and then back to 12.32V. (This is with the headlight off.)

Do I have an issue with my multimeter? It has a fresh battery by the way.

I have checked it with an analog multimeter but the scale is from 0-50. The needle moves in a positive direction but the gradient is so small as to be very hard to read.

Just so you know, I am running an older Lucas, 2 wire stater, a Podtronics R/R (without the starting capacitor) and a Wassell EI. The multimeter indicated that it was charging before I let the bike sit. (Or so I think.) Even now the headlight will get brighter when the engine RPMs are increased.
 
Big_Jim59 said:
My Triumph T100 has been sitting for most of the winter. I have tried to keep the battery charged but the battery seems to have gone flat. I charged it and it came up to read 12.32V at rest. When I start the bike and increase the RPM, with the digital multimeter leads across the battery terminals, I get all kinds of fluctuating readings from 10.6V to 9.4V and then back to 12.32V. (This is with the headlight off.)

Do I have an issue with my multimeter? It has a fresh battery by the way.

I have checked it with an analog multimeter but the scale is from 0-50. The needle moves in a positive direction but the gradient is so small as to be very hard to read.

Just so you know, I am running an older Lucas, 2 wire stater, a Podtronics R/R (without the starting capacitor) and a Wassell EI. The multimeter indicated that it was charging before I let the bike sit. (Or so I think.) Even now the headlight will get brighter when the engine RPMs are increased.
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The symptoms/info you report are consistant with a failed battery. The "Bermuda Triangle" readings.

The test must be done using a KNOWN GOOD battery.

Easy to do, simply remove your battery, temporary connect a KNOWN good battery from: another bike, lawn tractor, etc that is charged, using test leads.
Repeat the test, report the findings.

DO NOT use the electric start during using test leads.

You CAN use automotive jumper cables instead of test leads, (in which case you CAN confirm the electric start viability) but not needed to verify charge voltage.
3D8B972A-F402-4E36-A09D-AE6D36520AB3.png
 
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I'm thinking it's your DVM which is giving faulty readings because the noisy Podtronics unit is affecting it via emitted RF. A Fluke meter won't do this but cheap ones will. The fact that your headlight increases in brightness with revs means you're charging. You can filter the RF with a choke in series or maybe a capacitor combination in parallel.
 
Big_Jim59 said:
My Triumph T100 has been sitting for most of the winter. I have tried to keep the battery charged but the battery seems to have gone flat. I charged it and it came up to read 12.32V at rest. When I start the bike and increase the RPM, with the digital multimeter leads across the battery terminals, I get all kinds of fluctuating readings from 10.6V to 9.4V and then back to 12.32V. (This is with the headlight off.)

Do I have an issue with my multimeter? It has a fresh battery by the way.

I have checked it with an analog multimeter but the scale is from 0-50. The needle moves in a positive direction but the gradient is so small as to be very hard to read.

Just so you know, I am running an older Lucas, 2 wire stater, a Podtronics R/R (without the starting capacitor) and a Wassell EI. The multimeter indicated that it was charging before I let the bike sit. (Or so I think.) Even now the headlight will get brighter when the engine RPMs are increased.
Click to expand...
Most likely a bad motorcycle battery. Remove the fuse so the battery is connected to nothing (or disconnect one battery connection). Check the battery voltage. Connect your charger and check the battery voltage. If with the charger attached it climbs to almost 14 volts after a while that check is good. Disconnect the charger. If the voltage is not at least 12.6 volts, assuming your meter is good, replace the battery. To double check, do the check across the battery of your car with it running and not running - the motorcycle reading and car readings should be nearly the same.

Standard Digital voltmeters are about worthless for automotive and definity worthless for old motorcycles. A cheap analog meter is much better, unfortunatley all seem to have 10 and 50 dcv ranges when you would like ot have a 20 dcv range. I use this one because it's big enough that battery and charge voltages can be "close enough" read: Amazon product ASIN B000O02YRI
The battery in a multimeter is only involved when measuring resistance - has nothing to do with dcv, acv, or current.
 
I pulled the battery from my Norton. It was only showing 11.12V at rest so I am giving it a charge. I hooked it up to the T100 and gave it a test. The multimeter worked. The voltage only came up to 11.45V when revved. I just may have a bad magnet.
 
It's also possible the Podtronics is malfunctioning. You can measure alternator voltage on the AC setting. It should easily get into the twenties.
 
Big_Jim59 said:
I pulled the battery from my Norton. It was only showing 11.12V at rest so I am giving it a charge. I hooked it up to the T100 and gave it a test. The multimeter worked. The voltage only came up to 11.45V when revved. I just may have a bad magnet.
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Still probably a bad battery. To charge a battery the charger or bike system must hold the voltage higher than the battery voltage. If the battery is good, when you put it on a charger it will take time to fully charge.

What kind of battery (lead acid, AGM, Lithium?)
 
Big_Jim59 said:
Lead acid. Batteries are both on charger.
Click to expand...
If like most it has a translucent casing, you can hold it up to the light. If you see white "stuff" on the plates, it's over. Lead acid stored in the cold sulfate quickly and although some chargers profess to "fix" them, it is very unlikely to work if you can see the sulfate.

If you do get it fully charged, it will go down quickly. I recommend replacing it with an AGM battery and if the bike is stored in an unheated place, bring the battery in the house over the winter - not as important with AGM but still a good idea.
 
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marshg246 said:
I hear you screaming - who are you screaming at?
Click to expand...
NOT you Greg. Not you.

Maybe decaff could help.


I was responding to the OP with some quick, solid troubleshooting methods.
He used (not quite as) another duff battery, but proved SOME of the theory.

Best if you take over from here.

I'm out.
 
concours said:
NOT you Greg. Not you.

Maybe decaff could help.


I was responding to the OP with some quick, solid troubleshooting methods.
He used (not quite as) another duff battery, but proved SOME of the theory.

Best if you take over from here.

I'm out.
Click to expand...
No worries. You and I have been saying the same thing. I'm only trying to add a little education to the troubleshooting and have no more to add so I'm out too.
 
I have charged both the Norton battery and the T100 battery. I wrote down the voltage of both at the highest charge level. Tomorrow I will check each battery and see what kind of voltage drop I get.
 
I ran the test with my known good battery. My digital volt meter gave me a consistant reading. I have determined that the battery is good. The system is charging but not very much, maybe 0.6V increase. It's probably due to a weak magnet rotor. When I feel like throwing more money at this project I will get the rotor remagintized.
 
Big_Jim59 said:
I ran the test with my known good battery. My digital volt meter gave me a consistant reading. I have determined that the battery is good. The system is charging but not very much, maybe 0.6V increase. It's probably due to a weak magnet rotor. When I feel like throwing more money at this project I will get the rotor remagintized.
Click to expand...
Any increase in voltage over the battery voltage means the battery is being charged. Much higher and your lead acid battery would boil away the electrolyte!

If your battery was fully charged (and could be), you would have less than 0.6 volts increase.
 
marshg246 said:
Any increase in voltage over the battery voltage means the battery is being charged. Much higher and your lead acid battery would boil away the electrolyte!

If your battery was fully charged (and could be), you would have less than 0.6 volts increase.
Click to expand...
I expected it to be in the +13V range? Right now the battery shows 12.16V at rest and 12.46V when revved. I guess the old Lucas system is only meant to just keep the battery charged.
 
Big_Jim59 said:
I expected it to be in the +13V range? Right now the battery shows 12.16V at rest and 12.46V when revved. I guess the old Lucas system is only meant to just keep the battery charged.
Click to expand...
12.46V revved sounds pretty low. With a zener and a reasonably good condition battery, you can expect 14-14.5V. A battery with an internal partial short could make it low though.
 
hhh said:
12.46V revved sounds pretty low. With a zener and a reasonably good condition battery, you can expect 14-14.5V. A battery with an internal partial short could make it low though.
Click to expand...
It's on a Podtronics R/R. I charged the battery, checked it at full charge and it showed 12.46V at rest (noting connected). I checked it 12 hours later and it showed 12.16V.
 

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