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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 11-17-2012, 03:22 PM   #1 (permalink)
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Checking the charging rate on a T-120

Hi All,

When I try to check the running voltage at the battery on my '71 T-120 I see the readings range from 5-6 volts to high 13s. I am using one of the cheap multimeters set on 12V.

The voltage reading just seems to rotate through a cycle of several different readings but the high one is repeating pretty consistently.

Is this just a quirk of using a digital meter? I have noticed this before and was checking it again after replacing the Zener Diode (replaced for another reason).

The alternator seems to be charging as I can remove the main fuse and the bike will continue to run, even with the headlight on. Of course, with out the battery in the system the light goes very dim at idle (slightly less than 1000 RPM) but brightens up as soon as the RPM picks up and does not die at idle.

Anything to worry about?

Art
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Old 11-17-2012, 05:03 PM   #2 (permalink)
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It's obviously still charging and making more than 5V.
Some electrical interference from the engine is upsetting the meter.
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Old 11-17-2012, 05:05 PM   #3 (permalink)
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Opps, sorry for the post, answered my own question.

I was rummaging around in a cabinet putting things away and stumbled across an old analog volt meter that I forgot I had. It reads normally with a high voltage of about 14V at about 2000 RPM, no lights and about 13V with the lights.

Obviously it will require charging the battery occasionally as the "lights on always" law will not allow me to operate with out a light in the daytime but I expected that.

All's well, Art.
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Old 11-17-2012, 05:07 PM   #4 (permalink)
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Thanks Mr. Pete, your post came in while I was adding mine.

Art.
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Old 11-18-2012, 02:28 AM   #5 (permalink)
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Birdoprey.......i have a multimeter, and would like to check my charging system. are you saying that all that you need to do is set the meter to 12v and check it at the battery while running? or do you check it elsewhere? thanks, Rick
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Old 11-18-2012, 05:23 AM   #6 (permalink)
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Razman for a quick check measuring the battery voltage is ok. Any worries just ask.

Measure the battery voltage before you start your bike with lights and ignition off.

Measuring the voltage at tickover is generally meaningless as most bikes need some revs to start charging.

Measure the voltage at 2000 and 3000rpm with lights on and off. The battery voltage should be higher than before.
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Old 11-18-2012, 12:24 PM   #7 (permalink)
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The rough rule for charging most 12V batteries is 13.8V-14.2V. Remember, this is rough rule so check with the manufacture's recommendations. However, it's been this way for as long as I can remember, it's just what 12V batteries need to maintain themselves.

If the charging system will maintain that level then you are good to go. In other words, if there is that much voltage that finally reaches the battery after everything else, the battery will be maintained. Unfortunately, these old bikes were never intended to be ridden with the lights on all the time (all appliances on the bike will siphon away some power) so eventually the charging system will "get behind" and need some outside help.

Once you have determined that the voltage to the battery is insufficient (that is, based on a realistic assessment of the capabilities of the system) then you will need to start checking through out the system to try to identify what needs to be "fixed" to return the system to it's normal level of performance.

To check the status of the battery (ie. it's state of charge) check the battery voltage with everything turned off (static charge). Then, turn ignition and all the lights on (engine not running) and see what the voltage drops to. This is a crude "load test" and will give you an idea of just how much power is stored in the battery. If you do this when the battery is relatively new and fully charged you get a base line to compare to for the future.

If the static charge drops under load, from say 12.5V to perhaps 10V you can feel pretty confident that the battery is in fairly good shape.

If the static charge is 10-11 V that suggests that it is in a state of discharge, and, if you just charged it, let it set for an hour or so, and this is all you get, then either the battery is starting to fail or however you charged it didn't really do the job.

If the static charge is good but under load it drops to perhaps 8V or lower, that suggests that the battery may not be up to the task.

These are just some rough rule checks that you can perform with very basic tools. If you find any of this helpful that is all I have to offer.

Art.

Last edited by BirdoPrey; 11-18-2012 at 04:27 PM. Reason: sp.
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Old 11-19-2012, 12:21 AM   #8 (permalink)
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thanks guys! that helps a bunch! Rick
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