T500L not charging enough when lights on

[malky]

Hi all I have a problem with my T500L in as much as it only shows a charge voltage maximum of 13volts with the lights off and about 12.4 volts max with the lights on so is running the battery down if I use the lights - it just about manages to hold its own without them being on anyone have any suggestions
Mal.

[Alan H]

As I understand, the T500 has a similar charging circuit to the T200.
Position 1 on the ignition switch is 'everything off'.
Position 2 is 'ignition on' plus power from battery to horn, brake lights etc.
Position 3 is (same as 2 plus) extra charging coils connected to the rectifier.
Position 4 is parking lights only.

So, you need to check that the extra switch contact is ok and that the extra coils are working.
Also that the rectifier is working properly - if a diode has failed, then it will only charge the battery slowly.
Of course, if you'd have taken the rectifier that I took to the IOM last week, you'd have been able to try that.
(Good in the IOM though wasn't it???)

[ConnerVT]

Are these voltages you measured at the battery?

My gut feeling is there is voltage loss along the wiring. The 1970's weren't a grand time for wiring, and the T500 is notorious for poor connections, marginal switches and just enough wire gauge.

A time consuming process, but going through the entire harness and evaluating every connection will likely find the issue.

[jabcb]

The wiring diagram for the T500 is:


Instead of just cleaning up the existing wiring so that you get enough alternator output, you could also upgrade to a modern rectifier/regulator. They are more efficient so you’ll get more alternator output. Plus you can upgrade to a maintenance free or AGM battery.

I’ve used a Tympanium on several bikes with good results. There are good alternatives available in the UK.

How I mounted the Tympanium on a T500:


Wired it up for full alternator output all of the time. With the R/R you’ll get a max of around 14.3V. Modified diagram:

[Alan H]

Where's the hooraah button!!!

[joolstacho]

I think the alternator has a seperate lighting coil which cuts in when the lights are on, perhaps that's u/s.

[jabcb]

Agreed.

Look at the wiring diagram lower left corner. Lighting switch wires, SE & C2, control the alternator lighting coil.

The modified wiring diagram bypasses SE & C2. A modern rectifier/regulator does a good job of controlling voltage with full alternator output when the lights are off. The modern diodes in a modern rectifier/regulator are around 7% more efficient that the selenium diodes in the stock rectifier, so you also get more alternator output.

The stock setup relies on the battery regulating the voltage. The stock voltage regulator just makes sure the voltage doesn’t exceed 16V. That 16V is way too high for maintenance free & AGM batteries.

[karl pa]

The stock setup relies on the battery regulating the voltage. The stock voltage regulator just makes sure the voltage doesn’t exceed 16V. That 16V is way too high for maintenance free & AGM batteries.

The price of obsolete headlights, it is worth the upgrade.

[malky]

As I understand, the T500 has a similar charging circuit to the T200.
Position 1 on the ignition switch is 'everything off'.
Position 2 is 'ignition on' plus power from battery to horn, brake lights etc.
Position 3 is (same as 2 plus) extra charging coils connected to the rectifier.
Position 4 is parking lights only.

So, you need to check that the extra switch contact is ok and that the extra coils are working.
Also that the rectifier is working properly - if a diode has failed, then it will only charge the battery slowly.
Of course, if you'd have taken the rectifier that I took to the IOM last week, you'd have been able to try that.
(Good in the IOM though wasn't it???)

we had a good time out there Al - hard to believe we have been home a week.I appreciated you taking that rectifier over with you but the bike was holding its own as long as the lights were off - we changed the rectifier for the new one that you told me how to wire up a while back that was sitting on my shelf at home ready to change this afternoon and its still charging at a low rate struggling to get to 13volts at 5k revs so it seems that the rectifier is not the problem - how do i go about checking the alternator output - there`s a green/yellow wire and two red/green ones coming from the alternator which go to the rectifier via a voltage regulator - the ignition switch only has three positions - off - on and parking lights - the regulator doesnt seem to come apart as it sealed with compound

[malky]

The wiring diagram for the T500 is:


Instead of just cleaning up the existing wiring so that you get enough alternator output, you could also upgrade to a modern rectifier/regulator. They are more efficient so you’ll get more alternator output. Plus you can upgrade to a maintenance free or AGM battery.

I’ve used a Tympanium on several bikes with good results. There are good alternatives available in the UK.

How I mounted the Tympanium on a T500:


Wired it up for full alternator output all of the time. With the R/R you’ll get a max of around 14.3V. Modified diagram:

cheers I swapped the rectifier for a modern one earlier and it still has low output struggling to get to 13v One thing is that I am using an AGM battery already so should I not use one without modifying the stock rec/reg units?

[malky]

The wiring diagram for the T500 is:


Instead of just cleaning up the existing wiring so that you get enough alternator output, you could also upgrade to a modern rectifier/regulator. They are more efficient so you’ll get more alternator output. Plus you can upgrade to a maintenance free or AGM battery.

I’ve used a Tympanium on several bikes with good results. There are good alternatives available in the UK.

How I mounted the Tympanium on a T500:


Wired it up for full alternator output all of the time. With the R/R you’ll get a max of around 14.3V. Modified diagram:

that looks good - take it that it has four wires coming from it - do you by any chance have a link to a supplier? all the one I can see only have two yellow wires

[karl pa]

One thing is that I am using an AGM battery already so should I not use one without modifying the stock rec/reg units?

The problem with using AGM batteries without doing the Reg/Rec upgrade is that the stock charging system puts out to much voltage and will cook the AGM battery dry, leaving it useless. The one I cooked dry had good voltage but had no amps left in it. The recommended highest voltage for AGM is 14.2, much above that and you can run into trouble.
Is your low voltage at idle or higher rpm ?
You can check the yellow/green wire to ground using AC volt meter and red/green wire to ground again using AC volt meter also the green/white from the alternator to ground using AC volts. The green/white is the lighting coil, it goes to the headlight switch and then to rectifier as red/green, if the switch is giving trouble, the red/green should show low or no volts. Again all testing between alternator and rectifier has to be checked using AC volt meter, and bike running.

[jabcb]

Something is amiss. As Karl suggested, testing the alternator is a good first step.

This T500 wiring diagram shows how the alternator is wired up:
download/file.php?id=690

Alternator output has 3 wires: G/W, R/G & Y/G
The R/G + Y/G circuit is the charging coil.
The G/W + Y/G circuit is the light coil — it’s switched on/off by the left handlebar light on/off switch.

To check the alternator:
1) disconnect motor wiring & disconnect battey
2) check resistance between alternator wires R/G & Y/G, and G/W & Y/G. Should be around 1 ohm.
3) check resistance between ground & each alternator wire (R/G, Y/G & G/W). Should read as open circuit.

Karl recommended doing an alternator AC check.
1) with the motor wiring connected & the rectifier, regulator disconnected & motor running
2) check AC voltage for both circuits (charging & lighting coils)
For the stock T500 diagram — see wiring connectors to rectifier.
Check AC voltage for Y/G & either R/G. Then Y/G & other R/G

[karl pa]

Jabcb is correct, you want to check wire to wire for AC volts not wire to ground as I said.
I did a test on my 75T500 and had the following
Reg/Rec unhooked wire to wire around 40-48 volts AC
Reg/Rec hooked up wire to wire around 14-16 volts AC
DC output around 13 at idle.
Checking between the G/W in the multi wire plug and the R/G coming from the main wire harness coming from headlight bucket, with light switch turned off I had around 14.5 volts AC, with light switch turned on I had 0 volts, this is because the switch was made and the phasing was the same, showing a working light switch.

[malky]

One thing is that I am using an AGM battery already so should I not use one without modifying the stock rec/reg units?

The problem with using AGM batteries without doing the Reg/Rec upgrade is that the stock charging system puts out to much voltage and will cook the AGM battery dry, leaving it useless. The one I cooked dry had good voltage but had no amps left in it. The recommended highest voltage for AGM is 14.2, much above that and you can run into trouble.
Is your low voltage at idle or higher rpm ?
You can check the yellow/green wire to ground using AC volt meter and red/green wire to ground again using AC volt meter also the green/white from the alternator to ground using AC volts. The green/white is the lighting coil, it goes to the headlight switch and then to rectifier as red/green, if the switch is giving trouble, the red/green should show low or no volts. Again all testing between alternator and rectifier has to be checked using AC volt meter, and bike running.

The reading is taken at 4k revs - it's struggling to hit 13v with the lights off and only gets to around 12.4 when they are on