Wassel unit faulty? EDIT: probably not

[Nerdy Norm]

I made the 12V DC Wassel conversion (with battery) a few weeks ago, as detailed elsewhere on the forum.

All seemed to be fine until I noticed that the battery was running down. Being lazy, I just charged it up and carried on as normal. Today, I thought I should get to the root of the problem so I got out the test meter.

The stator output seems fine with the yellows disconnected from the Wassel (around 11V AC when putting the meter across the 2 yellows at tickover, rising with engine revs). But when I connect the Wassel unit to the yellows, the same test gives only 1.5V one way and 4V if I switch round the meter probes.

I've checked all the earths and other connections, and they seem good. However the red output wire from the Wassel unit only outputs around 3V DC, which would explain the battery running down, as well as the lights not working from the engine either.

So my questions are:
1. Should the stator output measure so low when connected to the Wassel? It also seems strange that the reading differs according to which way I connect the test leads.
2. Assuming the above is normal (and that the stator is functioning correctly since its output without the Wassel connected is normal), does this point to a faulty Wassel unit?

The scooter is an LI 150 S3 with an electronic conversion carried out by a previous owner. Halogen headlamp, LED rear, no spots etc.

The parts I used are these:
http://beedspeed.com/wassell-rectifier-p-9204.html
http://beedspeed.com/lambretta-stator-p ... -9269.html
http://www.ebay.co.uk/itm/YUASA-12V-7AH ... OC:GB:3160

Thanks for any info

[Grumpy225]

When you are getting the low reading connected to the wassel are you connected to the battery at the same time? As always check your ground points and connections to eliminate something simple.

I have seen a few people have issues with alarm type batteries in scooters. Something to do with the battery not liking the pulse dc being produced

[Nerdy Norm]

No, the battery was disconnected but the lights were switched on to provide a load. All connections and earths appear to be good.

[Grumpy225]

I'd try again with no load from the lights. This way you eliminate a loom/switch issue.

[coaster]

I'd try again with no load from the lights. This way you eliminate a loom/switch issue.

You have to have a load applied to the Wassel otherwise it shunts everything to earth. As said, the best way to test is to connect the battery, the voltage should rise to 13 or so volts with the lights off. Switching the lights on will bring the voltage down a fair bit but with revs, it should be slightly higher than the battery volts with the engine switched off. At best the charge is going to be marginal if you ride with the lights on all the time (like I do). I also have to top my charge up from time to time especially if I make use of the pair of 35 watts spots I have fitted. 7.2 Aph alarm type battery.

PS, I don't believe that about 'pulsed' DC being bad for alarm batteries, most battery chargers only consist of a transformer and a rectifier which even if it's full wave, will still give a lumpy 50Hz DC output. Lap top chargers do have a capacitor in them to smooth the supply though.

[Nerdy Norm]

As said, the best way to test is to connect the battery, the voltage should rise to 13 or so volts with the lights off.

Thanks guys. I deliberately didn't connect the battery as I figured I'd then be taking a reading which would include the battery's voltage, since it's connected to the same red output wire from the Wassell. The battery's fully charged (by a mains charger), so I would imagine the reading I'd get from the red wire with it connected would be around 12V.

What am I missing?

[ArmandTanzarian]

As others have said. During normal operation, you should get a minimum of 13 to 13.5 volts across the battery with the engine running. I found that a burglar alarm battery wasn't man enough for the job and so I fitted a proper bike battery mounted in one of those under panel tool boxes that sit next to the back wheel.

[Nerdy Norm]

Thanks, I'll get the meter on it again tomorrow. I'd assumed (wrongly by the sound of it) that the red output wire from the Wassell would need to be giving 13 or 14 volts in order to power the loom and charge the battery.

[Grumpy225]

I'd try again with no load from the lights. This way you eliminate a loom/switch issue.

You have to have a load applied to the Wassel otherwise it shunts everything to earth. As said, the best way to test is to connect the battery, the voltage should rise to 13 or so volts with the lights off. Switching the lights on will bring the voltage down a fair bit but with revs, it should be slightly higher than the battery volts with the engine switched off. At best the charge is going to be marginal if you ride with the lights on all the time (like I do). I also have to top my charge up from time to time especially if I make use of the pair of 35 watts spots I have fitted. 7.2 Aph alarm type battery.

PS, I don't believe that about 'pulsed' DC being bad for alarm batteries, most battery chargers only consist of a transformer and a rectifier which even if it's full wave, will still give a lumpy 50Hz DC output. Lap top chargers do have a capacitor in them to smooth the supply though.

Dang it, now I have to roll out the oscilloscope and really see what's going on. Thanks for the clarification.

[ArmandTanzarian]

I don't think it was the pulses that my alarm battery couldn't cope with. I think it was just too small.