motoradler Posted April 15, 2014 Report Share Posted April 15, 2014 Greetings all, So a couple of months ago I bought my first trials bike (exciting! ), a Montesa 311, spent much of the first two months just getting a feel for it- much different to the 4T's I'm used to! Anyway, about a month ago I noticed the fan wasn't spinning- yup typical story, fan burnt out, you know the drill. Checked off all of these- Fan- burnt out, new one on the way Thermostat- all good Wiring- Fine, current comes through However- on advice from a friend, I tested the regulator first to make sure I wasn't going to bugger up a new fan as well- and discovered its overvolting. I tested a 12 volt computer fan (definitely worked before, on a 12v car battery), first just hooked it up to the wires and turned the engine over slowly- did spin, but when I started the bike it spun for perhaps half a second then died. Now won't spin off a car battery, so pretty sure the bike burnt it out. Now I've been told to test the output from the rectifier to ensure its delivering the correct voltage to the regulator, but what should the correct voltage be on these, 20-30AC? Output for the Regulator I understand should be 12DC, but the yellow wire coming from the rectifier I have not test yet as I don't know what setting I should test them on the multimeter. Anyhow, apologies for the mass of text, if you can enlighten a total beginner it would be much appreciated. Cheers, EM Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 15, 2014 Report Share Posted April 15, 2014 Expect the voltage from the rectifier to be about 14 to 15 volts DC but it will fluctuate a bit, should show a steady ripple on an oscilloscope. Quote Link to comment Share on other sites More sharing options...
motoradler Posted April 15, 2014 Author Report Share Posted April 15, 2014 dadof2, on 16 Apr 2014 - 04:55 AM, said:Expect the voltage from the rectifier to be about 14 to 15 volts DC but it will fluctuate a bit, should show a steady ripple on an oscilloscope. Alright, will put a multimeter on it as soon as I can. Just don't want to blow up another one... if the rectifiers buggered though, what would the voltage be, a lot higher and AC? Cheers. EM Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 17, 2014 Report Share Posted April 17, 2014 I am not familiar enough with 311 electrics to know what the voltage would be if rectifier failed. Also it depends on just what fails in the rectifier and if its a combined regulator rectifier. Typically when combined regulator rectifies fail you can get voltage spikes anywhere between 25 and 85 volts, they are not really AC, just spikes. Typically a rectifier consists of a 4 diode layout and only one diode fails, and then only partially. A couple of recent examples spring to mind, a suzukis combined rectifier regulator was failing allowing the battery to drain when parked - this showed clear long duration spikes over 80 V on the oscilloscope. A ford fiesta had all sorts of peculiar intermittent electrical problems, oscilloscope showed many very low duration voltage spikes of both polarities to about 30V. Person did not want to buy a new alternator as car was due to be scrapped in a few months, fitting a large capacitor of a scrap electric motor suppressed the spikes and all electrical faults disappeared. Quote Link to comment Share on other sites More sharing options...
motoradler Posted April 18, 2014 Author Report Share Posted April 18, 2014 dadof2, on 18 Apr 2014 - 10:18 AM, said: I am not familiar enough with 311 electrics to know what the voltage would be if rectifier failed. Also it depends on just what fails in the rectifier and if its a combined regulator rectifier. Typically when combined regulator rectifies fail you can get voltage spikes anywhere between 25 and 85 volts, they are not really AC, just spikes. Typically a rectifier consists of a 4 diode layout and only one diode fails, and then only partially. A couple of recent examples spring to mind, a suzukis combined rectifier regulator was failing allowing the battery to drain when parked - this showed clear long duration spikes over 80 V on the oscilloscope. A ford fiesta had all sorts of peculiar intermittent electrical problems, oscilloscope showed many very low duration voltage spikes of both polarities to about 30V. Person did not want to buy a new alternator as car was due to be scrapped in a few months, fitting a large capacitor of a scrap electric motor suppressed the spikes and all electrical faults disappeared. Its a separate rectifier/regulator, if I understand correctly. The regulator's power comes from a yellow wire from what I assume is the rectifier, which is next to the CDI and the coil, and two wires come from the regulator, one goes to the thermo switch, the other straight to the fan. Cheers, EM Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 18, 2014 Report Share Posted April 18, 2014 As I said I am not familiar with 311 electrical system but from what you have said I guess it will have 3 to 5 AC generating coils to power the fan and lights. These will produce AC from about +/-10V at tickover up to over +/- 60 volts at high revs. THis power goes through the rectifier where the negative parts of the AC are flipped over to give a ripple DC voltage. The separate regulator then "clips" the tops off the voltage ripples at about 15 V leaving a near steady 12 to 15 V DC to power the fan. If the regulator has failed or is not earthed properly it will not clip off the high voltage that will then burn out your fan. The earthing arrangement varies depending on type of regulator, sometimes its via regulator body / base, sometimes by a separate wire. On a multimeter the output from the regulator should show about 12 to 14 V DC with maybe a bit of flicker, to see what is really going on you have to use an oscilloscope. Quote Link to comment Share on other sites More sharing options...
motoradler Posted April 21, 2014 Author Report Share Posted April 21, 2014 dadof2, on 18 Apr 2014 - 8:53 PM, said: As I said I am not familiar with 311 electrical system but from what you have said I guess it will have 3 to 5 AC generating coils to power the fan and lights. These will produce AC from about +/-10V at tickover up to over +/- 60 volts at high revs. THis power goes through the rectifier where the negative parts of the AC are flipped over to give a ripple DC voltage. The separate regulator then "clips" the tops off the voltage ripples at about 15 V leaving a near steady 12 to 15 V DC to power the fan. If the regulator has failed or is not earthed properly it will not clip off the high voltage that will then burn out your fan. The earthing arrangement varies depending on type of regulator, sometimes its via regulator body / base, sometimes by a separate wire. On a multimeter the output from the regulator should show about 12 to 14 V DC with maybe a bit of flicker, to see what is really going on you have to use an oscilloscope. Hiya, Had someone have a look at it, it appears to be an odd system, and mismatching from the manual also- it has a yellow wire coming from the alternator, by the looks of it, then it goes into the regulator, brings it down to 10-13 volts, then its got the little red box which was supposed to be the regulator, but we established is actually the rectifier- putting a TT125 reg/rect combo unit on it brought out 6 volt DC, but the Yamaha has two AC in wires, whereas the Montesa only seems to have one... As far as I understand, this is why we are only getting half the voltage, so would it be possible to splice the AC in into two channels for one of these units to get a 12V DC out? Cheers, EM Quote Link to comment Share on other sites More sharing options...
dadof2 Posted April 21, 2014 Report Share Posted April 21, 2014 Hi again Splitting one wire into two will not work. Can you post a photo of the stator. Once someone has changed something from original tends to be best to go back to the start. DC made from single phase AC (which is what you have with one wire) would certainly not be ideal to power a DC fan motor. Quote Link to comment Share on other sites More sharing options...
Aan_dres Posted August 8, 2023 Report Share Posted August 8, 2023 Hi there, I spend many time looking for some problems of the 311, because we get one a few weeks ago. The bike starts so good, but when you let it warm up it start's shutting down, and I'm looking what can be the problem. It have fuel, the spark plug seems to runs well too, but reading the electric problems maybe it has something to be with that problem. I don't know. If anyone have some issues like this or can tell me any advice I will appreciate it. Thanks! Quote Link to comment Share on other sites More sharing options...
lemur Posted August 8, 2023 Report Share Posted August 8, 2023 1 hour ago, Aan_dres said: Hi there, I spend many time looking for some problems of the 311, because we get one a few weeks ago. The bike starts so good, but when you let it warm up it start's shutting down, and I'm looking what can be the problem. It have fuel, the spark plug seems to runs well too, but reading the electric problems maybe it has something to be with that problem. I don't know. If anyone have some issues like this or can tell me any advice I will appreciate it. Thanks! Step one, obtain a service manual, step two test everything the manual tells you to check or inspect, step three tell us what your findings are and we can probably help you interpret the results. Probably best if you start a new thread unless you know for a fact that you have "over-voltage issues". If it is indeed an electric problem that only manifests when hot, I would start with inspection of the alternator coil and see if it looks like burnt toast, or if the coils internal resistance is correct. Electric issues are always best to troubleshoot starting at the source of power and working down stream. Quote Link to comment Share on other sites More sharing options...
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