Question about designing a high current regulator for a motorcycle. - Page 1
Forum section: electronics / beginners

author: pocoapoco
author_rank: Newbie
timestamp: July 17, 2014, 09:21:06 am
content: I work at a motorcycle shop and didn't know more than a typical village idiot's knowledge about electronics before just a month ago. Granted I still may be at that level of knowledge. What inspired me to start learning was a motorcycle that Id been working on for a customer. It had a blown regulator/rectifier unit, which is an easy enough repair with simple replacement normally. But in this instance, I ordered one that was bad right out of the box and then a second from a different source that was also bad right out of the box. So, being uite frustated with the state of affairs, I decided maybe try to build a unit. I bought some 30 amp three phase bridge regulators on ebay and just a 50 watt zener diode. It worked great for about 2 minutes until the heat-sinked zener overheated and failed. Next attempt, I tried to make a shunt regulator with a 20amp PNP transistor (mj15004a) and a lesser wattage (5w) zener controlling the base of the transistor, it failed too. As did the same circuit with a 30amp (mj11011) transistor. In both cases the transistor overheated and failed.I've been using this falstad simulator to plug in values for things as well as taking some measurements in the real world. I can't figure out why things aren't working. In the meantime I had ordered another production unit (which thankfully worked) due to running out of time. I also got ambitious and designed another unit with SCR's and a comparator which is a lot more complicated but my goal is to over spec the thing and make it really reliable as I've been seeing the quality of the OEM units really decline sharply in the last 10 years-more and more turning up dead.Before I go ahead and try to make a prototype I'd like to know if the circuit is even going to work ( as well as why the previous ones didn't ) The pnp reg4 attachment is the first attempt and the reg6 is the new design. They're both falstad files.Last thing, I have this idea that I'd like to get a setup to bench test electronic motorcycle components, especially spark units. What sort of equipment would I need to do this. I'm thinking like a basic oscilloscope, a function generator and almost certainly some sort of amplifier for the function generator as some magneto spark units have up to a 200vac input.

author: Simon
author_rank: Unknown
timestamp: July 17, 2014, 09:28:11 am
content: if you are talking the complete controller for an alternator you need to PWM the stator coil so that is changes with mechanical speed so that a constant voltage is matched, you sound like you have done this with a comparator which is good. Trying to let the thing run at full voltage and then heat dump excess power is a very bad idea and that is why all of your attempts failed. Basically you are building a very crude SMPS, you provide the control logic and power switch, the alternator is your inductor/transformer with a variable ratio due to speed and the battery is your output capacitor.

author: pocoapoco
author_rank: Newbie
timestamp: July 17, 2014, 09:36:55 am
content: Quote from: Simon on July 17, 2014, 09:28:11 amI'm pretty sure oem regulator/rectifier units are shunts as I've noticed that when motorcycles run with weak batteries or a headlight that's out the reg/rect unit will run substantially hotter. I can't really break into one and see what's going on because they are epoxy( or some other space-age chemical) filled.

author: Simon
author_rank: Unknown
timestamp: July 17, 2014, 10:00:50 am
content: if it's low power maybe. Most efficient thing to do then is replace the shunt with a SMPS block

author: sleemanj
author_rank: Super Contributor
timestamp: July 17, 2014, 10:04:31 am
content: Quote from: Simon on July 17, 2014, 09:28:11 amHe's talking about motorcycles not cars. Usually there is no field coil, it's a permanent magnet rotor, and yes, the excess is burnt off as heat after rectification.Quote from: pocoapoco on July 17, 2014, 09:21:06 amHere's a good run down on bike charging systems,http://www.electrosport.com/technical-resources/technical-articles/how-motorcycle-charging-system-worksa good place to start is to find out if your bike runs a permanant magnet rotor, or a field coil.Don't underestimate how much heatsinking you need, there is a reaon a motorcycle regulator looks like this, are mounted in airflow, and get hot.

author: mzzj
author_rank: Super Contributor
timestamp: July 17, 2014, 11:01:02 am
content: Quote from: sleemanj on July 17, 2014, 10:04:31 amAnother variety of motorcycle weirdness uses phase controlled thyristor(s) to shunt part of the cycle. (possibly more common than brute-force shunting to heat)Alternator is usually kind of current limited and thyristor bridge will shunt it as needed.ie something like thishttp://home.comcast.net/~loudgpz/GPZweb/RegRec/GPZvRegMagnetField.html

author: mikerj
author_rank: Super Contributor
timestamp: July 17, 2014, 01:56:00 pm
content: Quote from: mzzj on July 17, 2014, 11:01:02 amNearly all bikes with 3 phase permanent magnet generators have regulators that work like this. The older ones use SCR's and the newer ones use MOSFET transistors which allow the regulator to run cooler (lower on resistance of the MOSFET).Small engined bikes (e.g. 50cc mopeds) normally have a single phase charging system with a simple shunt regulator.