Post by Diesel Forty on Nov 23, 2019 14:27:16 GMT -8
I'm starting a new subject to avoid any more interference with the one concerning the forum and Gary's situation.
I was wondering if the MOSFET regulator in the projects section could successfully be modified to control an alternator at 100ish volts. Volkswagenvan was good enough to respond with his recommendation. My main concern was if component values would need to be changed or if putting in a 100v zener would do the job. In working out the voltage divider it looks like the total current would be about 33 mA with a power of less than 4 W. That assumes no resistance in the zener itself. If that is correct, a 105v zener in the 5 W range would give me the output I need. Are my calculations right? I have worked as an electronic tech for some years but have not been heavily into the design end. Any insights would be greatly appreciated.
Post by Diesel Forty on Nov 24, 2019 15:13:03 GMT -8
That's what I am concerned with, how far into the system is the higher voltage felt? As I see it, the fet would only see the 12 v from the battery on the S and D terminals but how much is on the gate? It also seems as if the first 2N3904 might get too much on its base. Calculating the voltage drops across the 4.7K resistor and the B-E junction is where my designing abilities falter.
As for the alternator, I was very skeptical when I first heard about pulling higher voltage out of them. Since I have a pile of old alternators available I decided to try it out. By using a wye wound stator, a suitable external 3 phase bridge rectifier and putting about 10 volts on the field I was able to pull 100 volts at about 90 amps. The only regulation I had was engine speed, that isn't suitable for actual use but it worked for testing. There were no ill effects, overheating or escape of magic smoke. That system actually worked for a couple short road trips in my hybrid car. I had been poking around the internet for a couple years trying to find a suitable regulator, unsuccessfully until now. Although I would like to have gotten Gary's input on his design, I really appreciate the willingness to help.
Post by volkswagenvan on Nov 24, 2019 20:26:10 GMT -8
(I was very skeptical when I first heard about pulling higher voltage out of them.)
Heck i used to run power tools with them as a kid. Anything with carbon brushes. Had my old dodge truck set up with a switch to change from charge to power. Even had some old cruise control on it to rev the engine a bit. I did a bit of welding with one to! Alternators beat the hell out of generators. Fun times lol.
yea,... My designing abilities are full of failure and success . You gotta be patient and do some experiments to get experience.
Been thinking to hard I think...
I know Gary said the field winding still requires a 12 Volt Supply.
Looking at the circuit you can see that it is powered by a 12 volt battery and isolated from the sensing resistor that is on the alternators output. ( 1.8k) This circuit monitors the alternators output voltage and compares it to a Zener Reference. This drives the mosfet to control the current to the Alternators field coil. you may have to change out the 4.7k on the base of the first 2n3904 if it gets warm or just start with like a 20k pot. Experiment with it. You should be good to go with the existing circuit. Cheep to build. Change the 1 watt zener to 2 volts under the wanted output and give it a try. Just remember to keep the 12 volt supply separate.
I could be wrong. overheating or magic smoke could happen at any time with any first try! Just ask my wife. (what went bang and whats that smell) lol
Post by Diesel Forty on Nov 25, 2019 19:40:36 GMT -8
We must be about the same vintage, I remember the ads for those alternator switches but never tried one. They apparently worked all right but I didn't know how well they fared in the long term.
One of the things that attracted me to this regulator is that it uses a separate battery to power the field. I wanted to use the ship's battery for the field as opposed to trying to reduce the 96v traction batt to 12v so that is a plus. You are right about the experimenting, I too have a trail less-than-successful outcomes. As I get older I try to be a little more willing to get advice ahead of time and avoid unpleasant surprises! You're right about the fact that this project is cheap enough that a failure or two wouldn't be a major set-back. I guess I'll see about collecting the parts and giving it a shot. I'll keep checking in here for any further enlightenment and if the site is still up I'll report my results, good or bad.