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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.
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Post by volkswagenvan on Nov 23, 2019 16:48:57 GMT -8
Looks good but you may have to get a fet that can handle the higher voltage that you want.
I see the P-channel stp80pf55 is good up to 55 volts.
Your asking alot out of a car alternator lol.
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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.
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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
Jerry
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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.
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Post by volkswagenvan on Nov 25, 2019 20:53:36 GMT -8
Sounds good.
Best of luck to you!
Jerry
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Post by blueskies on Oct 23, 2021 0:00:17 GMT -8
hi, can i use this regulator to control a 48v nominal (58v actual) alternator, rather than try and make a 12v alternator provide 48v. The rotor wiring of a 48v will be different to a 12v rotor. Will this regulator have to push a lot more amps into the rotor wiring and potentially burn it out if it is using 12v? Appreciate help in avoiding the magic smoke.
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Post by volkswagenvan on Oct 23, 2021 6:20:27 GMT -8
Hi blueskies.
If you are starting with a 48V alternator you should be fine.
The field should not draw any more than a 12v system field (give or take a bit) because it is designed to do the same job but at 48v.
You will have to experiment with your zener a bit.
Remember to use a mosfet with high enough voltage/current rating for a safety margin.
All in all it would work fine for your alternator. You just have to play with it a bit to get what you want.
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Post by volkswagenvan on Oct 23, 2021 7:56:36 GMT -8
I forgot one more thing,...
Make sure to use a high enough voltage rated dielectric and tantalum capacitor!
Magic smoke with loud report!
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Post by blueskies on Oct 24, 2021 1:29:37 GMT -8
Thanks for the answer/responding :-)
I don't mind playing with the regulator circuit and burning it's components while learning, so long as I hopefully don't burn the rotor field wire, which should be hard to do, but if anyone can, it will be me :-)
Not sure if my understanding is correct. Do you mean that I can use the same 48v battery that the alternator is charging as the regulator's source, instead of an independent 12v source, so long as I upgrade the mosfet and capacitors so that they are rated to handle the max voltage and also choose the appropriate zener and diode combo to get my desired voltage set point?
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Post by volkswagenvan on Oct 24, 2021 14:47:02 GMT -8
Your 48 volt alternator will have a field winding made for handling 48 to around 50 volts.
Burning up anything in the alternator would be hard to do at your voltage.
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Post by volkswagenvan on Oct 24, 2021 14:49:00 GMT -8
(Do you mean that I can use the same 48v battery that the alternator is charging as the regulator's source)
Yes!
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Post by blueskies on Oct 25, 2021 9:12:10 GMT -8
Thanks, in which case do I also need to change some of the resistor values to ensure the current into the transistors are appropriate, because of now having 48V instead of 12V? Plus, I don't get how the hysteresis resistor works, so not sure if I also need to change that due to moving to 48V. Since first looking at this circuit, I have learnt a bit about zener diodes, transistors, darlington pairs, shunt regulators and power supply voltage regulators. Luckily, I enjoy it and hopefully will understand the fundamentals of how this circuit works so that I can tinker with it. Hopefully you will bear with me as I ask low level questions. Thanks again!
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Post by volkswagenvan on Oct 25, 2021 19:54:52 GMT -8
There is no low level question!
The hysteresis resistor changes the voltage differential that the circuit takes to correct
any voltage change to try to keep it at the set value or voltage in your case. (Say + or - so many volts.)
Do you need to change the value? Try it and see.
The 1N5400 may work but a better choice may be a 1000 volt 1N5408.
You never know if a high voltage inductive spike will kill your project and make a bad day for you!
Looks like the voltage sampling and current sampling of this circuit is low so the resistors will be close
enough for you to experiment with without to much magic smoke. lol
Your on the right track!
Hope this helps a bit.
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Post by blueskies on Oct 26, 2021 2:00:28 GMT -8
Thanks for the extra info. Now what if I want to derate the alternator to 70% of it's maximum current output. How can I do that? Would a resistor in parallel to the field wire do the trick or is there a better way?
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