FET negative Shunt regulator

[la5tia59]

Hey guys. I'm new to this forum.
A friend of me have an old 1963 BSA motorcycle with 2 blown zeners in the regulator.
This bike have a 3 phase lucas alternator, and a 3 phase bridge rectrifier with the + terminal as a stud directly mounted to the frame. I would like to help my buddy and build a new regulator for him, but if some of you guys have some ideas to share I would be happy. I would like to use power fets.

Kind regards, Terje.

 

[MikeMl]

Look at my postings to this Previous thread.

Write back if you have trouble modifying this circuit for a positive ground. You will need a TO220 insulated mounting kit.

 

[la5tia59]

Dear Mike. Thank you for answer. It would be very nice if you could help me to modify this for +12v to ground if you don't mind.

Terje.

 

[MikeMl]

Since you didn't provide your location, I could not design with parts that you have easy access to. The parts shown are readily available in the US.

The circuit I am providing is good up to 7A; if the alternator on your machine puts more than that, we will have to modify.

The nominal regulation voltage is 7.1V, which is right for a lead-acid battery. With the bike parked, and with the battery voltage less than 6.5V, the circuit draws less than 500uA, so can be left connected while the bike is parked for a month or less. If you are parking the bike for more than a month, I would remove the battery from the bike, or otherwise provide a means from isolating the battery if the bike is inactive for months at a time.

When the bike is running at high speed, the battery fully charged, no lights turned on, then the regulator must dissipate almost the full output of the alternator. I dont know what your alternator can put out. You should measure it to make sure that it is 7A or less.

The bulk of the wasted power goes into heating R8, the 1Ω 50W tubular ceramic wire-wound resistor. Look at the plots. The red trace is power dissipated (Watts) in R8 as a function of the excess current being shunted (the X-axis). Since at 7A R8 dissipates 50W, it must be in good thermal contact with the steel frame of the machine.

Likewise, the green trace is the power dissipation in the TO220 NFET M1. It peaks at 12W at the 3.5A point in the trace, so the TO220 package must be bolted to the machine frame using a heatsink washer mounting kit.

The blue trace is shows the regulation voltage as a function of the current being shunted.

Give some feedback about how this circuit works out on the bike. Maybe we should include it in the "completed projects" section of this web site. Be prepared to take some pictures of the installation.

 

[la5tia59]

Excellent Mike. My location is Norway in Europe. Thank you so much for this. I only have to modify this for -12V. I will certainly try this in my friends bike. The parts should not be any problem. Since you seems to be really good in engineering I have another challenge as well I have an old American speedboat. A 35 year old Glastron Carlson with a Ford 460 with a water-jet. The engine is newly renovated due to cooling water in the exhaust valves. The scenario is as follows: the cooling water from the jet is forced into the heat exchanger and into the oil cooler and finally goes into the exhaust manifolds to mix with the exhaust in the risers to cool down this. I need to stop the cooling water with a electric operated valve 5 to 10 seconds before the engine stops. I have plans to use a stainless steel ball valve operated with a vacuum cylinder from the vacuum in the inlet manifold since i have 20HG inch vacuum at idle. this cylinder I can run with a solenoid valve. In my mind it must be some kind of timers and it should work like this: when I turn off the ignition key the valve for the solenoid is engaged and the cylinder is closing the valve. The engine should then run for 5 to 10 seconds to empty the water in the exhaust before it stops. When the engine have stopped the solenoid for the valve control releases. Next time I start the engine the solenoid is off until I turn the key off again, and the same scenario again. What do you think Mike?
Again, Thank you so much for the charging schematics.

Regarding completed projects, That would be cool. I will for sure shoot some pictures.

Terje.

 

[debe]

The water injection in the ex risers should be at least another foot along the ex pipe. Its no wonder water is geting in the ex manifold. Very poor design for a marine exhaust system.

 

[la5tia59]

Hey.
The problem is not the exhaust, but the space in the boat.. Regarding the exhaust system, this is Hardin Marine and the reason for that the water is hitting the cylinder heads is that the exhaust is going out below the sea-level. that's why I need to empty the riser due to back-pressure.


Terje

 

[MikeMl]

I missed the 12V requirement. This would regulate at -14.2V. The max current is now 4A or less.

 

[la5tia59]

Thank you Mike. What kind of program do you use to simulate this?

Terje.

 

[MikeMl]

Thank you Mike. What kind of program do you use to simulate this?

Terje.

LTSpice. Free download at Linear.com. Huge installed base and active User Group on Yahoo.

 

[la5tia59]

LTSpice. Free download at Linear.com. Huge installed base and active User Group on Yahoo.

Cool. I need to check this out....

 

[2wheelsenough]

I missed the 12V requirement. This would regulate at -14.2V. The max current is now 4A or less.

I missed the 12V requirement. This would regulate at -14.2V. The max current is now 4A or less.

Hi Mike
I’ve used the 6v shunt regulator on my fifties motorbike with some success.
I’m converting my other 1950’s motorbike from 6v to 12v, negative earth to match the electronic ignition I built.
I think it’s a good idea to use daylight run lights, although this wasn’t a great success when I tried it with 6v, replacing the 2.7 ohm resistor with a bulb in the 12v regulator could be more successful. I’ll let you know how I get on.
Also the drain on the n-fet is the same as the tag, are there any that use a different connection to the tag? This could be useful dumping the heat into the frame if it was the same potential as the ground, in my case negative ground.
All the best
Graham
2wheelsenough