Has anyone ever built a solid state regulator for a starter generator setup?

[JUSS10 250]

To me it seems like it would be possible. Couldn't you chain a few 5amp voltage regulator ICs together to knock down the voltage and ditch the mechanical regulator? I have had a few of these fail and it always seems to be the part that goes bad in the charging system. I know on some older motorcycles I have, I can get a solid state regulator to replace the mechanical relay style one just like what we have on these older tractors. Thoughts? before I go shell out money on a new one I thought I would ask here first if this is possible.

 

Justin

[JUSS10 250]

I just went ahead and bought a new one off ebay but I still wonder how hard this would be? 

[formariz 11,987]

There are at least a couple members here that seem to be knowledgeable enough to accomplish that. The same goes for modifying an analogue tachometer to be used on Kohlers. Probably would be a bit expensive but I think many of us would appreciate and use those services.

[Save Old Iron 1,566]

Hey Justin, just saw this post.

 

I.m not sure exactly where to start with my reply as I don't know how familiar you might be with the operation of an SG charging system. In relation to using linear regulators and devices (transistors, MOSFET's etc) for replacement of the mechanical relays, please understand the SG mechanical regulator provides 3 independent functions.

 

The CUTOUT relay provides a one way street for current to leave the SG and not "backwash" from the battery to the SG motor when the SG output falls below the battery voltage. This function can be easily replaced by a high powered diode. Really simple actually.

 

The second function of the voltage relay is to ground or unground the field of the SG motor to charge or stop charging the battery around a 14.x volt level. This is a pre-historic version of voltage regulation whose action is to constantly slam the relay on and off several hundred times per second. This slamming is what causes the relay contacts to "buzz" and pit over time.

The third function of the regulator is to lift the ground from the SG field coil when the SG motor produced more than 15 amps of output current.

 

 

The regulator does not simply "reduce" the output of the SG - it controls it. Both voltage and current regulation is controlled simply by either the voltage or current sense relays grounding or lifting the ground on the SG field coil.

 

I think your assumption may be to use a bank of 5 amp regs to knock down the SG output. And you could do that if you forced the SG motor to a full output state by permanently grounding the field coil. BUT ,,, and it's a big BUT - you would have to user the linear regs to dissipate the power from the SG by converting it to heat in the heatsinks of the linears regs !!!  That's some big heat sinks on the linear regs !!!! Each linear reg would drop at least 2 - 5 volts at 5 amps (20 + watts each in heat), each would require a high power balancing resistor to equalize the current draw thru each reg (so one doesn't take more current than the next, burn out and force others to take a greater share, have them burn out , etc resulting in a chain reaction of thermal destruction). You now have lots of linear regs, lots of equalizer resistors, big heat sinks and no real gains.

 

If you would like to pursue some investigation on how to control a DC generator by field current, consider a MOSFET operated in its linear resistance region. The MOSFET could be placed in series with the SG field coil and vary its resistance to just enough to excite the field coil to maintain 14.x volts from the SG. Keep investigating and pursuing your ideas but approach it from a standpoint of GENERATING ONLY THE POWER YOU NEED, not CREATING AND THEN DISPOSING of excess power thru linear regulators..

 

Chuck

Edited April 1, 2014 by Save Old Iron

[wheeledhorseman 574]

As Chuck says (of course)  , this can be done but it is a complex design challenge. For my jeeps which have a 24 volt electric system I developed a circuit to exactly replace the three coil electromechanical regulators which are NLA. I built two for myself and one for a friend and all three are still working after about four years now. Of course suddenly the world and his wife wanted me to build one for them too but I didn't have the time to get involved. It's very time consuming to build them one at a time and would have required significant investment on my part to get boards made and populated commercially.

 

A 12/14 volt circuit is actually easier when it comes to power MOSFETs than the 24/28 volt challenge but the route I took (much simplified) was to use the field MOSFET as a switch that was driven by a quad op amp that sensed voltage, current, and generated pulses to drive the MOSFET. Regulation was by the pulse width varying as the op amp compared battery voltage with a reference voltage, I even set things so the frequency of the pulses mimicked the frequency at which the mechanical contacts in the old regulator buzzed in normal operation.

 

There is a simpler approach and that is to adapt a regulator from a 12 volt alternator by adding a few components to drive the field coil. I rejected this to develop as an idea as whilst it would regulate voltage it would not have any current limiting features. It is the method (I believe) used by some of those offering solid state replacements for old motorcyles and cars etc. Limiting the current output from a dynamo is important whereas an alternator has an inherent self limiting feature by design.

 

Andy

[tbarnhart 240]

Andy, Would you be willing to share your circuit diagram? My brother is looking to build something of that nature. He has a '66 Sears Suburban that has a SG. We think we could use an alternator voltage regulator for that part, but wanted something for the amperage limiting. We were wondering how you did that. Thought too that an alternator voltage regulator might not handle the field current. Thanks

Quote from Andy

"A 12/14 volt circuit is actually easier when it comes to power MOSFETs than the 24/28 volt challenge but the route I took (much simplified) was to use the field MOSFET as a switch that was driven by a quad op amp that sensed voltage, current, and generated pulses to drive the MOSFET. Regulation was by the pulse width varying as the op amp compared battery voltage with a reference voltage, I even set things so the frequency of the pulses mimicked the frequency at which the mechanical contacts in the old regulator buzzed in normal operation."

 

 

Edited July 25, 2014 by tbarnhart