I have one more completely the same. A small engine shop has one too. Friend of mine runs it. And the local supplier who sold these machines has a few too. So a fix would be handy. And some advice on how to adapt this circuit to most small gens. This topic was started by a guy with a Honda Gen. I would think it can be adapted to his machine.
I hope this engine failure was just this one.
Over the weekend I plan on checking the full excitation current and how the excitation voltage/current has to change as load is added. Wish me luck with this engine LOL
Stew

 

Hi Stew,

Any small generator AVRs I have seen work the same way. Even your cars altenator regulator works in a similar way.

I have updated my AVR schematic... there were errors and omissions. The tool I use (LTspice) can simulate the circuit function as well. Q1 seems to be a good choice base on the info you provided before the connecting rod went. However, there is likely not enough heatsinking for Q1.

Can you measure, or estimate the ambient temperature around the regulator board when the gen is running at full load on a hot day in the summer?

The worst case power dissapation for Q1 appears to be 61 Watts, which would raise its internal (junction, Tj) temperature 73.1 degrees C above its case temperature (Tc). The max Tj is 175C, but this can quickly be used up if Ta is allready high, say 40C, and the heat being generated by Q1 cannot be dissapated properly. I.E. poor heatsinking. Q1 needs to be mounted in such a way that the case temperature is as close to ambient as possible.

The current design is obvously poor, so simply replacing bad parts it is not good enough... you have to make it better. I'm going to look at my 5000W Powermate to see what could be done.

To leave no stone unturned you should check diodes D6 and D7. If D6 opened then back emf pulses from the inductive field coil could have damaged Q1 also.

Regards, Wayne

 

I would have to ask but I think these machines failed during cold weather. Below 32 f because they were both for back up power for homes and we loose the power mostly in winter here in Nova Scotia. I have a temp probe for my Multimeter so I will check the temp rise in the area the board is located. When did you buy your machine? These are about 1 1/2 years old with almost no use. So they didn't have much on time to cook the board. If yours is older maybe it has a better board. I hope to get time Sunday to get more data from the generator and test the parts.
Stewart

 

Thanks nagaloo and ifixit for all the great effort. I'm attempting to link to a schematic of the Honda generator as I thought it might add some insight on possible inputs to the AVR. I noticed specifically how they tap the stator at a different point apparently limiting the input voltage to the AVR. I need to run the same tests as nagaloo but like him my engine is down at the moment (but it's not terminal). Hopefully the link will work.
Legend:
OW = Output Winding (stator)
AW = Auxillary Winding (excitor)
FW = Field Winding

http://picasaweb.google.com/lh/photo/kYqhPS2_OJn7mRmB13FDNA?authkey=FK7Eter-fMk&feat=directlink


Thanks,
David

 

Hi David,

The link worked okay. The Honda connections are very similar to the Colman except that it uses the stator tap (lower voltage) as feedback to control the field strength. This is likely to avoid routing high voltages on the control board for a less expensive (for Honda) design.

Generator 101...

These small, inexpensive generators can not use perment magnets to make the field as this is too costly, and you can not control the output voltage easily. Therefore, an electro-magnet (field winding) is used. The problem is that in the begining there is no voltage to energize the field with. One way to solve this is to build in a sensitive excitor winding that generates a voltage from residual magnetic field that is put in part of the stator iron core. You only need to put 200 Watts or less into the rotor winding to get 5000 Watts from the stator winding. The rest of the power comes from the rotational energy supplied by the gas engine.

The stator voltage is fed back to the AVR which compares it with an internal reference voltage (zener). The circuit will adjust the field strength up or down as required to keep the line output at 120 VAC when a load is applied. When a load is applied more magnet flux is required so the field voltage will go up. When there is no load the field voltage will be minimum.

What are your plans.. Fix AVR board, design new replacement, or buy new one? If you're going to fix or replace you'll need to make measurements like Stew did.

Hi Stew,

I couldn't get my Colman (bought in 2005, ~25 hours run time total) to start, so couldn't make my own temperature measurements. Gas not getting thru... no time to investigate. It's USA made, model PC0525303. I can see thru the vents that I likely have the same (or similar) AVR board as you. I can't see board model numbers.

Lets just assume a worst case ambient temperature of 40C (very hot summer day). This means our heatsink design must be such that it does not allow the Q3 case temperature to exceed ~100 degrees C. or more than 60C above the ambient at the time you measure the case temperature. I can help with heatsink design once your assessment is complete.

I my previous post I refer to Q1... this wrong ... I ment to say Q3.

Regards,

Wayne

 

Well here are my additional measurements from gen # 2
I started with a 100w light bulb mostly for a indicator that I was getting output at all and again I was using the 120 v to check output.
100 w 120 v .8 adc 27 vdc
+ 1200 w 120 v .8 adc 31 vdc
+ 1200 w one on each side of the output 120 v 1.2 adc 42 vdc
+1200 w 120 v 1.6 adc 59 vdc
Just 100 w bulb and excitation maxed 140+ v 2.4 adc 87 vdc

I was adding more load each time but couldnt scrounge up a really heavy load. Late sunday night and I should have been home already LOL

Notes
David
I have rewound honda gens of many different types. You are correct in part about the taps. They come from low turn coils wound in with the main winding and connected internally in a strange way. Mostly I think its just to make it hard to correctly record the data for rewinding. They are seperate but also connected to the main winding. I would have to look one up in my data sheets to explain it better.

Wayne
Some hondas have a small PM in the rotor to make them more reliable to start generating. The part that bites me about gens is we have an old timer that has no regulator and I have to get it out of storage and get the engine working right so I can do some output tests on it. All it has is a exciter winding with a CT and a bridge rectifier that only has 3 terms used on it. AC/AC and the positive the CT goes to the negative brush. If I remember right. When I get a look at it I will come back and post my data here.
So is there a device more capable for Q3 or would more heatsink solve it. From my data it seems voltage is more changable then current. I was told the device was able to take 10 amps at 400 v.
I am going to test my parts today to see if any other stuff is bad.
Stewart

 

Hi Stew,

Q3 should be okay as far as voltage and current because your tests indicate the excitor max voltage is 87V and max current is 2.4 amps. The Q3 specs are 10A max and 400V max so we're okay there. The max power dissipation allowed is 125W max, but this assumes your design can maintain the case temperature at 25C... most situations can not do this so the max power spec must be derated to suit.

The field winding and the transistor are connected in series across the excitor voltage of 87V max. From your measurements the winding resistance appears to be 32 to 35 ohms. The resistance of copper varies 0.4 percent per degree C. so the resistance will vary.

Using ohms law you can see that as Q3 conducts from barely on (75 ohms) to full on (1 ohm) so there will be a worst case power dissipation point for Q3. E.G. 0.8A X 60V (87-27) = 48W, 1.2A X 45V (87-42) = 54W, 2.4A X 1V (87-86) = 2.4W. This worst case point is when the voltage across the winding is equal to the voltage across Q3.

This generators worst is somewhere around 54 Watts, the other gen was 61 Watts. 61W causes the internal temp to rise by 73.2C obove case temp. 73.3 + 25 = 98.3C. Q3 s max is 175C. Emagine the heat of a 60W light bulb being dissipated in a small package like Q3... it gets very hot, very fast... if you don't take the heat away.

I am assuming the excitor voltage does not drop very much from 87V when the field current is max. Is this correct?

This is why I say you need to have more heatsink... the PCB is the only one you have now. I hope there is lots of air flow because the design needs all it can get. Adding a couple of square inches of 60 thou thick aluminum, bent into a U shape and place between the PCB and Q3 should help to get the heat into the moving air more effectively. Ensure contact area is smooth and flat. Use thermal grease aswell.

Regards,

Wayne

 

So the circuit looks good just not enough heat removal. What about adding a heat sink that isnt directly bolted to the board? There is room to stand the Q3 up. The big capacitor is the highest device on the board.
Stewart

 

One more point. Does anyone here have the means to print a copy of this PCB so it can be used to make a transfer to a photosensitive treated copper clad board for making a duplicate and also for making one just for any gen. with out the holes like this one had to fit around the bearing and brush holders in the endbell of the gen. And advice on what devices need to be adjusted in value to adapt it to another gen.
Thanks for the help on this and I hope this works for Davids machine.
Stewart

 

Hi Stewart,

If Q3 is stood up, its legs are subject to breaking from vibration if you don't secure things well so be aware of this issue. Whatever design you come up with needs to withstand the viberation.

Would photocopying the PCB work?

Regards,

Wayne

 

Well I wondered if the program you used for the circuit diagram would turn it into a print for making a board. Trouble with photocopying the board is there is a lot of stuff other then copper traces on it and its got a coating on it that makes it hard to see. I have used Autocad before for small simple circuits but was hoping there might be someone who could make a nice clean print of this one way or another.

I found one of the small diodes is shorted. But there are 2 the same and am not sure where the bad one was on the board. I was having trouble with my meter and have not resolved if the transistors are bad yet, I need new batteries.

I planned to add a additional heat sink that held the device as well as being attached to the board. I will post a pic when I get it done.
Stewart

 

Hi Stew,

If the Generator failure mode was no output (0V rms) then the shorted diode is likely D7 (1N4006) otherwise its likely D6 (1N4006), if it failed with max output (142Vrms). How did it fail? My schematic has an error... D6 and D7 should be swapped.

LTspice doesn't do PCB layout. There are free layout tools online... google: PCB layout.

I got my gen to run today. Lots of air is drawn in around the PCB and seems to exit at the other end of the gen near the engine... this is good.

The BU93T (Q3) is a tuff transistor and is designed to run hot and to work in this kind of application. I'am anguish to here if it tests okay. It is a darlington (b-e resistors built-in) so it may not test with a simple meter. You can use a 9V batt in series with a resistor (lamp?) across the emitter-collector, then drive the base-emitter with a 5K res from +9V to base... lamp should turn on.

Do all the generators have burned PCBs? Could the heat have caused Q3's pin soldering to melt and open?

Regards,

Wayne

 

I am getting the second boad back tomorrow to check to see if the same diode is bad on that one. The 2 I have and the one my buddy has all scortched the PCB and they failed with 0V output. One had melted the solder and burnt a copper trace off the board. I resoldered it and put some jumpers on it but didnt know at the time to check the diodes but suspected another bad device when it still wouldnt work.
So should that diode have a higher amp rating and PIV rating?

 

Hi Stew,

The diodes are 800V PIV and should never see more than the excitor voltage when all is working. If Q3 turns off during operation the diode will see the same energy that was being put into the inductor (field winding) at the time. Although it has a good surge rating it may be too much, too often.

I'll see if I can measure the field inductance tomorrow.

If Q3 trys to conduct with a shorted diode across the field this could cause serious overheating and failure of Q3 quickly.

My gen surges high-low for a few minutes until it warms up and then it smooths out and runs normal. I never load the gen until the speed settles down. The manual says this is normal. I'm wondering if the gen was loaded during this surging if it might be damaging the AVR. Do you think that's possible? Have you experienced this surging?

Regards,

Wayne

 

My birthday was on the weekend and the shops been busy this week. The second machine runs very bad till it warms up. I am going to get the AVR my friend has to check whats bad on it #3. When I did a quick test of the small transistors I have unsoldered they seemed bad but I didn't confirm it yet. The #2 board I unsoldered one end of both small diodes but neither were bad on that one. I will be back when I check on #3 and do some more testing.
Stew

 

Hi Stew, Happy Birthday.

The field winding seems to measure 6 Henrys with an LCR meter. The back EMF current the 1N4006 diodes will see if Q1 turns off is equivilent to what Q1 was conducting at the time. Max is 85V/27ohms = 3.1Amps for approximately 300mS. The 1N4006 has a max continious rating of 1A, and non-repeative peak rating of 30A max for 8.3mS. The diodes should be okay with a 3A pulse lasting longer so long as the pulses do not repeat too often.

Waiting to hear of more test results...

Wayne

 

nagaloo, dmechanic,
Any luck getting your avr's working? I have an Echo generator with avr problems, and like you I'm looking for a reasonable replacement or repair.

 

Know any thing about kohler 40m21 old rec. generator. worthwhile repairing.

 

Do you have the failed regulator board out of the unit(s)?

 

hi,
I'm doing a similar project.. i have to design an AVR for a single phase alternator(220v, <10 KVA).The existing AVRs have a feature of underfrequency shut down... i.e. below a specified frequency, which can be adjusted by a potentiometer...
Kindly suggest me a frequecy to voltage converter IC which is low in cost..

sir if you would be kind enought to send me the diagram of this avr with component thanks my email is aman2k4@hotmail.com
and thank you in advance