Back EMF smoke in controll panel

[mirocha]

Using Kflop and Kanalog in control panel to drive stepper motors. 4 Stepper motors are rated 5.7 volts , 3.5 amps and 22 (mH). Using Gecko G210 drives. Gecko drive is rated for up to 80 volts. Gecko recommends power supply voltage should be no less than 4 times or no more than 25 times the motor’s rated voltage. I first started with regulated a 48 volt power supplies but the Gecko drive went into fault condition and it turned out to be back emf on slow down of motor.

So I added the Gecko recommended Return Energy Dump circuit and added a diode, led and capacitor to the Gecko Return Energy Dump circuit so I could see when the Gecko Return Energy Dump circuit was shunting EMF and working. (see circuit below) It worked great and fixed my problem, when the stepper motor decelerated at a quick rate the Return Energy Dump circuit turned on and I could see the led light and slowly dim, it works great. Gecko states this circuit protects stepmotor and servomotor drives from damage during periods of energy return when operating near maximum rated voltage.

After posting on this forum my problem I revcieved help to fix the problem and I received several recommendations to change the regulated power supplies to unregulated diode/cap power supply.

I upgraded to an unregulated 70 VDC 800 watt power supply which is near maximum rated voltage of the Gecko G210 and installed the Gecko Return Energy Dump circuit, one on each of the 4 stepper motors.

I am bench testing everything with the steppermotors c-clamped to a table with no mechanical load that would increase the back EMF.

Ran the motors and the Gecko Return Energy Dump circuits worked fine then after running at different speed several times the Gecko Return Energy Dump circuits started burning up with clouds of smoke. I saw the LED's stayed lit telling me the TIP 147 transistor shorted out and the 33 ohm resistor was burning up because the shorted transistor kept power through the resistor.

Gecko circuit



Circuit I added the diode, resistor, LED and capacitor




I don't know if the back EMF voltage or current is now the problem with the higher voltage power supply, the TIP 147 transistor in the Gecko Return Energy Dump circuit is rated for 100 volts at 10 amps.

Does anyone have a suggestion on a circuit design or a transistor to use in the Return Energy Dump circuit hat would handle the higher voltage and current of the back emf. I do want to stay with the higher voltage power supply.

I am now afraid not to use a Return Energy Dump circuit for fear of burning up the Gecko drives, the cloud of smoke from the Return Energy Dump circuit raises my concern.

Thanks Joseph

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[Jim Dawson]

I don't see anything that pulls the base of Q1 low. I would think a pulldown resistor between the base and ground would be in order. Maybe 10K? Might require some experimenting to find the correct value.

[mirocha]

I don't see anything that pulls the base of Q1 low. I would think a pulldown resistor between the base and ground would be in order. Maybe 10K? Might require some experimenting to find the correct value.

The circuit does work it is designed by Gecko drives, it works fine at 48 volts using a 48 VDC regulated power supply but when I upgraded to a 70 VDC unregulated power supply at the higher voltage Q1 shorts out and fries the 33 ohm resistor.

[Jim Dawson]

Changing from 48V to 70V proabaly requires a change of R2, you've increased the system voltage by about 1/3. Probably getting enough base current through R2 to switch Q1 on. R3 may also have to be changed to a higher value keep the dump current within the working range Q1.

EDIT: I just looked at the data sheet on the TIP147, it has built in pull down resistors. So just changing the value of R2 should fix the problem.

http://www.mouser.com/ds/2/149/TIP147T-890154.pdf

[mirocha]

The following is the circuit description from Gecko: CIRCUIT DESCRIPTION:

Normally power supply current flows thru rectifier D1, biasing Q2 off via R2. If the direction of current reverses, D1 shuts off and a reverse voltage develops across R1. This voltage now turns Q1 on. The returned current now flows from the drive, thru Q1 and to ground via R3. The main purpose of R3 is to keep Q3 within its secondary-breakdown limits (SOA).

I think Gecko meant to say Q1 instead of Q3 in the last sentence there is no Q3. Based on what you said and Gecko's circuit description I think your statement of " R3 may also have to be changed to a higher value keep the dump current within the working range Q1" may be what needs to be done not changing R2. I don't know how to calculate what I should change R3 to and buying and burning up resistor as trial and error is not a good way to do it.

If I am trying to keep Q1 within its secondary breakdown limits, maybe it would be good to also change out Q1 to a more robust transistor but again I would need to have someone tell me what would be a better darlington transistor to use and the R3 resistor value and wattage to use for either the TIP147 or for an upgraded transistor that has a higher breakdown limit. Perhaps there is a transistor that a limit that can still use the same R3 resistor if that's the problem. One of the things I am concerned with is the TIP147 has a voltage rating of 100 volts and I would think the back EMF could easily exceed the voltage rating of the TIP147. The circuit worked at 48 volts if the back EMF doubles that voltage and its still below the TIP147 rating but double the 70 volts and its 40 volts above the TIP147 voltage rating. I don't know how much voltage Back EMF produces but the way the transistor shorted out I don't know if its a current issue, voltage issue or both.

I need a recommendation on resistor value and if the TIP 147 is still viable at the higher voltage.

Thanks Joseph

Help please

Joseph

[john-100]

looking at the modded current dump circuit

when the returned energy rapidly increases the voltage across C1,
normally the TIP147 transistor connects the 33 ohm resistor across the capacitor C1 to disipate the excess energy

with the modification the second 1000uF & 1N4004 will effectively short circuit the 33 ohm resistor and
result in a larger current flowing through the transistor that could be damaging it

try adding a 10 ohm resistor in series with the 1N4004 diode to reduce the initial current that charges the added 1000uF capacitor



john

[mirocha]

looking at the modded current dump circuit

when the returned energy rapidly increases the voltage across C1,
normally the TIP147 transistor connects the 33 ohm resistor across the capacitor C1 to disipate the excess energy

with the modification the second 1000uF & 1N4004 will effectively short circuit the 33 ohm resistor and
result in a larger current flowing through the transistor that could be damaging it

try adding a 10 ohm resistor in series with the 1N4004 diode to reduce the initial current that charges the added 1000uF capacitor



john

I understand your point. This will in effect be parralling the two resistors which would be raising the resistance through Q1 to ground instantaneously lowering the current.
I am only looking to charge c2 to lite the LED with out c2 the LED only blinks quickly and that was when I tested it using the 48 vdc power supply. Now after your comments i think that 10 ohms may not be high enough to lower the initial current enough. How high of a resistor can i use and still charge c2 so that I minimize initial current on Q1 Do you think the TIP147 rated at 100 volts is ok for the higher 70 volt power supply?

[john-100]

when the TIP147 switches on ,
the 33 ohm resistor will initially will be in parallel with the 10 ohm resistor , plus the effective series resistance of the capacitor and the forward resistance of the 1N4004 (this is about 10 ohms not the 7.7 ohms of the 33ohm and 10 ohm resistors in parallel)
but rapidly increase to 33 ohm as the 1000uF capacitor (C2) is charged

as the TIP147 will be switched on as soon as the voltage across the driver supply terminals is around 2 V higher than the power supply output
I would expect the TIP collector at switch on will be about 7.5 A ( give or take a little , depending on the amount of returned energy )

as the diode D1 isolates the power supply as soon as the drivers supply terminals are 0.7V higher
the question is whats the off load voltage from your power supply ???
if its 80V the maximum voltage across the TIP147 will be about 82V


John

[mirocha]

when the TIP147 switches on ,
the 33 ohm resistor will initially will be in parallel with the 10 ohm resistor , plus the effective series resistance of the capacitor and the forward resistance of the 1N4004 (this is about 10 ohms not the 7.7 ohms of the 33ohm and 10 ohm resistors in parallel)
but rapidly increase to 33 ohm as the 1000uF capacitor (C2) is charged

as the TIP147 will be switched on as soon as the voltage across the driver supply terminals is around 2 V higher than the power supply output
I would expect the TIP collector at switch on will be about 7.5 A ( give or take a little , depending on the amount of returned energy )

as the diode D1 isolates the power supply as soon as the drivers supply terminals are 0.7V higher
the question is whats the off load voltage from your power supply ???
if its 80V the maximum voltage across the TIP147 will be about 82V


John

I have 6.8k 2 watt, 1k 1\2 watt and 150 ohm 1\2 watt resistors i would like to use what I have its Saturday I would like to use the 1k if you think it would work i have transistors and diodes so I can work on it now but if you think i need to use a 10 ohm I'll wait till I can get them, no radio shacks around here

[john-100]

if you have them , three or four 150 ohm resistors you can wire in parallel to give you 40 to 50 ohms could work instead of the 10 ohm resistor

alternatively , depending on the components you have , some thing like this could work if you have a 100V NPN transistor
and 100uF 100V capacitor


or


John

[mirocha]

I replaced the diodes and transistor in one of the blown return energy dump circuits, I left out what I added the diode, cap, led and resistor to try the original gecko circuit and after multiple tries it seems to work but with out the led there is no indication Q1 is turning on, but nothing smoked.

I will order the parts for your design of the circuit, one resistor you say to use a 22k to 100k resistor can you let me know which is best I will be ordering the parts so I may as well get what is best. Also for the NPN transistor I could get the complementary TIP 142 which is a NPN 100 volt rated, let me know which transistor I should order.

Thank you so much you, I will post once I get the parts and test it out.


Joseph

[john-100]

as its midnight I'll have another look at it in the morning and post any more thoughts I have

for the MPSA42 a base resistor any spare resistor between 22K & 100K should work
but I would probibly go for 47K if I bought parts for the project

John

[john-100]

now I have had another look , this is what I would build



the diode D1 has to carry the full load current to all the drivers connected to the circuit
so I would use a minimum of a 15A diode at least - a 20 or 25A diode could be better option

depending on your supplier , you may find it less expensive to use part of a bridge rectifier than a single diode !!!
connecting the two ac terminals of the bridge rectifier to the power supplies positive terminal
and connecting the bridge rectifiers positive terminal to the driver(s)

not knowing how long the TIP147 will be conducting
its not going to be possible to know if the capacitor C2 will be fully charge and therefor how long the LED will be ON

assuming C2 is charged to 80V , the 39K resistor (R5) limits the MPSA42's base current to 2mA

as C2 discharges , the MPSA42 will dissipate the most power when the collector to emitter resistance is equal to the 6K8 LED current limiting resistor
the dissipation at 80V will be 470 mW which is less than the maximum of 625 mW for the MPSA42

the diode D3 is optional and just speeds up the discharge of the capacitor C2
when the power is switched off

if you use a TIP142 Darlinton NPN transistor instead of a MPSA42 then you can increase the resistance of R5 the 39K resistor to 390K , since the TIP142 has a very large current gain

John

[mirocha]

now I have had another look , this is what I would build



the diode D1 has to carry the full load current to all the drivers connected to the circuit
so I would use a minimum of a 15A diode at least - a 20 or 25A diode could be better option

depending on your supplier , you may find it less expensive to use part of a bridge rectifier than a single diode !!!
connecting the two ac terminals of the bridge rectifier to the power supplies positive terminal
and connecting the bridge rectifiers positive terminal to the driver(s)

not knowing how long the TIP147 will be conducting
its not going to be possible to know if the capacitor C2 will be fully charge and therefor how long the LED will be ON

assuming C2 is charged to 80V , the 39K resistor (R5) limits the MPSA42's base current to 2mA

as C2 discharges , the MPSA42 will dissipate the most power when the collector to emitter resistance is equal to the 6K8 LED current limiting resistor
the dissipation at 80V will be 470 mW which is less than the maximum of 625 mW for the MPSA42

the diode D3 is optional and just speeds up the discharge of the capacitor C2
when the power is switched off

if you use a TIP142 Darlinton NPN transistor instead of a MPSA42 then you can increase the resistance of R5 the 39K resistor to 390K , since the TIP142 has a very large current gain

John

I am using a separate energy dump circuit for each gecko drive, the stepper motor current will be limited to 3.5 amps by the gecko drive, so I believe D1 will be ok it is rated for 10 amps. There are several reasons to have a separate energy dump circuit for each drive, lower current and with each having the LED it let me see each drive seperatly.

I will use the TIP142.

Let me know if D1 is ok for just one drive, I will be using a separate circuit for each drive.

Thanks again

Joseph

[john-100]

one circuit per drive is a detail I did not have (may be I missed it last night )
with a separate energy dump circuit for each gecko drive the 10A10 diode will be OK



john

[mirocha]

one circuit per drive is a detail I did not have (may be I missed it last night )
with a separate energy dump circuit for each gecko drive the 10A10 diode will be OK



john

I ordered the parts today to build your design, I am making 6 of them, cost about $10 US each.

Thanks Joseph

[mirocha]

I ordered the parts today to build your design, I am making 6 of them, cost about $10 US each.

Thanks Joseph

Built one circuit to test design. The very first time the stepper motor stopped quickly the LED on the Returned Energy Dump Circuit lit and stayed lit and the 33 ohm resistor started to smoke. This is telling me the TIP 147 is staying on or is shorted. I did use the TIP142 and the 390K resistor and did not use the D3 optional diode. Is the 100uf cap to much added load to the TIP 147, maybe the 100uf cap should be on the other side of the TIP142 somewhere or different resistors?

[mirocha]

Built one circuit to test design. The very first time the stepper motor stopped quickly the LED on the Returned Energy Dump Circuit lit and stayed lit and the 33 ohm resistor started to smoke. This is telling me the TIP 147 is staying on or is shorted. I did use the TIP142 and the 390K resistor and did not use the D3 optional diode. Is the 100uf cap to much added load to the TIP 147, maybe the 100uf cap should be on the other side of the TIP142 somewhere or different resistors?

I don't know maybe I bought bad transistor any thoughts?

[TomKerekes]

Hi Joseph,

I wonder if the circuit is breaking into oscillation. Do you have a scope? When the transistor switches on if the supply wiring is long and has any inductance the input voltage may drop making the circuit think more clamping is needed, etc... Or something like that. You might try adding a filter capacitor on the input. Such as a 0.1uF 100V ceramic capacitor. Also possibly the output. Although the output already has a huge capacitor such a capacitor has too much inductance to be effective at high frequencies.

Regards

[mirocha]

Hi Joseph,

I wonder if the circuit is breaking into oscillation. Do you have a scope? When the transistor switches on if the supply wiring is long and has any inductance the input voltage may drop making the circuit think more clamping is needed, etc... Or something like that. You might try adding a filter capacitor on the input. Such as a 0.1uF 100V ceramic capacitor. Also possibly the output. Although the output already has a huge capacitor such a capacitor has too much inductance to be effective at high frequencies.

Regards

Back to basics, tried the Gecko return energy dump circuit with only adding a 6.8K resistor and an LED as below. Tried it numerous times with the upgraded 70 volt 800 watt power supply and it worked with no problems. The LED flashes when the stepper motor is coming to a quick stop. The LED flashes bright and long enough to see with no problem. This let me know the TIP 147 transistor is turning on and the circuit is working. In my trial and error method I did find out that if the 1000uf cap is bad the circuit will not lite the LED so it also lets me know that the cap is ok by lighting.

The unit that is working is using a STMicroelectronics TIP147 transistor. I made a second unit using the new TIP147 transistors I bought from China, an off brand and the circuit/transistor failed on the first try and fried the 33 ohm resistor.

I ordered STMicroelectronics TIP 147 transistors from Digikey and should have them next week, I am now thinking the chinese transistors I bought are all bad and that is what caused the more complicated circuit with the 100uf cap to fail, I used the cheap China transistors.

Gecko return energy dump circuit with only adding a 6.8K resistor and an LED is actually very nice and I will stick with that design, it works and does what I need it to do, I would have liked to get the LED to stay on a little longer with a capacitor but the added load of the capacitor on the STMicroelectronics TIP 147 fried it and the other circuit with the 100uf circuit failed because of the Chinese transistors and I'm done with trying to get that to work. I could try it with the STMicroelectronics TIP 147 but at this point I don't see any real benefit.

The TIP 147 is rated at 100 volts 10 amps which I think is a little close to what the circuit is and would like to change the TIP 147 to a higher rated transistor. What I found was a MJH11019 that is rated at 200 volts and 15 amps. I don't know if that would work because the TIP 147 has built in Base-Emitter shunt resistors which the MJH11019 does not have, I don't know if it would work as a drop in replacement and I don't know how I would build an external Base-Emitter shunt.

Below is the circuit that worked numerous times using a STMicroelectronics TIP147 transistor, however with the issues I have had, it needs to be verified that the 6.8k resistor and LED combination and the way it is hooked up in the circuit is proper at 70VDC.
I will try the new STMicroelectronics TIP147 transistors but if someone can tell me that the MJH11019 transistor would work I would use it for the higher rating.