Old circuit needs to be re-born Smaller

[ccurtis]

Tanker, armed now with the knowledge from one of your previous posts that the output of the T1 is purely on-off, this device has all four transistors in the circuit you are presently building in one package. This makes the buffer smaller and easier to put together. It will still need to be attached to metal to provide heat sinking.

https://www.semicon.toshiba.co.jp/docs/datasheet/en/LinearIC/TA7267BP_en_datasheet_070228.pdf

 

[ccurtis]

Tanker, armed with the knowledge from one of your previous posts that the output is on/off, the IC at the link below combines the bridge circuit transistors in one IC and should interface directly to the T1. Of course, mounting to the engine metal should be done to dissipate heat.

https://www.semicon.toshiba.co.jp/docs/datasheet/en/LinearIC/TA7267BP_en_datasheet_070228.pdf

 

[Tanker135E]

Ok I have a couple of these on order. When they come in I will try them out. It looks like it an easy wire but who knows till I try. steve

 

[Tanker135E]

Ok Chuck I have the time and items to try this out. I think I have it correct but check it out for me.pins 6,7 get power from either the track or pins 6+8 from T-1, then pins 1,2 get the signal from T-1 orange and brownwires and pins 3,5 go to the motor/train. Question is since the pins6,8 on the throttle(T-1) were intended for the lamp on the train engine, might I be overloading the T-1 taking power from here? Maybe the trace for pins 6,8 can't handle 1amp, since it was design for a grain of wheat bulb which draws 30ma? The intent here was to protect the non replaceable T-1. I don't want to burn one up playing around! I will give it a shot running it threw its own BR first. steve

 

[ccurtis]

Ok Chuck I have the time and items to try this out. I think I have it correct but check it out for me.pins 6,7 get power from either the track or pins 6+8 from T-1, then pins 1,2 get the signal from T-1 orange and brownwires and pins 3,5 go to the motor/train. Question is since the pins6,8 on the throttle(T-1) were intended for the lamp on the train engine, might I be overloading the T-1 taking power from here? Maybe the trace for pins 6,8 can't handle 1amp, since it was design for a grain of wheat bulb which draws 30ma? The intent here was to protect the non replaceable T-1. I don't want to burn one up playing around! I will give it a shot running it threw its own BR first. steve

Hi Steve. The traces would have to be unusually thin not to handle 1A. I don't know if you can see the traces, but if you can, measure how wide they are and let me know. The T1's BR should handle the motor since that is what it did without the added bridge. Unless it was the BR that was getting damaged all this time, I would not be concerned with burning out the BR. Do you know what part in the T1 was getting destroyed? By the way, I am curious just exactly what part was getting destroyed in the T1. Also, is the T1 repairable? I may have asked that, but I don't remember.

Anyway, your connections are correct if I understand you correctly. To be sure, if getting power from the T1, connect pins 6&7 of the bridge IC to pin 8 of the T1. Connect pin 4 of the bridge IC to pin 6 of the T1. Connect pins 3 and 5 of the bridge IC to the motor. Connect pin 1 of the bridge IC to pin 3 of the T1. Connect pin 5 of the bridge IC to pin 4 of the T1. You will have to reverse the wires going to the motor if the direction of movement is not what you expect.

You can try with a separate BR, but make sure the - side of the BR gets connected to pin 4 of the IC and pin 6&7 of the IC go to the + side of the BR.

 

[Tanker135E]

Chuck The T-1 was being damaged by heat, so I am not sure which components failed? This little H-bridge (booster) actually a amplifier makes the T-1 a pre amp and reduces the T-1 to a constant 1/10 amp irrespective of the motor current or load, thus the T-1 runs cold. I assume that the L293 in the T-1 which I believe to be the output stage failed,conversely the smaller T-1/2 throttles L272 failed as well. Rarely did any of the 2 or 4 amp throttles fail as they never developed the rated amps, and were located in a larger type train with more air flowing!. The designer of the booster states that you could run one T-1 and 4 boosters to run 4 motors and still only draw 1/10 amp from the T-1 steve

 

[Tanker135E]

Chuck, I gave it a try tonight and came up with nothing. That means it did nothing No fwd No rev No heat in either the T-1 or the IC. I recheck and everything check where it was supposed to be. Only thought was the input wires might have been oposite the T-1's which could have fried the IC? I did take it all apart and tryed the T-1 on its own and it worked ok. Tomorrow I will try to use a new IC and make sure I get the polarity correct!
steve

 

[ccurtis]

Sorry to hear that, Steve. The input wires reversed should only have resulted in the motor going backwards when it was commanded to go forward. I would try powering the IC off the T1 pins 6 and 8 instead of a separate BR.

 

[ccurtis]

Steve, I made the attached connection diagram so there is no mistaking the connections. One diagram is with a separate bridge rectifier and the other is without.

 

[Tanker135E]

Chuck I miss the ground pin 4 I put the input wires one to 6 and one to 7. Not one to 6&7 and one to 4. The whole think had no ground. I get back to you alter today. steve

 

[Tanker135E]

Chuck with it rewire correctly it works. But it had very erratic control. Each input of control to the motor resulted in the motor going from running to stopped then to the next higher or lower speed which ever was selected. I put a 4.7uf 35v cap. across the motor brushes, that smoothed it out completely. However I am not seeing any decrease in temp on the T-1? I am going to give it a workout on the bench over the next few days and see if I see results. As a note the T-1 runs around 140 F to 155 F while in operation. With the first H bridge the T-1 Ran cool and the H bridge ran around 160 F. Today's test had the T-1 running around 115 F - 125 F and the TA7267BP running at
72 F. I have to put the T-1 under load to see what happens. steve

 

[ccurtis]

Steve, good idea adding the capacitor. It is very odd the T1 runs hot at all. The TA7267BP consumes virtually no power from whatever drives its inputs (pins 1 and 2); input current consumption is in the microamp range. When you measure 140-155 F on the T1, at what component on the T1 are are you taking this measurement, exactly? Does the T1 run hot even when the motor is commanded to off and just sitting there for a long while with the TA7267BP and everything connected?

It's worth a try taking power for the TA7267BP from the T1 as shown in the bottom diagram I posted since the T1's internal bridge recifier is not the component in the T1 that goes bad from what you said. Though, I dont see that using an external bridge recifier as a reason for the T1 running hot.

 

[Tanker135E]

Chuck I used the T-1 as the BR, did not used outside source. Looked like the heat was coming from either one or two of the power transistors or one of the two rectifier diodes on the T-1 and some resistors next to it. I did a quick Amp check and it showed a .200ma on either number 3/4 wires going to TA7267BP this was the old set of wires that use to go to the motor. Amp meter on my control panel was reading about .500ma at about 3/4 speed. So that says that its now drawing less amps (T-1) the T-1 draws about 100ma sitting at rest. Note the track power is 15.62v and after going threw the BR on T-1 it is 14.20 I wasn't thinking the TA7267BP was causing the draw/heat but was expecting it to be hot not the T-1. I did check another T-1 in service and it was running about 130 after just a few minutes of running, it was just a T-1 without any external components.
steve

 

[ccurtis]

I did a quick Amp check and it showed a .200ma on either number 3/4 wires going to TA7267BP this was the old set of wires that use to go to the motor.

That's 3000 times less current than the motor would use. Looking at the datasheet for the TA7267BP that's about right with boths inputs (3/4 wires) at 14.2 volts.

Note the track power is 15.62v and after going threw the BR on T-1 it is 14.20

That's expected, as a bridge rectifier will drop about 1.4 volts (15.62-1.4=14.22).

I wasn't thinking the TA7267BP was causing the draw/heat but was expecting it to be hot not the T-1.

The TA7267BP won't consume as much power, as the transistors in it are acting as on/off switches. So, it shouldn't get very hot. The hottest it will get is when the motor is set to run about half throttle. The transistors in the "H-bridge" you have been building are connected as emitter followers, not as on/off switches, so I expect they will run hotter than the TA7267BP will.

I did check another T-1 in service and it was running about 130 after just a few minutes of running, it was just a T-1 without any external components.

I don't quit understand why the T1 should get that hot without any load applied (though, that is not very hot). Maybe the output device that would drive the motor is running class A. It is what it is, as they say.

 

[Tanker135E]

Chuck, my buddy who is my life saver when it comes to this stuff, says the last page of the data sheet eludes to this ossalation I got when first hooked it up. He thinks it needs resistors across ?? Not at the motor directly? said that the TA7267BP is treating the Motor as just a simple DC motor when the T-1 is not. I think because its sending pulses? I know more when he gets here. steve

 

[ccurtis]

Steve: Yes, the data sheet indicates putting a small value resistor is series with the capacitor across the motor, but I thought things are operating well now? The rather large capacitor you are using is going to have a enough ESR without adding a small value resistor in series. I realize the T1 is sending pulses, but also think that the TA7267BP can accommodate them.

 

[Tanker135E]

Chuck I am not sure what w did tonight but we spent 4 hrs working on it. We used its own BR and it worked but the T-1 was getting hot. At some point we were able to get it working with the T-1 running 80F degrees and 1/10 amp but the motor only would run about half speed when the T-1 was commanding full. We try a new IC and got the same results. We finally fried the T-1 i wil try to look at in tomorrow. steve

 

[ccurtis]

Ah, bummer Steve. The whole point of the output buffer is to prevent burning up T1s. I don't understand why the T1 would get hot. The TA7267BP draws hardly any power from the T1, no matter what.

I have only the schematic for the T1 you supplied to work with. Something tells me there's more to the system than meets the eye.

 

[Tanker135E]

Chuck I am going to see if i can get you some more info. We did put the T-1 on the scope and it has purely Digital out put. We ran two T-1's side by side one with the TA7267BP one without. My buddy was scratching his head as to why the loss of volts thru theTA7267BP
steve