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[BoyntonStu]

I mount a MS16a directly on a TM751.

A thought occurred to me; why not use dc tapped from the 751 for a trickle charger for NiCd batteries in the MS16?

Has anyone played around inside a 751 and measured volts?

[Brian H]

TM751 uses a power line derived supply.
Would be a very dangerous external connection as it could be at power line voltages with reference to ground. That is also why the external antenna is not directly connected to the receiver in the TM751.

New version units have a +5 volt supply but knowing X10 there isn't an extra milliamp of excess current available for anything.

I believe the raw supply was around 40 volts for the power line transmissions. It is not in my notes so this is from memory. 

Older units before the new surface mounted controller was used. Is +19 volts.

[JeffVolp]

The TM751 has a transformerless power supply referenced directly to the powerline.  It is dangerous to make any electrical connection to the internals unless you know exactly what you are doing.

I don't have a schematic for the TM751, but it is probably similar to the RR501.  The raw supplies for that unit are +/- 19V.  Transformerless supplies cannot deliver much current, but you might be able to steal a couple of milliamps from the negative supply.

Jeff

[Brian H]

Stu; Since yours are a recent purchase. They would be newer than my Date Code 08D14 and it has the surface mounted controller.
The Common Power Supply connection is the Power Line Hot! That would put your supplies at around 120 volts AC ground..

Your best interest would be not to try it.

[BoyntonStu]

Stu; Since yours are a recent purchase. They would be newer than my Date Code 08D14 and it has the surface mounted controller.
The Common Power Supply connection is the Power Line Hot! That would put your supplies at around 120 volts AC ground..

Your best interest would be not to try it.

Close but no cigar?

A few measly ma at 3VDC  is not a major requirement.

Is it possible to wire it and seal it closed?

[Brian H]

Jeff; The new TM751 with surface mounted controller uses a single ended supply.
Common is power line hot.
Raw DC on C5 is around 43 volts with - on the common buss.
+5 is used for both the controller IC and the receiver board that now uses the same Himark IC as the CM15A does.
A schematic I found on line for the older version shows a +19 volt supply and a 78L05 on the receiver board for +5 where needed.

I have also seen different RR501 schematics.
One has the -19 and +5 supplies separate as you mentioned.
One has a +19 volt supply and a 78L05 on the +19 volts for the +5.

[Brian H]

I am not concerned with the 3 ma.
I am more worried about an unsafe condition.

[JeffVolp]

Jeff; The new TM751 with surface mounted controller uses a single ended supply.
Common is power line hot.
Raw DC on C5 is around 43 volts with - on the common buss.
+5 is used for both the controller IC and the receiver board that now uses the same Himark IC as the CM15A does.
A schematic I found on line for the older version shows a +19 volt supply and a 78L05 on the receiver board for +5 where needed.

I have also seen different RR501 schematics.
One has the -19 and +5 supplies separate as you mentioned.
One has a +19 volt supply and a 78L05 on the +19 volts for the +5.

It looks like they simplified the supply to make it a little cheaper to build.  Like you said, the schematic I have derives 12V and 5V off the raw positive supply.  It looks like those feed most of the circuitry, so the positive supply is probably heavily loaded.  The only load I saw on the negative supply was the transmitter, so that should have some current to spare most of the time.  The single supply version must also have some excess capacity to power the transmitter.  Using the right series combination of a zener and dropping resistor to trickle charge the battery could pretty much remove that load during transmission.

Jeff

[BoyntonStu]

I am not concerned with the 3 ma.
I am more worried about an unsafe condition.

Safety is prime, I agree.

If you consider the 751 and the MS16 as a sealed plug in unit that must be unplugged for servicing, does that change the equation?

Take a lead off the +5 VDC, add a current limiting and voltage drop resistor and you have a 3 V DC charger.

Would a zener be necessary?

If 2 leads from the 751 are brought into the MA16 battery compartment and soldered to the +- terminals, what is the danger to a person who unplugs the unit in order to replace the NiCd batteries?

[JeffVolp]

Take a lead off the +5 VDC, add a current limiting and voltage drop resistor and you have a 3 V DC charger.

Would a zener be necessary?

As you probably know, adequate X10 signal levels are often an issue.  Transformerless supplies use a shunt regulator to clamp the maximum voltage.  The supply in the TW523 I tested several years ago had significant droop when the transmitter was active.  While I have not performed a similar test on the TM751, its supply probably also droops when transmitting.  Using a combination of a zener to drop most of the voltage, and a resistor to set the maximum charging current, the charger load would be effectively disconnected as the power supply droops due to the extra transmitter load.  As a result, the transmitter power would not be impacted.

Jeff

[BoyntonStu]

Take a lead off the +5 VDC, add a current limiting and voltage drop resistor and you have a 3 V DC charger.

Would a zener be necessary?

As you probably know, adequate X10 signal levels are often an issue.  Transformerless supplies use a shunt regulator to clamp the maximum voltage.  The supply in the TW523 I tested several years ago had significant droop when the transmitter was active.  While I have not performed a similar test on the TM751, its supply probably also droops when transmitting.  Using a combination of a zener to drop most of the voltage, and a resistor to set the maximum charging current, the charger load would be effectively disconnected as the power supply droops due to the extra transmitter load.  As a result, the transmitter power would not be impacted.

Jeff

My sensor is in contact with the 751 so range may not be an issue.

However, there is another BIG problem, UL approval of a 110 VAC product.

I wish that X10 would make 3 VDC available in for a jack or else make a combination transceiver/detector with charger.

I had better forget about it except for my home unit. 

[Brian H]

That maybe a wise choice.
Using it only on an educational test unit only.