Using 12V relays on 15V to "ensure fast and reliable closing" is a remarkable approach. Those 12V relays are designed to work on 12V with a margin on the lower and on the upper side. They already pick up at 9V and should be reliable at 12V as that is... eh the voltage they're designed for. They indeed pick up marginally faster (0,3 ms) at 15V but who needs that in this application and is the difference noticeable ? Please let us use components as they're intended to be used. Please realize that unexperienced builders might get wrong impressions of such examples.
http://pewa.panasonic.com/pcsd/product/sign/pdf/mech_eng_tq.pdf
About the transformer: I use a 2 x 12V 5VA toroid with no problems whatsoever and 12V relays. Result is a Mezmerize that is very small, reliable, cool and green. It gives 2 x 14V AC with this load and I have more than 8V voltage drop across the shunt supplies. I dare to say that it is the smallest Mezmerize on the planet
with this small 5VA transformer, this mez setup could actually benefit from the 24V relays as the current draw would be lower by a few mA, both in the relays and the 7812 itself.
Good point but I am not the one having 24V relays The 12V version is also not very power hungry with its 12 mA !
However, I would buy a 7VA toroid next time if I wouldn't use such a small case. The current case is 240 x 150 x 65 mm. I finished a Mez this weekend and used the same type of 5VA as I had it in stock. Bragging alarm !!!! ->>>> This time I ended up with -0.2 mV and -0.7 mV offset which IMO is extremely low.
The 12V version is also not very power hungry with its 12 mA !However, I would buy a 7VA toroid next time if I wouldn't use such a small case. The current case is 240 x 150 x 65 mm. I finished a Mez this weekend and used the same type of 5VA as I had it in stock. Bragging alarm !!!! ->>>> This time I ended up with -0.2 mV and -0.7 mV offset which IMO is extremely low.
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Good point but I am not the one having 24V relays
However, I would buy a 7VA toroid next time if I wouldn't use such a small case. The current case is 240 x 150 x 65 mm. I finished a Mez this weekend and used the same type of 5VA as I had it in stock. Bragging alarm !!!! ->>>> This time I ended up with -0.2 mV and -0.7 mV offset which IMO is extremely low.
with such a small xfmr, what is the current source setting of the shunt regulators?
Of course the original setting, 60 mA. Hotrodding is not my thing and it is impossible in this situation too. The 5VA toroid can deliver 200 mA continuously. The 2 relays that are normally both on only take 24 mA in total. The power LED is a low current type which burns at 1 to 2 mA so the 2k2 is now a 4k7. The toroid does not even get lukewarm after hours of use and it delivers 2 x 14V with this light load. The filter caps are 6800/25.
Yeah, I know the "headroom" doesn't feel very large but in practice and calculated it is enough. I used to over-dimension everything and a few years ago I would have used a 30 or 50 VA but it is useless when the power is not needed. Too big, too heavy, too expensive.
Again, next time I would use a 7 or 10VA to keep my conscience at rest. The 7VA is only 4 mm higher and not wider so I could have chosen that one.
Yeah, I know the "headroom" doesn't feel very large but in practice and calculated it is enough. I used to over-dimension everything and a few years ago I would have used a 30 or 50 VA but it is useless when the power is not needed. Too big, too heavy, too expensive.
Again, next time I would use a 7 or 10VA to keep my conscience at rest. The 7VA is only 4 mm higher and not wider so I could have chosen that one.
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a 10VA 12+12Vac transformer can supply a maximum continuous AC current of 416mAac........ the BOM is over-stating the transformer spec?
When feeding a capacitor input filter the output must be de-rated by the manufacturer's DR factor. I usually use 70%.
This reduces the maximum continuous DC current to ~half the AC current limit.
Expect the transformer to run pretty warm when maximum continuous output = 208mAdc.
Many builders recommend that a transformer be run in continuous duty at <=50% of maximum rating.
This recommendation for cooler running and long-term reliability comes out at 104mAdc continuous from the 10VA 12+12Vac transformer.
One Hypnotize runs 60mA + control current into the audio regulator.
The relay side pulls another 10 to 25mA per activated relay. There is only one relay so the continuous DC current is ~45% of maximum rating when using a 5V relay. Should run forever without reliability problems.
A Mezmerize has two relays activated.
A 12V relay version pulls about the same current as a 5V Hyp.
This again is OK.
A 5V Mez would run the transformer @ ~54% of maximum rating, again OK, because this continuous current is ~half the maximum continuous rating.
If you up the transformer to 15+15Vac you must also increase the VA rating to maintain similar current loading vs current rating. A 10VA will run a bit warm, a 12VA will run slightly cooler, I would be tempted to use >=15VA 15+15Vac for a 5V MEZ.
If any experiments with higher currents are expected then use a higher VA rated transformer. It is not excessive. It is necessary.
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@jean-paul: are you saying that the BOM is over-stating the transformer spec?
Yes, you can use a 10VA easily. For clarity: we are talking about a non hotrodded situation so with 2 x 68 Ohm resistors in the shunt supply. Derating factor is considered 1.8 x DC current by most transformer manufacturers. I say deliberately "transformer manufacturers" as those are the guys that produce this stuff so they should know what their products are capable of. What many builders do is their business. Mez does not take more than 100 mA DC (in fact far less but it is better to keep some play) in total so 1.8 x 100 mA = 180 mA at the AC side.
Tight indeed with a 5VA but still within limits as proven. I would recommend a 10VA or larger though.
edit: I just measured the situation and it takes less than 73 mA at each 12V AC side with no input signal applied and 2 TQ2-12V relays activated. With 3 relays it goes to 80 mA after the relays have been activated. I did not exaggerate and 5VA is adequate (for me).
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Really? Shunts alone are sucking 60mA per side, so a mez would consume 120mA JUST in the shunts. Where do these 100mA come from?
60mA per side (polarity) is still 60mA. They do not add up to make 120mA.
mez power calculation
for transformer with 12V x2 secondaries
negative rail draws ~65mADC x 18VDC = 1.17W (60mA in shunt, 5mA Vref)
positive rail draws ~126mADC x 18VDC = 2.27W (60mA in shunt, 5mA Vref, 5mA 7812, 2 relays @ 28mA per relay for 5V Pana TQ2's)
total power DC power dissipation is 3.44W
derating for AC to DC on xfmr, 3.44 X 1.8 = 6.19 VA,
so the 5VA transformer is a bit undersized when using the 5V relays, with 7VA or 10VA being a recommendation instead.
for transformer with 12V x2 secondaries
negative rail draws ~65mADC x 18VDC = 1.17W (60mA in shunt, 5mA Vref)
positive rail draws ~126mADC x 18VDC = 2.27W (60mA in shunt, 5mA Vref, 5mA 7812, 2 relays @ 28mA per relay for 5V Pana TQ2's)
total power DC power dissipation is 3.44W
derating for AC to DC on xfmr, 3.44 X 1.8 = 6.19 VA,
so the 5VA transformer is a bit undersized when using the 5V relays, with 7VA or 10VA being a recommendation instead.
Sorry jean, my eyesight wasn't at it's best
Aha, it was the Rioja !
Again, I am using 12V relays and not 5V nor 24V relays. Why use other relays than 12V types when using a 7812 reg anyway ? Since it is already a mA calculation derby I would not challenge fate by using other than 12V relays. It must be difficult to read as I posted the measurements earlier. The total device draws 73 mA at both AC sides with 2 pieces of TQ2-12V relays active using a transformer that is guaranteed to supply 200 mA at each side continuously. Not much headroom with a 5VA but a 7VA or 10VA would have some more breath... Only a person ,well, without common sense would use a small transformer AND 5V relays.
But you are right: when using a 5VA 2 x 12V transformer using 5V relays is not wise. BTW I think you forgot to add the current through the 2 JFETS x 2 ...
OK, OK, I will admit. Please use 300VA or 500 VA transformers that are heavy and look good to supply 73 mA or 0.073 A and it will also sound better
Let's stop this useless discussion please.
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Aha, it was the Rioja !
Again, I am using 12V relays and not 5V nor 24V relays. Why use other relays than 12V types when using a 7812 reg anyway ? Since it is already a mA calculation derby I would not challenge fate by using other than 12V relays. It must be difficult to read as I posted the measurements earlier. The total device draws 73 mA at both AC sides with 2 pieces of TQ2-12V relays active using a transformer that is guaranteed to supply 200 mA at each side continuously. Not much headroom with a 5VA but a 7VA or 10VA would have some more breath... Only a person ,well, without common sense would use a small transformer AND 5V relays.
But you are right: when using a 5VA 2 x 12V transformer using 5V relays is not wise. BTW I think you forgot to add the current through the 2 JFETS x 2 ...
OK, OK, I will admit. Please use 300VA or 500 VA transformers that are heavy and look good to supply 73 mA or 0.073 A and it will also sound better
yes, i forgot that you are using the 12V relays, not the old 5V types. just killing some time while new Mez group buy waits for more orders...
by the way, totally unrelated to this thread, I have old Philips CD50 (TDA1541 based) that became erratic after I tried to "improve" it by recapping, etc. Maybe you could direct me to some threads about this-- its running in overspeed when I power it on now, and FL display looks a bit strange...
Erratum: when I was busy with my last Mez today I remeasured currents, offset etc. My eye fell on the toroid when adding a fused connector and to my surprise I have used 7VA types. I have bought them as 5VA types some time ago but they are 7VA in reality ( 2 x 12V 0.292 mA type 60032). Sorry for any confusion I might have created.
These are Talema/Nuvotem type 60032 2 x 12V 0.292 mA. At RS they have the RS stocknummer 278-6986. They stay cool and don't make any noise.
These are Talema/Nuvotem type 60032 2 x 12V 0.292 mA. At RS they have the RS stocknummer 278-6986. They stay cool and don't make any noise.
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