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Using an AC-to-AC wall wart transformer/adapter in reverse
Suppose I have a plug-in transformer that reduces 120VAC power to some
lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. |
Using an AC-to-AC wall wart transformer/adapter in reverse
"Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you attached 12 volts to the line side of the transformer, you'd get 1.2 volts out. You'd want to go the other way to step up , but there are other considerations, such as the wattage you need the transformer to produce and what the wall wart is capable of producing |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 17:23:32 -0600, Matt
wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you do as you say, you'll get 1.2 volts output. You need a step up transformer. |
Using an AC-to-AC wall wart transformer/adapter in reverse
RBM wrote:
"Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you attached 12 volts to the line side of the transformer, you'd get 1.2 volts out. You'd want to go the other way to step up , but there are other considerations, such as the wattage you need the transformer to produce and what the wall wart is capable of producing Whoops, sorry. You and Phisherman are right. I meant to ask what voltage I would get at the prongs if I hook low AC voltage to what is normally the output. |
Using an AC-to-AC wall wart transformer/adapter in reverse
"Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If it is an AC output and not a DC output wall wart then you can connect 12 volts to it and get out about 120 volts if it is normally a 12 volt output. Just put the 12 volts to the normal 12 volt output and the prongs will have 120 volts on them . You have to check to see how much current or how many watts the transformer is rated for as not to overload it. If your wall wart is good for 12 volts at one amp, then about all you can draw at 120 volts is 1/10 of an amp. Usuallly transformers do not care if they are connected up either way. Sometimes the output voltage will exceed the insulation of the wiring. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 18:49:25 -0500, Phisherman wrote:
On Sat, 07 Feb 2009 17:23:32 -0600, Matt wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you do as you say, you'll get 1.2 volts output. You need a step up transformer. He'd get 120vac because he'd connect the 24VAC to the 24VAC side. The problem is going to be loses and power considerations. He'll be lucky if he ends up with enough power to run a clock. |
Using an AC-to-AC wall wart transformer/adapter in reverse
Ralph Mowery wrote:
"Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If it is an AC output and not a DC output wall wart then you can connect 12 volts to it and get out about 120 volts if it is normally a 12 volt output. Just put the 12 volts to the normal 12 volt output and the prongs will have 120 volts on them . You have to check to see how much current or how many watts the transformer is rated for as not to overload it. If your wall wart is good for 12 volts at one amp, then about all you can draw at 120 volts is 1/10 of an amp. Usuallly transformers do not care if they are connected up either way. Sometimes the output voltage will exceed the insulation of the wiring. Thanks. I am measuring about 25.7 VAC at the output when the input is 117.5 VAC. The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz 35W, Output: AC 24VCT 700 mA". So it is producing well over its nominal voltage. Can I conclude that it is unregulated---that it is just a plain old transformer? Can I expect the same _power_ capabilities in normal and reverse direction? Your remark about current seems to indicate that. It has a 3-prong (grounded) plug. What could that tell somebody about its innards? |
Using an AC-to-AC wall wart transformer/adapter in reverse
AZ Nomad wrote:
On Sat, 07 Feb 2009 18:49:25 -0500, Phisherman wrote: On Sat, 07 Feb 2009 17:23:32 -0600, Matt wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you do as you say, you'll get 1.2 volts output. You need a step up transformer. He'd get 120vac because he'd connect the 24VAC to the 24VAC side. The problem is going to be loses and power considerations. He'll be lucky if he ends up with enough power to run a clock. Why wouldn't the efficiency and power rating be about the same in both directions? |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 18:36:57 -0600, Matt wrote:
AZ Nomad wrote: On Sat, 07 Feb 2009 18:49:25 -0500, Phisherman wrote: On Sat, 07 Feb 2009 17:23:32 -0600, Matt wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you do as you say, you'll get 1.2 volts output. You need a step up transformer. He'd get 120vac because he'd connect the 24VAC to the 24VAC side. The problem is going to be loses and power considerations. He'll be lucky if he ends up with enough power to run a clock. Why wouldn't the efficiency and power rating be about the same in both directions? transformers aren't perfect. there are always loses. a 24VAC transformer will most likely really be a 30vac transformer with the understanding that there'll be 6vac of loses in the winding when a load is put on it. Connect 24vac to the secondary of what really is a 30vac transformer, and you'll get 96 volts and only when there is no load whatsoever. Put even a small load on it and you'll be lucky if you get 80 volts. The voltage drop on any part of the circuit is equal to the resistance times current (E=IR). |
Using an AC-to-AC wall wart transformer/adapter in reverse
Matt wrote:
Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If it is an AC output and not a DC output wall wart then you can connect 12 volts to it and get out about 120 volts if it is normally a 12 volt output. Just put the 12 volts to the normal 12 volt output and the prongs will have 120 volts on them . You have to check to see how much current or how many watts the transformer is rated for as not to overload it. If your wall wart is good for 12 volts at one amp, then about all you can draw at 120 volts is 1/10 of an amp. Usuallly transformers do not care if they are connected up either way. Sometimes the output voltage will exceed the insulation of the wiring. Thanks. I am measuring about 25.7 VAC at the output when the input is 117.5 VAC. The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz 35W, Output: AC 24VCT 700 mA". So it is producing well over its nominal voltage. Can I conclude that it is unregulated---that it is just a plain old transformer? Can I expect the same _power_ capabilities in normal and reverse direction? Your remark about current seems to indicate that. It has a 3-prong (grounded) plug. What could that tell somebody about its innards? It is very likely just a transformer; i.e., does not provide any sort of voltage regulation. A transformer may be operated in either direction - either winding can be used as the input. Don't exceed the voltage or current ratings of either winding. It is not necessarily true that the center tap on the 24V winding is rated for 700ma, but it probably is. The ground is probably connected to the transformer core. It might also ground the center tap of the 24V winding. Why not use your ohmmeter or a battery and bulb (sigh, LED) tester to find out? |
Using an AC-to-AC wall wart transformer/adapter in reverse
"Matt" wrote in message ... .. I am measuring about 25.7 VAC at the output when the input is 117.5 VAC. The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz 35W, Output: AC 24VCT 700 mA". So it is producing well over its nominal voltage. Can I conclude that it is unregulated---that it is just a plain old transformer? Can I expect the same _power_ capabilities in normal and reverse direction? Your remark about current seems to indicate that. It has a 3-prong (grounded) plug. What could that tell somebody about its innards? The ground plug is probably connected to the frame of the transformer or maybe not even connected at all. As I mentioned , within limits a transformer can be used either way. As yours is rated for 35 watts, you can get 24 volts out at 700 ma or 7/10 of an amp. The 24 volts and 700 ma is only abuot 16.8 watts. If connected in reverse the best you can do is get around 120 volts out at about .14 amps. Not too much you could power with that. Most wall warts are not too efficiant and the voltage will probably drop a good percentage with a load on them over the no load condition. |
Using an AC-to-AC wall wart transformer/adapter in reverse
"Matt" wrote in message ... Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If it is an AC output and not a DC output wall wart then you can connect 12 volts to it and get out about 120 volts if it is normally a 12 volt output. Just put the 12 volts to the normal 12 volt output and the prongs will have 120 volts on them . You have to check to see how much current or how many watts the transformer is rated for as not to overload it. If your wall wart is good for 12 volts at one amp, then about all you can draw at 120 volts is 1/10 of an amp. Usuallly transformers do not care if they are connected up either way. Sometimes the output voltage will exceed the insulation of the wiring. Thanks. I am measuring about 25.7 VAC at the output when the input is 117.5 VAC. The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz 35W, Output: AC 24VCT 700 mA". So it is producing well over its nominal voltage. Can I conclude that it is unregulated---that it is just a plain old transformer? Can I expect the same _power_ capabilities in normal and reverse direction? Your remark about current seems to indicate that. It has a 3-prong (grounded) plug. What could that tell somebody about its innards? It is not likely anything except a transformer and transformers basically work either way. There are some ratio and loss effects as AZ Nomad noted so your actual voltage output will be a little less than what you might expect. If you supply the low voltage winding with 24 VAC you should be able to get about 0.14A from the high voltage winding at a high enough voltage to operate a nominal 110-120V device. Monitor the temperature to be sure it is not overloaded. The three prong grounded plug does not tell anything relevant about it. Don Young |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 18:36:57 -0600, Matt
wrote: AZ Nomad wrote: On Sat, 07 Feb 2009 18:49:25 -0500, Phisherman wrote: On Sat, 07 Feb 2009 17:23:32 -0600, Matt wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If you do as you say, you'll get 1.2 volts output. You need a step up transformer. He'd get 120vac because he'd connect the 24VAC to the 24VAC side. The problem is going to be loses and power considerations. He'll be lucky if he ends up with enough power to run a clock. Why wouldn't the efficiency and power rating be about the same in both directions? The efficiency might well be the same in both directions, but that efficiency is some number n that is less than 1. If it is the same in both directions, the efficieny of two in a row is n squared, and that will be even lesser than one. So if n is 7/8 (0.875), n**2 is 49/64 or about 0.75. The power available to the first transformer is for all practical purposes, unlimited, so the current in the primary winding is determined by its impedance and the 110 volts powering it. The current in the secondary is found by I = E/R, where R is the impedance of the secondary winding, and E is 24 volts. Now that you know what output I is, and rather than calculate it, the transformer probably says on it, that it's 300 ma, or 1500ma, the input current available to the second transformer isn't unlimited like the input to the first. It's maybe 1500 ma max. Raising the voltage from 24 to 110 will lower the available amperage by reciprocal factor. So if the voltage is 110/24, the max amperage is 24/110 * 1500 milliamps. That's about 0.22 * 1500 = 330 ma. And assuming the numbers I assumed, that will be your maximum. Less actually because the transformer is not 100% efficent. I don't know if you will get 110 volts or not. It would be interesting to do it and see what you get. Wouldn't be at all surprised if it is lower like the AZ said. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 18:34:52 -0600, Matt
wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. If it is an AC output and not a DC output wall wart then you can connect 12 volts to it and get out about 120 volts if it is normally a 12 volt output. Just put the 12 volts to the normal 12 volt output and the prongs will have 120 volts on them . You have to check to see how much current or how many watts the transformer is rated for as not to overload it. If your wall wart is good for 12 volts at one amp, then about all you can draw at 120 volts is 1/10 of an amp. Usuallly transformers do not care if they are connected up either way. Sometimes the output voltage will exceed the insulation of the wiring. Thanks. I am measuring about 25.7 VAC at the output when the input is 117.5 VAC. The thing is labeled "Plug-in class 2 transformer, Input: AC 120V 60Hz 35W, Output: AC 24VCT 700 mA". See below. So it is producing well over its nominal voltage. Can I conclude that it is unregulated---that it is just a plain old transformer? I think it tends to indicate that. Of course the voltae will drop when there is a load, because all the current has to go through the secondary winding which has internal resistance (called impedance for alternating current, but when it is only 60 cps, the impedance might not be much greater than the resistance your direct current ohmmeter measures.) When there is no current flow, that resistance has no effect, causes no voltage drop. Can I expect the same _power_ capabilities in normal and reverse direction? Your remark about current seems to indicate that. Yes and no. Look above at the power rating in the normal direction. 35 watts input, but only 24 volts * 700 ma output. The product is as someone said 16.8 watts, which is less than half of the input power. When you go the other direction, it will have the same power capability in that it will also put out slightly less than half of the input, or something like 8 watts. I'm really not sure, but would you say the answer to your question should be yes or no? Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. It has a 3-prong (grounded) plug. What could that tell somebody about its innards? |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sat, 07 Feb 2009 17:23:32 -0600, Matt
wrote: Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. Yes you can, but keep in mind they are only something like 80% efficient at best, and your maximum primary current will be the rated output of the device. This means a 1 amp wall wart will put out 100ma of current at 120 volts from a 12 volt supply. In an AC wall wart there is only a transformer. Don't try it with a DC output unit though!!!! |
Using an AC-to-AC wall wart transformer/adapter in reverse
On 2/7/2009 3:23 PM Matt spake thus:
Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. You might be interested in this guy's pages: http://www.dogstar.dantimax.dk/tubestuf/index.htm He builds vacuum tube circuits, and some of them are powered by 2 wall-warts back-to-back, just as you're asking about, like this power supply used for one of his projects: http://www.dogstar.dantimax.dk/tubestuf/sappower.htm This circuit supplies more than 400 volts of B+ for a small tube amplifier (using a voltage tripler), as well as several other voltages. So yes, it can be done. -- Personally, I like Vista, but I probably won't use it. I like it because it generates considerable business for me in consulting and upgrades. As long as there is hardware and software out there that doesn't work, I stay in business. Incidentally, my company motto is "If this stuff worked, you wouldn't need me". - lifted from sci.electronics.repair |
Using an AC-to-AC wall wart transformer/adapter in reverse
mm wrote:
On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sun, 08 Feb 2009 01:10:22 -0600, Matt
wrote: mm wrote: On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. Well, you can measure the resistance of the 120volt relay, and from that do a pretty good calculation of the current it will draw, and compare that with what I said would come out of the reversed transformer. I think I said 300 ma and 8 watts, but you can check. But that was when I guessed the first transformer was 1500 ma, and someone said it was half that. So that should give you a good idea of whether it would work, and then you can try it and see. It shouldn't take long to try it. And then if you have to you can get a 24vac relay. I think they are easily found. |
Using an AC-to-AC wall wart transformer/adapter in reverse
mm wrote:
On Sun, 08 Feb 2009 01:10:22 -0600, Matt wrote: mm wrote: On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. Well, you can measure the resistance of the 120volt relay, and from that do a pretty good calculation of the current it will draw, and compare that with what I said would come out of the reversed transformer. I think I said 300 ma and 8 watts, but you can check. But that was when I guessed the first transformer was 1500 ma, and someone said it was half that. So that should give you a good idea of whether it would work, and then you can try it and see. It shouldn't take long to try it. And then if you have to you can get a 24vac relay. I think they are easily found. Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sun, 08 Feb 2009 16:15:48 -0500, Bryce
wrote: mm wrote: On Sun, 08 Feb 2009 01:10:22 -0600, Matt wrote: mm wrote: On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. Well, you can measure the resistance of the 120volt relay, and from that do a pretty good calculation of the current it will draw, and compare that with what I said would come out of the reversed transformer. I think I said 300 ma and 8 watts, but you can check. But that was when I guessed the first transformer was 1500 ma, and someone said it was half that. So that should give you a good idea of whether it would work, and then you can try it and see. It shouldn't take long to try it. And then if you have to you can get a 24vac relay. I think they are easily found. Even radio shack should have something in stock, plus mouser.com and a couple other electronic supply websites. Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Even at only 60 Hertz? Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. |
Using an AC-to-AC wall wart transformer/adapter in reverse
Why wouldn't the efficiency and power rating be about the same in both directions? Exactly the same |
Using an AC-to-AC wall wart transformer/adapter in reverse
"mm" wrote in message Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Even at only 60 Hertz? Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. Probably not 10 times but more like 3 or 4 times more reactance than resistance for the relays. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On 2/8/2009 4:13 PM Ralph Mowery spake thus:
"mm" wrote in message Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Even at only 60 Hertz? Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. Probably not 10 times but more like 3 or 4 times more reactance than resistance for the relays. As pointed out, at a low frequency like 60 cps*, DC resistance = impedance to a good first approximation (in other words, close enough for gov't. work). * Cycles per second, the true measure of frequency. What's this "hertz" bull****? Since when did a car-rental company come into the picture? -- Personally, I like Vista, but I probably won't use it. I like it because it generates considerable business for me in consulting and upgrades. As long as there is hardware and software out there that doesn't work, I stay in business. Incidentally, my company motto is "If this stuff worked, you wouldn't need me". - lifted from sci.electronics.repair |
Using an AC-to-AC wall wart transformer/adapter in reverse
"David Nebenzahl" wrote in message .com... On 2/8/2009 4:13 PM Ralph Mowery spake thus: "mm" wrote in message Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Even at only 60 Hertz? Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. Probably not 10 times but more like 3 or 4 times more reactance than resistance for the relays. As pointed out, at a low frequency like 60 cps*, DC resistance = impedance to a good first approximation (in other words, close enough for gov't. work). When the reactance is 3 or more times the DC resistance that is nowhere near enough for gov't work. The coil will smoke if you use the DC resistance even at 60 cps. if the power supply will put out the current. Oops , forgot about the big bailout going on now by the government and the big crash that is going on now. That banking and loan calculations were good enough for gov't. work. It smoked too. |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sun, 08 Feb 2009 01:10:22 -0600, Matt
wrote: mm wrote: On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. Get one. They are very common, plentiful, and cheap. If you were in Kitchener Waterloo I'd GIVE you one. |
Using an AC-to-AC wall wart transformer/adapter in reverse
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Using an AC-to-AC wall wart transformer/adapter in reverse
On 2/8/2009 4:44 PM Ralph Mowery spake thus:
"David Nebenzahl" wrote in message .com... On 2/8/2009 4:13 PM Ralph Mowery spake thus: "mm" wrote in message Coil current with AC applied will be much lower than the value calculated from DC resistance ... by perhaps a factor of ten or more. Even at only 60 Hertz? Inductive reactance is the dominant contributor to impedance here and it is proportional to frequency and isn't there at DC. I agree with mm's comment about 24vac relays. Your HVAC thermostat may have a solid-state relay driver that won't be happy with the unexpected load. Probably not 10 times but more like 3 or 4 times more reactance than resistance for the relays. As pointed out, at a low frequency like 60 cps*, DC resistance = impedance to a good first approximation (in other words, close enough for gov't. work). When the reactance is 3 or more times the DC resistance that is nowhere near enough for gov't work. The coil will smoke if you use the DC resistance even at 60 cps. if the power supply will put out the current. Nonsense. Don't believe me? Get ahold of an 8 ohm speaker and measure the resistance (DC resistance) using a DMM. It'll be within 10% of 8 ohms, which is the rated *impedance*. And this covers the audio spectrum (up to 20 kHz). Oops , forgot about the big bailout going on now by the government and the big crash that is going on now. That banking and loan calculations were good enough for gov't. work. It's a figure of speech, my man. -- Personally, I like Vista, but I probably won't use it. I like it because it generates considerable business for me in consulting and upgrades. As long as there is hardware and software out there that doesn't work, I stay in business. Incidentally, my company motto is "If this stuff worked, you wouldn't need me". - lifted from sci.electronics.repair |
Using an AC-to-AC wall wart transformer/adapter in reverse
On Sun, 08 Feb 2009 19:18:20 -0600, Matt
wrote: wrote: On Sun, 08 Feb 2009 01:10:22 -0600, Matt wrote: mm wrote: On Sat, 07 Feb 2009 18:34:52 -0600, Matt wrote: Ralph Mowery wrote: "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Why do you want to do this, btw. Is there no 110 outlet at that location? Maybe you can run one. Trying to switch a relay that has a 120VAC coil using a nominal 24VAC signal from a digital HVAC thermostat. I don't have a relay with a 24VAC coil handy. Get one. They are very common, plentiful, and cheap. If you were in Kitchener Waterloo I'd GIVE you one. Shucks, I wish I were there ... but would it handle say 20A @ 120VAC? To run a heater. I just paid $20 for a 30A relay, waiting for it to get here ... No, it is rated at 15 amps, I think. |
Using an AC-to-AC wall wart transformer/adapter in reverse
Yes, and AC output wall wart should provide the needed
voltages. However, we don't know if the application would work just fine. How many watts of 24 VAC do you have, and how many watts of 110 VAC do you need? Should be able to convert 24 VC to 110 VAC. You won't have much amperage to use, on the 110 VAC side. -- Christopher A. Young Learn more about Jesus www.lds.org .. "Matt" wrote in message ... Suppose I have a plug-in transformer that reduces 120VAC power to some lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the reverse---increase a low-voltage source back up to 120VAC. Would there be a problem in connecting the low-voltage power to the plug-in prongs of the wall wart (instead of the normal use: plugging the prongs into the wall outlet) and expecting to get high-voltage power back out the other end? I guess my question is answered if I know that there are no components other than the transformer inside the wall wart. My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or 24VAC) to convert 24VAC back up to 120VAC. |
Using an AC-to-AC wall wart transformer/adapter in reverse
I think you'll find that on most 110 VAC wall warts, the
110 VAC side is insulated for 110 VAC. -- Christopher A. Young Learn more about Jesus www.lds.org .. wrote in message ... You know of course that it can only handle very small current levels and that it would need the original output circuits would will be handling 120V when they are only insulated for 12Volt In short, it is a bad ideal Get the right tool for the job. Joseph E Meehan |
Using an AC-to-AC wall wart transformer/adapter in reverse
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