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drewp
Plug-in transformer numbers?

Hi folks, I'm changing out the plug-in transformer on my mothers home security system. The present plug-in reads: Class 2, Input: 120VAC 60HZ 0.30A Output: 16.5VAC 25VA. I just picked up a new one at a very reputable electronics supply store in my neighborhood (it's where all the contractor shop). It reads: 120VAC 60HZ 0.43 A 16.5VAC 45VA. They counter guy assured me there won't be any problem. Before I install it, I'd just like to hear from someone else that this plug-in will be fine. I don't want to slowly fry out my mothers system. I can get the same input/output one but I'd have to order it on-line. Thanks for your input.

JLMCDANIEL
Re: Plug-in transformer numbers?

There should be no problem using the new plug in, you have the same input/output voltages and just the ability to carry a slightly larger load. The alarm system will maintain the same load it always has had.

Jack

drewp
Re: Plug-in transformer numbers?

Thanks very much for the quick reply Jack. I wanted to install it today...but was going to wait until I heard from another that there shouldn't be any issue.

function
Re: Plug-in transformer numbers?

I have changed out a couple of transformers recently. If the output amperage is higher, that will just charge the battery faster, if any change at all. Output voltage needs to be the same, obviously, and output amperage should not be lower.

Of course you may run across a transformer with output amperage that is lower than listed on the label, that really irks the Mrs when it is a backup transformer for her breast pump.

keith3267
Re: Plug-in transformer numbers?

Here's another vote for no problem. The alarm system will only draw what it needs. The VA rating is the capacity of the transformer, kinda like horse power in a cars engine. The old transformer only had a 25VA capacity where the new one has a 45VA capacity. Much like replacing your old 4 cylinder Camry with a new Camry with a V6.

The new transformer will run a little cooler and it is a little more efficient, 87% vs 82% for the old one.

drewp
Re: Plug-in transformer numbers?

Thanks for the advice everyone. I'm actually changing out her transformer because I heard it buzzing a bit more loudly than normal, I noticed the housing was becoming a bit discolored AND it was pretty hot to the touch (I know they'll usually get a bit warm). Why would the original installer (or anyone for that matter) use the 25VA capacity if the 45VA is available AND more efficient and cooler? I suppose there comes a point when the increased "capacity" becomes either inefficient or unusable?

keith3267
Re: Plug-in transformer numbers?

Reviewing your last post here is causing me another concern here. There may actually be something else in the system that needs attention. Some other posters have referenced a battery, but you have not. If the system has a rechargeable battery in it to provide security during a power out, then the issue could actually be with the battery and not the transformer.

As batteries age, the start to have greater internal parasitic losses. This results in shorter discharge time and higher current to recharge and maintain a charge. That would cause a greater load on the transformer.

The battery may not be bad to the point that it needs to be changed just yet, but to answer your last question, the original transformer may have been sized for a new battery and not have been sized to account for an aged battery. Sometimes engineers don't look down the road very far.

Because the transformer has been running hot for awhile, I would go ahead and replace it, but if there is a rechargeable battery, I would look at changing it as well. The excess heat generated in the transformer trying to keep an aged battery charged up does shorten its lifespan. An aged battery is only going to get worse and it could cause even the newer transformer to overheat as well.

drewp
Re: Plug-in transformer numbers?

Thanks for the heads-up. The battery is relatively new. The previous battery was in for a "number" (I can't even tell you how many) of years and this may have begun to wear out the previous transformer

Mastercarpentry
Re: Plug-in transformer numbers?

You'll be OK here so long as the rest of the system is OK. Charge regulation won't be an issue as this is happening inside the controller. I know that because the transformer is AC output, which has to be changed to DC to charge a battery.

I never throw away any old wall-warts (transformers) which work and are marked. I use them for repairs and other projects. As long as you:A- make sure the output type is matched* (AC to AC or DC to DC); B- match the output voltage; C- match the polarity at output; and D- make sure the new one has the same or higher output current rating then they will swap. Using too big a transformer only reduces it's efficiency, the circuit downstream will draw only what is needed from it and no more so it's not going to burn anything up being over-capacity. *DC outputs can be either half-wave or full wave rectified and sometimes this matters, though half-wave rectification is a rarity these days.

Don't guess at these ratings and don't use unmarked transformers because they will show a higher output voltage on your meter than they do under load, and none of them will read what the label says exactly unless they have a regulator circuit built-in even with a load. And yes, generally manufacturers size these to be just adequate with little or no reserve capacity. You can tell how well they did by feeling it under load- at most it might be somewhat warm. Anything more than this means it's working too hard. In simpler circuits you can often go a bit above voltage- say a few volts, not five- because most simple circuits are not voltage-critical and are usually internally regulated if they are. That regulation has limits so stay within a few volts, and only above- never below the original.

I can't say how many 'dead' electronics I've fixed for free this way, but it's got to be reaching the multiple-thousand dollar range by now. A few minutes with solder and heat-shrink and Voila!- good as new.

Phil

Re: Plug-in transformer numbers?
Mastercarpentry wrote:

You'll be OK here so long as the rest of the system is OK. Charge regulation won't be an issue as this is happening inside the controller. I know that because the transformer is AC output, which has to be changed to DC to charge a battery.

I never throw away any old wall-warts (transformers) which work and are marked. I use them for repairs and other projects. As long as you:A- make sure the output type is matched* (AC to AC or DC to DC); B- match the output voltage; C- match the polarity at output; and D- make sure the new one has the same or higher output current rating then they will swap. Using too big a transformer only reduces it's efficiency, the circuit downstream will draw only what is needed from it and no more so it's not going to burn anything up being over-capacity. *DC outputs can be either half-wave or full wave rectified and sometimes this matters, though half-wave rectification is a rarity these days.

Don't guess at these ratings and don't use unmarked transformers because they will show a higher output voltage on your meter than they do under load, and none of them will read what the label says exactly unless they have a regulator circuit built-in even with a load. And yes, generally manufacturers size these to be just adequate with little or no reserve capacity. You can tell how well they did by feeling it under load- at most it might be somewhat warm. Anything more than this means it's working too hard. In simpler circuits you can often go a bit above voltage- say a few volts, not five- because most simple circuits are not voltage-critical and are usually internally regulated if they are. That regulation has limits so stay within a few volts, and only above- never below the original.

I can't say how many 'dead' electronics I've fixed for free this way, but it's got to be reaching the multiple-thousand dollar range by now. A few minutes with solder and heat-shrink and Voila!- good as new.

Phil

Good info Phil

keith3267
Re: Plug-in transformer numbers?

I agree it is good information too, except for one line "Using too big a transformer only reduces it's efficiency, ". That is not a given, there are too many factors when determining a transformers efficiency so that may or may not be true. Because the OEM transformers are usually "minimally sized" for the job, their load losses are pretty high. Load losses are exponential so going up in capacity by 25% can reduce load losses by as much as half, but usually at an increase of 25% in no load losses. No load losses usually account for about 20% of the total losses.

Total efficiency has to take in the no load losses which are 24/7 losses and the load losses, which although are higher are also dependent on duty cycle. If the transformer is under load 24/7, then the load losses are more important than a transformer that is under load for say only a few hours a day. In this case, I'd guess that the transformer is under load whenever the alarm system is on so it probably is closer to 24/7.

Materials, design and construction also play a big part in the efficiency. Better core material decreases no load losses and winding material (copper vs aluminum) wire size and design affect the load losses.

An indication of the transformers efficiency is the amount of heat that it gives off. That is total heat, not just the surface temperature of the transformer. All the electrical losses are in the form of heat.

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