Transformer temperature

[michael howarth 1Participant @michaelhowarth1]

[michael howarth 1Participant @michaelhowarth1]

The small transformer (240v-12v) which powers my pond pump is reaching quite high temperatures. At an ambient temperature of 19 deg C yesterday morning the temperature of the transformer was 48degC as measured with an infra red thermometer. In the heat of a couple of days ago it was barely touchable suggesting probably about 60 deg C. I know that transformers get warm but this seems to be a bit excessive. Advice will be appreciated.

Mick

[MuzzerParticipant @muzzer]

Don't overthink it. The insulation system inside that transformer will be rated at something like 130C, 155C or even 180C. They are tested extensively and will almost certainly incorporate a thermal fuse if indeed there is an actual overtemperature situation.

If you look carefully at the documentation, you may find details of the temperature rating – or at least where you could find out about it. For interest.

To lower the temperature, if you felt that was desirable or commercially justifiable, you'd need to make everything bigger (more copper and larger surface area). You'd then struggle to sell it at a sensible margin against the smaller competition.

We like to chortle about "elf and safety" and "red tape" but in a more grown up world, the regulations are designed to ensure that products are safe to use, including fire hazard, electric shock hazard and touch temperature.

Murray

[Gordon TarlingParticipant @gordontarling37126]

It is also entirely possible that your pump is drawing more current than it used to. This could be for many reasons, including moisture ingress. Protection for a stalled motor should be built in, though this won't necessarily work for a motor that is starting to tighten up for some reason.

[MuzzerParticipant @muzzer]

Protection of the transformer is to ensure there isn't a fire or touch hazard and also to ensure that the electrical insulators are not compromised by the temperature, so it will "necessarily work". This safety stuff is not some hobby activity but actually the result of decades or more of learnings from death, injury and industrial accidents.

Murray

[JasonBModerator @jasonb]

Any restrictions in the pipework like a build up of blanket weed on the pump strainer, dirty filter, you also get a lot of insect growth inside the pipes and even around the impellor this time of year. All will make the pump work harder and draw more current

[michael howarth 1Participant @michaelhowarth1]

I can give a little more background. The pump system is less than a year old. The first transformer failed after about 6 months and this too seemed to reach excessive temperature. It was replaced free of charge but the replacement is still reaching the temperatures outlined above. The transformer is an IP68 . The pump is 12V 10watts and the UV lamp 5 watts.

I have just Googled IP68 and it appears to have a working temperature of 0-25 deg C

Mick

[MuzzerParticipant @muzzer]

IP68 (ingress protection) is a test to check for ingress of dust and water. It has nothing to do with temperature.

I wonder how you have determined that it has reached "excessive temperature"? On what basis do you make this judgement?

[michael howarth 1Participant @michaelhowarth1]

Muzzer…….I got the specification IP68 from the user manual technical specifications….obviously not much use. My feelings about the excessive temperature (48 degC) are I suppose quite subjective but this is only a small transformer, say 50 x 50 x75 mm and the pump/uv demand is only 15 watts. I would be perfectly happy to be assured that there is no problem but the warranty runs out next month.

Mick

[John RuddParticipant @johnrudd16576]

Mick,

Did you purchase both pump and transformer as a package? If yes, then I'd take it up with the supplier on the basis that the first transformer had failed and the second replacement is getting hot. Suggest there may be a problem with the pump and ask how they will resolve this?

[I.M. OUTAHEREParticipant @i-m-outahere]

You may be forcing the pump to push too much head or lift so it is under full load all the time , restricting the outlet pipewirk diameter will do the same .

Disconnect the outlet on the pump then let it run and see if the temps on the transformer drop .

The uv lamp may be shorted causing more current draw than usual ?

If all else fails upgrade he power supply to somehing that can put out more power .

Have a look at your transformer it should have a rating of at least 1.5 amps preferably 2 amps or more .

V X A = W (12×1.25 =15 w ) you state your pump is 10w and the light 5 w = 15w but one really never knows exactly how much power a pump will pull under full load ( unless you tested it ) a factor of X1.5 of the expected maximum is what i use as a minimum.

I'm sure there will be an electronics / electrical engineer who will come along shortly that will want to correct me for things like RMS or delve into power factors and electrical losses in cables etc etc etc .

Ian

[not done it yetParticipant @notdoneityet]

I would be checking output voltage and current to find the wattage of the load as a first step. I might then be looking at input power v. output power to check for efficiency, if not overloaded. It cannot be good if the case temperature is near 50C (in the shade) as the internal wiring temp may be considerably higher.

A decent one should only be losing about 3-4W as heat. Do check your IR thermometer as some are notoriously inaccurate, but the power supply should not get to untouchable temperatures from internal heat generation, that is for certain!

I would not think that an impellor pump (non postive displacement) would be affected by blockage in pipework, only if the impellor is rubbing. Is it direct drive or magnetically coupled? If the latter, is it driving continuously or is the motor decoupling continually?

[michael howarth 1Participant @michaelhowarth1]

Quite a few things to investigate there. Firstly I think I shall do an easy bit and de-restrict the pump out flow …..less pretty but more flow.

Back soon.

Mick

[I.M. OUTAHEREParticipant @i-m-outahere]

Posted by not done it yet on 23/06/2017 12:49:05:

I would be checking output voltage and current to find the wattage of the load as a first step. I might then be looking at input power v. output power to check for efficiency, if not overloaded. It cannot be good if the case temperature is near 50C (in the shade) as the internal wiring temp may be considerably higher.

* Efficiency is irrelevant as the output power vs pump requirement is all that matters.

A decent one should only be losing about 3-4W as heat. Do check your IR thermometer as some are notoriously inaccurate, but the power supply should not get to untouchable temperatures from internal heat generation, that is for certain!

* Agreed.

I would not think that an impellor pump (non postive displacement) would be affected by blockage in pipework, only if the impellor is rubbing. Is it direct drive or magnetically coupled? If the latter, is it driving continuously or is the motor decoupling continually?

The load on an impellor pump increases until cavitation occurs , if power is so low that cavitation cannot occur the vortex inside the pump can collapse causing flooding of the impeller and it will stall or load up or become a propellor instead of an impellor and this gives the same sort of current draw a pump would have on start up but it is continuos .

Ian

Edited By XD 351 on 23/06/2017 14:31:28

[michael howarth 1Participant @michaelhowarth1]

I have now de-restricted the flow from the pump and after a few hours the temperature of the transformer remains much the same, if not a little higher at 49degC. Ambient temperature 22degC. The unit has a maximum pumping head of 1.25 metres but is only about 30cm below the surface.

I will attempt to measure the current output (12v AC) from the transformer tomorrow. Would I be correct in saying that I can do this by connecting a multimeter in series with one of the two output leads? The transformer output is listed as 1670mA.

Mick

[SamsarandaParticipant @samsaranda]

I have "messed about" with ponds of all sizes for at least forty years and my past experiences tell me that Mick's problem with the transformer will be the load experienced by the pump. At this time of year all ponds will be loaded with small pieces of vegetable matter free floating in the water, when this vegetable matter passes through the pump it will gradually clog the impeller and therefore increase the consumption from the transformer and hence cause the temperature to rise. As well as the vegetable matter accumulating in the pump housing, at this time of year there will be minute water snails that have hatched and probably lodged in the impeller housing, the only way to guarantee reducing the loading on the pump is to regularly dismantle the impeller housing and clean it out, unfortunately at this time of year with a small pump which it appears Mick's is, this may need to be done daily to keep the pump free flowing, and the temperature at an acceptable level. There are pumps that will give better performance with accumulated solids but without knowing which pump we are discussing difficult to comment further.

Dave

[SillyOldDufferModerator @sillyoldduffer]

Posted by mick H on 23/06/2017 17:01:36:

…

I will attempt to measure the current output (12v AC) from the transformer tomorrow. Would I be correct in saying that I can do this by connecting a multimeter in series with one of the two output leads? The transformer output is listed as 1670mA.

Mick

Yes, provided your multimeter has a suitable AC current scale. Quite a few are DC current only. If it does measure AC current it's likely to have a single 0-10A range only, but that's OK for what you're doing.

Another way of checking if you can manage a bit of ad-hoc wiring, is to load the transformer with car indicator bulbs (a 10W and a 5W in parallel). That will replicate the transformer's 15W design load: if it overheats the transformer is faulty (shorted turns?) or inadequate. If the transformer stays cool, the problem is in the cable, or more likely, the pump &/or lamp.

Dave

Edited By SillyOldDuffer on 23/06/2017 18:05:36

[Phil WhitleyParticipant @philwhitley94135]

Can you post up some pics of transformer and pump? the chances are that this is chinese made and as you have already had one failure, the chances are you are well on the way to the next. The best way to slow the flow on a pond pump is to bleed off water from the pressure side back into the pond via a T peice and a valve, so you can slow the flow without choking the pump on the pressure side. 1.67A is not a lot and you could get a, say, 3 amp transformer, and see how that performed, it will make no difference to pump performance, but will run much cooler. Chinese mains dropper transformers do run stinking hot, and do pack up, as you have found out. My water feature has a mains submersible pump which has given no problems for several years now, and I don't think it was new when it went in. As I have mentioned before, there is zero product testing going on today, all "CE" marked good are supposed to conform with standards laid down by the EU, but it is up to the manufacturer to do their own testing, and to provide "proof of compliance" paperwork. It is very common for, shall we say, foreign made equipment to fail to reach its rated output and far exceed its claimed current demand by a sometimes very large margin!! Muzzers faith in the system is charming, but a little misplaced

[David JuppParticipant @davidjupp51506]

Posted by Phil Whitley on 23/06/2017 19:24:59:

The best way to slow the flow on a pond pump is to bleed off water from the pressure side back into the pond via a T peice and a valve, so you can slow the flow without choking the pump on the pressure side.

That is actually likely to increase the flow through the pump (though reduce it through the visible water feature) and therefore may even increase the absorbed power. Restricting the outlet of a centrifugal pump will reduce the power consumption. Large centrifugal pumps are commonly started against an almost closed delivery valve to limit current surge (less so now that VFDs are commonplace).

[David George 1Participant @davidgeorge1]

Hi Mick

I have a small Hoselock pond pump on a small water feature and the power supply has always run hot. When it was new I rang support and was told they do run hot but if it fails or causes any problem call back and they would replace it. That was four or five years ago. Its a 240 to 24v 1 amp model 62531-000. its very hot to the touch and always has been I think it helps to keep my tools rust free in winter.

David

[Tim StevensParticipant @timstevens64731]

Remember, if you are using filament lamps as a load to check your system, that the bulb will only have the stated characteristics (eg 12v 6W, and therefore a working resistance of 24 ohms*) when it is getting the full 12 volts. Put it in series with something else and the voltage at the bulb will be lower, the filament will not get so hot, and its resistance will drop. A cold filament will draw several times the current of a properly hot one. This would be clear to us all if only cars still had ammeters.

One factor which has not been mentioned is the ventilation of the transformer. A small amount of heat that can't get out will produce a large rise in temperature, after a time.

Cheers, Tim

*PS if memory serves …

Edited By Tim Stevens on 23/06/2017 21:32:06

[michael howarth 1Participant @michaelhowarth1]

Thank you for your interest and comments gents. The outfit that I have is a " Blagdon 3000 Inpond 5 in 1". So quite a reputable make but I would guess having origins in China. The outfit performs well and does what it says it will do, keeping the pond crystal clear and apparently well oxygenated. It is about 10 months old and the transformer has always run very warm from day 1. As previously mentioned, the original transformer failed after about 7 months. I will be giving it a routine clean out over the weekend and will obviously check for obstructions etc.

I had a look at the charger unit for my Bosch drill and the power output is much the same as the pond transformer 14.4V at 1.5 amps and this unit is barely warm if left on all night. Strange. Something just does not feel right although as one can deduce, my knowledge of these things is scant and I may be comparing apples with pears. I have a feeling that I will probably end up with a transformer with a greater output but I find this problem intriguing.

I emailed the manufacturer this morning but their replies are within 7 days.

Mick

[John OlsenParticipant @johnolsen79199]

Quite likely the transformer is a bit mean on copper and iron and so is not up to the job. After all, it only has to last until the guarantee runs out. One thing to try is to measure the magnetising current, eg the input current from the mains with no load on the output. This should be quite low, less than 10 % of the current for full load.

Many years ago where I was working we were having trouble with the mains transformers in a PYE VHF receiver. The transformer was rated at 23 VA. With no load on the secondary, they were typically taking 18 VA just for magnetising current. So they ran quite hot just on no load. An interesting check was to gradually reduce the mains input voltage with a Variac transformer. A 10 % reduction in input voltage dropped the magnetising current right back to about what is should have been, eg a couple of VA or so. So we had a transformer rewound with about 10 % more turns, which worked perfectly. Of course, we were not allowed to do this to the rest of the sets, since that was an unauthorised mod, so we had to put up with just changing them all the time.

Actually, if you don't happen to have suitable gear to measure the input current, just running it no load and seeing how warm it gets would be worthwhile.

John

[not done it yetParticipant @notdoneityet]

John is quite right about modern day transformers, particularly from china. I believe all new units are required to have a rating shown. This ranges from one to five, or six, in roman numerals, the best being the higher numbers which waste far less power than the poor ones.

Basically the magnetic flux is lost from the unit, instead of being concentrated and used where it is effective or the windings are substandard in the poor units.

Think about things a little and you will realise the turns ratio, to reduce the voltage from 240 to 12V is 20:1. This can theoretically be achieved with 20 turns on the primary and just 1 on the secondary. Or it might be achieved wit 200 and 10,

2000 and 100 or any other combination of that ratio. The lower numbers will not work as well as higher numbers.

Also, the transformer core needs to be designed so as not to retain its magnetism (it needs to change at the mains frequency) and the induced currents (eddy currents) in the core material need to be minimised (that is why cores are laminated and electrically isolated between laminations).

Further design parameters, like isolating the primary (at mains voltage) from the safe secondary voltage, to avoid mains voltage being fed to the output in the case of failed windings, can be arranged with windings separated to each end of the core or one winding enclosing the other. Both work, but the efficiency is not the same!

Good transformer design is not a simple matter as all the above aspects are inter-related!

[Russell EberhardtParticipant @russelleberhardt48058]

Transformers are designed to run hot. Modern winding insulation materials can withstand quite high temperatures. A 27 C temperature rise is by no means excessive. When we used to get transformers made we would specify a 125 C thermal fuse to be embedded in the windings.

Are you measuring the temperature of the windings, the laminations, or a plastic case? You can measure the winding temperature by measuring the primary resistance when cold ( at a known temperature) and then again after giving it a long run at full load. It is then a simple matter to calculate the temperature from the known temperature coefficient of the resistance of copper.

Even the lowest spec wire insulation is rated for 100 C continuous and the more usual class F is rated for 140 C.  Maximum surface temperature of an enclosure that can be touched is, if I remember right, 65 C.

Russell.

Edited By Russell Eberhardt on 24/06/2017 09:31:13

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