anyone noticed that heater have internal thermostat that switches them off, while the

[KevinK]

I have 3 – 300W heaters, one about 1 year old, one about 8 months and one about 2 months, all connected to one and the same controller and because of that all have their heater set at max, as the controller handles the temp the 3 heaters are all different brands.

watching the heaters, and a external amp. meter the heater go on and off all the time while in heating mode, not all at once but as followed, as i had timed it (2 heaters)

heater a:

2:16:40 off
2:17:45 on
2:20:25 off
2:21:.35 on
2:23:53 off
2:25:55 on

that is 192 seconds off from the 555 sec. / close to 35% off

heater B different times within the same 2:16:44 to 2:25:55 as heater A

26 sec. off
15 sec. off
28 sec. off
28 sec. off
26 sec. off
27 sec. off
27 sec. off

that is 177 sec. off from the 555 sec, / close to 32% off

so independently from another thy go off and on (and my third heater as well)

would thy have a internal thermostat that allows them to get only a X temp in the glass tube before thy go off

the main breaker popped from our heat pump in the house, and thus it became colder in the house overnight, and found that the heaters did not keep up, hmmmm. 32 to 35% of the time thy are off

[hfp75]

Do a test and in the controller lower & raise your on/off temps.... Then watch your on times...... If one is not on as much maybe the thermostat inside isn't letting it turn on...

I had a prob where my one heaters temp was set to low and even though the controller had turned it on, it was turning itself off... Internal thermostat issue. My prob was solved by turning up the temp more....

You might have a dead heater...

[Borderjumper]

It's one of the mysteries of life kevin! :mrgreen:

[KevinK]

Do a test and in the controller lower & raise your on/off temps.... Then watch your on times...... If one is not on as much maybe the thermostat inside isn't letting it turn on...

I had a prob where my one heaters temp was set to low and even though the controller had turned it on, it was turning itself off... Internal thermostat issue. My prob was solved by turning up the temp more....

You might have a dead heater...

it is not the timer/controller that is going off, because that would mean all off or all on.

the 3 heater are on one channel, that is calling for on, and with one of those 3 way split it is going to the heaters that are all turned to max, as the controller handles the temp control. interestingly is that heater a each time is off for about

could be as you mention be a slightly faulty heater (but all 3), thy do heat, only as the timing suggest on and off for heater A is each time around 65 sec. off and for heater B each time in the 27 sec range

[duncangweller]

I wouldn't set them at max just in case the apex fails/doesn't switch one off or something goes sideways and then you will have a heater going until the tanks boiling! Better two fail safes than just one.

[Simons]

yeah I agree, one of the most common tank crashes results from a 'stuck' on heater.

I stay away from the internal switches, and use titanium heaters, when they are powered they are on and I have two temp probes to verify shut off temperatures.

Even if your Apex fails, the socket will fail with it's "SET" condition, so if they are SET OFF and fallback is OFF an Apex failure shouldn't ever allow them to be 'on' by error.

[KrazyKuch]

I have a theory. I have never looked at the internals to a heater before. But it would make sense to me to pulse the heat on and off. For the thermistat to work properly you would want the heating element turned off so that you can get a better water temperature. Remember that it will be hotter inside the heater then out.

this is just a theory and not fact...now i feel the need to test this theory with my heaters!

[KevinK]

this could be the one,

if you think about it, how can it (when not controlled by a external device) read accurate temperatures if it is surrounded by warmer water around the tube, or a warmer internal temp in the tube.

this would mean that it will go off each ... sec for a little while to get a reading, and if not at the desired temp, it kicks on again

[mike31154]

Are all the heaters the same size/wattage? You mention they are different brands. Most are built pretty much the same with a simple bimetallic strip that switches them on/off. Dissimilar metals fused together bend at a different rate in relation to temperature. A set of contacts at the end make or break in response to the bending, completing or opening the circuit to the heating element.

Many things come in to play that influence the behaviour of the the bimetallic switch. Heater location (in relation to flow), size (both physical & wattage), variations/quality in manufacturing, water level in relation to the bimetallic strip, age of the heater, etc. Over time, the contacts become pitted & fail due to arcing every time they open/close. Pitting will increase contact resistance & alter the cycling rate of the heater, worst case they fuse together & the heater stays on as described by many folks who've had them fail that way.

Not sure having all three connected to a single channel on your controller is a good idea either. You've taken the redundancy of having 3 heaters & connected them to a single point of potential failure. Also make sure that the single channel you have them on is rated to handle the wattage of the 3 heaters. I assume it can, since it appears you've been running that way for a while, but never hurts to double check, since as mentioned, as contacts wear resistance increases and with it the actual power draw of each heater.