How to bypass an auto shut off?

[Regent]

I have an electric blanket that as an auto shut off after an hour! I want to use the blanket to warm up my flower seedling and I need it to always be on.
Can anyone tell me if the auto shut off is on the circuit board or in the blanket itself? And can I bypass this annoying problem?

[Regent]

Re: How to bypass an auto shut off?

I did some research & I found that on the circuit board (as shown in the photo) there is a 3 pin ZTT 4.00MG ceramic resonator (blue) & they sometime can be use as a timer. Can someone confirm if this is where the one hour auto shut off is?
By the way, the reason why this company (coz-e) as an auto shut off after an hour is in case you fall asleep. It as nothing to do with temperature control.

[goontron]

Re: How to bypass an auto shut off?

I don't see why or how a resonator could be used in a temp control circuit.
it is safe to assume that will either stop the auto shutdown or stop the unit from coming on at all.

[Longbow]

Re: How to bypass an auto shut off?

If the blanket is controlled by a uPC, the 4 MHz resonator is the main clock. Many processors will also use a secondary 32KHz clock crystal to time the serial bus and for real time displays, etc. I doubt if a blanket is that complex. Slowing one or both of the crystals might delay the shut-off depending upon the circuit, but the auto shut off itself will still happen because it is programmed into the software.

Even though it is tempting to use an electric blanket, it is a bad choice for use around water (plants) and you have very little control over the heat. Have a look a silicone heating strips. This solution is ideal for use around water and the control requirements are modest.

http://www.watlow.com/products/heate...ne-heaters.cfm

[Regent]

Re: How to bypass an auto shut off?

"the auto shut off itself will still happen because it is programmed into the software."

Thank You very much Longbow for your excellent explanation!!!! I will be looking for another option like a silicone heating strips!

[budm]

Re: How to bypass an auto shut off?

There should be a device called TRIAC on the board which is used as a switch to supply power to the heater, it is turn on by the micro controller, so if you want to have the heater on all the time, then you have to bypass the TRIAC,
On the left side you can see HI (HOT IN), NI (NEUTRAL IN), and SI (SWITCH IN), the Neutral IN is fed to a fuse F1 which is connected to N where one wire of the heater is connected to, the other wire of the heater is connected to L which is the output side of the TRIAC.

[Regent]

Re: How to bypass an auto shut off?

Thanks budm for your reply. I assume your talking about Triac Z0405MF? There are two of them. I attach two pics, one from the back of the ic board & the other one the front.
Could please you explain which one needs to be bypass & how I should do it?
Circuit boards are not my specialty! Sorry about that! But I do want to learn.

[budm]

Re: How to bypass an auto shut off?

This controller looks like my Sunbeam thrown blanket, now I see the ON/OFF switch on the LED side of the board, that means the SI is not the switch but the sensor to detect how hot the blanket gets, if you bypass the circuit, the heater may just keep on heating and can over heat, I think that is one of the safety it has, so I do not feel safe for you to bypass the circuit, you can have big fire instead.

[Regent]

Re: How to bypass an auto shut off?

Thanks for your help & advice budm!

[Regent]

Re: How to bypass an auto shut off?

If I keep the ON/OFF switch ON by holding it there with an elastic it will default to the low setting after the one hour auto shut off kicks in!
There are three settings low, medium & high. Every time you press the ON/OFF switch it bring you to the higher setting but if you hold the button while on the high setting it will default to the low setting after an hour.
My question is how can I bypass the low & medium and go directly to the high setting from the IC board?

[sam_sam_sam]

Re: How to bypass an auto shut off?

Here is what I would do use all parts there are except the controller board and built my own controller using what mirco controller you can program

[budm]

Re: How to bypass an auto shut off?

Jump HI to L (do it at your own risk), then you will have full power to the heater, the only way to tun off is to unplug it, otherwise you'll need to re program the controller to do what you want to do.
You can also make a box with switch that will put a diode in series with the heater (50% power) or can be bypass with a switch to give full power. You need to know the current draw of the heater to get the correct size Diode.
If the heater is less than 300W, then you can use this:

http://www.westsidewholesale.com/lut...300nlh-wh.html

[Regent]

Re: How to bypass an auto shut off?

Thanks for your help.

[budm]

Re: How to bypass an auto shut off?

That dimmer controller may work. Let us know what you end up with.

[Regent]

Re: How to bypass an auto shut off?

I also believe that a bypass from HI to L and the Dimmer Switch might very well work! The specs on the blanket says 60 watts. Again thanks for your help.

[budm]

Re: How to bypass an auto shut off?

Only 60W, must be smaller blanket than mine, at HI it uses about 160W on my blanket. That dimmer should work just fine and will allow you to adjust the power as well to suit your need.