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  1. #11
    Administrator bolsoncerrado's Avatar
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    Nov 2014
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    Yeah and mine is that perhaps his room temperature was too low and hence higher to reach 60C on his printer hmmm

  2. #12
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    Nov 2016
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    A heated bed is all about putting juice to the circuit. If the circuit has high impedance, they heat rise will be slower; conversely, if the impedance is low, they heat rise is very quick. Each heater system is designed for a specific impedance. This is -not- a rocket science concept if you look at it more simply, or basically.

    Your heated bed is a light bulb. It is radiating light, infrared light, but light none the less. And as in light bulbs, they are specifically designed to put out so much light given a specific voltage and -allowed- to draw current. A 60 watt light bulb is rated such because when you short out the wall socket with a light bulb, it uses 1/2 amp's worth of current to reach the 60 watts if you supply 120V. Watts is volts times current. Simple math that can be swapped around to meet any calculation.
    The amount of juice if nothing else. It can be potent juice or bland blend. Mornin' Joe if you will.

    What stops the Joe from flowing? Higher impedance as described in the first paragraph. Every wire connection is in itself an impedance. You loose a bit of Joe through the cracks, I mean the interface in the connectors. The wires themselves are acting like heaters, but you don't (or shouldn't) notice that. What normally happens in situations like this is that there is a huge impedance at one location in the heater pad circuit. Not the sensor, but the big cables. And there are many ways to find the culprit.

    But, coffee analogies won't cut it. Usual suspects are easier to locate and diagnose. Tools help tremendously! The nose is the first tool in burnt electronics. If you ever smelled the aroma of a burned wall wart around your printer, you should have a tell-tale sign of the problem. If you are licensed to operate a VOM, you can put your safety tech hat on and probe around after unplugging the thing... What the tech does is look for an impedance that is higher than expected from the power source end of the -LOOP- of wire, including that in the bed heater - even disguised as a circuit board, that is the closed circuit that is the heated bed et al. This is math: say 24 volt source to heater bed 100Watts bed means roughly 4 amps of power. A little more EE math and you get an impedance value that the system must be maximum ohm value. Very low ohms! And here is where degree of difference matters, because it could means exactly that, 4 minutes to heat the bed or 30 minutes if a wire is on the verge of breaking.

    Problem with the simple tech method using VOM is that you are not stressing the system. A current meter... a direct measurement will assure you how much jiuce is flowing into the bed. You know the source voltage so a current reading should tell you how many watts are being used to heat the bed. They even make non-contact current meters for quick diagnostic tests. Not in everyone's toolbox though. But you can buy current meters online at reasonable cost that can be spliced into the line. These are cheap DIY gadgets.

    I'm gonna bet that 20 minutes is a bit harsh for any bed heating wait time. You may have a power supply that is woefully inadequate! What's more likely is that you have a poorly attached bond in the wire somewhere. Not knowing this system, I can only say follow the big wires to the bed and see what may be wrong along the path. Burned connectors is an easy sign to notice; loose pin inside connector -loosely fitting connectors in general- is a huge impedance under load. Hence the need for a current meter to test. A wire that has frayed to only a few strands at the connector end of a wire, or a working pinch point in the bed movement. You can find these by carefully flexing wire and see if there is a weak kink somewhere. Next time you run the printer, put your finger there and see if it isn't getting warm.

    You could even do an input power analysis to see if each component is drawing it's reasonable share by comparing the AC input loads on the power supply. It is still about watts being drawn! You should be able to pick up ballpark figure on the difference between running with and without a heater bed just monitoring the AC input to the power supply. Again, if you have a way to read the current being drawn. You know the voltage... whatever your wall voltage is, 120 or 240 (115|230).

    And I'm sure there are other tricks. If I knew more about the way these are set up, I might have other things to look at but I'd start with a careful inspection. The fault is in a very simple loop that pushed quite a bit of juice.



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