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| reprap:anet:a8:improvements:understanding_my_heatbed [2018/12/30 09:43] – [Investigating other effects] cj_elec_tech | reprap:anet:a8:improvements:understanding_my_heatbed [2018/12/30 09:58] – [Heat-bed Power] cj_elec_tech |
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| {{ :reprap:anet:a8:improvements:mypicture15.gif |}}. | {{ :reprap:anet:a8:improvements:mypicture15.gif |}}. |
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| ==== The power supllied to the heatbed ==== | ==== Heat-bed Power ==== |
| As the curves where very similar I investigated if the controller was ajusting the PWM duty cycle and therefore the curves where a controler effect and not a thermodynamic. The voltage was a flat line on the osziloscope, therefore this theory was discarded. | As the curves were very similar, I investigated if the effect was caused by the controller rather than being a thermodynamic effect (the controller adjusts the PWM duty cycle - and thus the curve). The voltage was a flat line on the oscilloscope, therefore this theory was discarded. |
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| Than I measured the current and observed that it drops with increasing temperature. | Then I measured the current and observed that it drops with increasing temperature. |
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| {{ :reprap:anet:a8:improvements:mypicture2.gif |}} | {{ :reprap:anet:a8:improvements:mypicture2.gif |}} |
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| If the resistance is calculated by divinding the voltage through the current this leads to the following resistance{{ :reprap:anet:a8:improvements:mypicture3.gif?direct&400 |}} | Resistance is calculated by dividing voltage by current - this lead to the following resistance{{ :reprap:anet:a8:improvements:mypicture3.gif?direct&400 |}} |
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| And this gradinet fits nearly to the gradient expected for cupper with an temperature coefficient of appximatly 0.0039 1/K | This gradient nearly fits the gradient expected for copper with an temperature coefficient of approximately 0.0039 1/K |
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| This is probably also the reason why there are values of 1.2 to 1.6 Ohms mentioned in some forums and sites for this heat bed. | This is probably the reason why there are values of 1.2 to 1.6 Ohms mentioned in some forums and sites for this heat-bed. |
| ==== Simulating the heat bed ==== | ==== Simulating the heat bed ==== |
| In order to undertstand the heat bed behavior in more datail I made a {{ :reprap:anet:a8:improvements:warm_up_2.xlsx |heat bed simulator}} in excel (dispite I don't like to this software for simulations). It fits quite well to the measured data, therefore it seems to be not so bad. But keep in mind that it is a model and not the reality. | In order to undertstand the heat bed behavior in more datail I made a {{ :reprap:anet:a8:improvements:warm_up_2.xlsx |heat bed simulator}} in excel (dispite I don't like to this software for simulations). It fits quite well to the measured data, therefore it seems to be not so bad. But keep in mind that it is a model and not the reality. |