Very slow bed heating

ixlix

Hi all,

I have a delta with a mains powered bed which has been working well up until now. Ive noticed that the bed now takes forever to heat up, at the rate of about 0.1° per second. It sometimes just stays at the same temp even though I can see the power (green on the temp graph) is full. It used to heat at the rate of 1-2° per sec. Nothing has changed on the printer harware/wiring wise and I have tried PID tuning etc. Im pretty sure its been set on PID heat manager for the bed, but the system uses an SSR and I have now read that Bang-Bang is better for that. Would the slow heating be due to a failing SSR? The light on the SSR still comes on when heating, but im stumped as to why its so slow.

Alex

Repetier

As long as you are on 100% output it is not relevant if you have bang bang or pid. It is constantly open. So SSR would be a good reason. You are just not getting full power into the bed while power is set to on. Can also be a broken or partially broken cable so resistance is higher. But sounds like hardware error. 

ixlix

Thanks for the info. When you say hardware error you mean the bed wiring or heater pad right?

I swapped in the SSR from another working printer and the behaviour is the same, very slow heating. I just tried heating the bed to 100° and so far its been going for 10mins and only at 46°. I know its a 10mm thick alu bed but it used to be faster than that. My 6mm alu bed reaches 100° in a couple of minutes.

I have a thermal fuse inline and attached tot he underside of the aluminium bed, so i checked that and thats fine.

I have another bed with mains heater pad on it so i will test that tomorrow.

ixlix

So i just measured the resistance of the silicone heater pad. Measring from the connectors on the leads its 321ohms. Being a 220V 800W heater pad that would make it that im only getting 160watts of power from it due to the resistance, hence the slow heat up.

So is it safe to say the heater pad is faulty?

Repetier

For a 12V bed 150 watt with 20x20cm would be good and heat within minutes, but with 800W I guess it is a bit bigger. For 800W resistance seem a bit high I guess, but I'm no electronic expert. But might in deed be the reason also I can not understand how it can loose so much resistance. If broken I'd expect nothing working. For higher resistance I'd expect some contact problems somewhere.