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Expanding Taz 4, need a little info

Posted: Fri Aug 17, 2018 9:01 am
by gghouck
My plan is to double the Y axis on my Taz 4. I'm getting ready to make the bed heater but need some help. So my plan is to make the heater1.6 ohms maybe less, meaning it will draw somewhere around 16 amps, which I believe is a bit much for the Ramboard (I don't recall which version of the board I have). So the questions are: Can the board handle that amount of current? If not, is there a mod I can to to it to make it able to (I can replace board components), and if not, is there a way of controlling the current from an external PSU to the new heater? Is the power to the bed from the Rambo actually metered or is it simply an on/off situation where a solid state relay would suffice? The PSU has already been upgraded to a 500 watt unit so I believe I'm good there but I've even entertained going up to a 30volt PSU to get the wattage to the bed heater up without too much current, but do not know what else will end up with 30 volts (steppers, hotend). Any help will be appreciated

Re: Expanding Taz 4, need a little info

Posted: Sat Aug 18, 2018 5:55 am
by kmanley57
I think if you are going to double the bed size you are needing to double the watts you need for the bed. So a 110v bed is needed for that many watts of power with less current requirement. Otherwise it will take a long time for the bed to reach a good temperature if it ever does. Or you are going to only print with PLA and flexible filaments.

I do not think the control board can handle the amount of amperage you would need for a 24-28 volt heat bed. Plus you would need larger less flexible bed wires to carry the higher current.

Re: Expanding Taz 4, need a little info

Posted: Sat Aug 18, 2018 7:48 am
by gghouck
The stock bed takes 10 amps, I know this because my PSU has a built-in ammeter/volt meter and , so ~20 amps would heat the bigger bed at the same rate. Bigger wiring is the easy part since I am building the bed heater.
So the questions still remain: If I go up to a 30 volt PSU, will that effect the power to the steppers or hotend and what if anything will I need to adjust?
No matter if I got to 30 volts or 110 volts, how do I go about controlling the power to that? Can it be done with a simple solid-state relay?

Re: Expanding Taz 4, need a little info

Posted: Sat Aug 18, 2018 8:03 am
by kmanley57
It pulls more like 14 Amps, as it is a PWM output that pulses averaging 10A on the probable RMS meter.

360 Watt bed on 24 volts equals ~15 Amps a reason it has a slower blow Auto fuse. That helps it dissipate the surge heat created and not blow fast, but will possibly blow over time/use.

Re: Expanding Taz 4, need a little info

Posted: Sat Aug 18, 2018 8:21 am
by gghouck
So, ALL my original questions still remain.

Re: Expanding Taz 4, need a little info

Posted: Sat Aug 18, 2018 11:01 am
by kmanley57
gghouck wrote:
Sat Aug 18, 2018 8:21 am
So, ALL my original questions still remain.
#1 Not really, but you need to supply more than that at the max voltage the board can handle.
#2a No.
#2b Yes but it probably requires a external hardware relay and possibly firmware changes to change control response times.

The bed F.E.T. on the board can handle around 50 volts, but the other control board components can not.

I would not recommend use of a 110 volt heat bed, but for what you wish to do you would need to.

Re: Expanding Taz 4, need a little info

Posted: Mon Aug 20, 2018 11:13 am
by gghouck
Thank You