What’s the controller board used by the K8200? Is it 3Drag?
Where can I find specs for it?
I’m specifically wondering about max current that can be supplied to the fan, heatbed and extruder (thinking of changing the fan and the heatbed). Also I understand the PSU is 15V, but is it possible to somehow use 24V for the heatbed?
Also (possibly material for a different thread), is there a maximum temperature that the supplied heatbed can endure?
Also is there some kind of regulator to reduce voltage for the fan down to 12V? Or is it driven by 15V as well?
Just checked the fan, it’s fed 15V, so overvolted by 25% :->
Huh. Wonder if that’s safe…
[quote=“uukgoblin”]Just checked the fan, it’s fed 15V, so overvolted by 25% :->
Huh. Wonder if that’s safe…[/quote]
To fit a 24v heatbed it’s better to use a power expander (circuit can be found here on the forum) or a simple
relay circuit to switch the 24V supply controlled by the heater output.
Both is simple and cheap.
I used a relay.
The Board is the 3drag controller.
Schematics are here : reprap.org/wiki/3Drag_controller
cheers,
Christian
Thanks again!
So if I’m reading this right, the heaters and the fan are all controlled by T1-T3, which are all BUK6215-75C mosfets. Datasheet at nxp.com/documents/data_sheet/BUK6215-75C.pdf says it has 57A drain current, so there should be plenty of room for more power - I guess I’m only limited by the PSU.
So I’ll have to check how much current the printer takes in current config with everything on, and then subtract that from the 6.67A rating of the PSU and I’ll know how much stronger a fan and bed I can connect.
I guess I’ll end up using a separate PSU for the heatbed, but it’s good to know I can probably ramp the fan up to 1A.
[quote=“uukgoblin”]Thanks again!
So if I’m reading this right, the heaters and the fan are all controlled by T1-T3, which are all BUK6215-75C mosfets. Datasheet at nxp.com/documents/data_sheet/BUK6215-75C.pdf says it has 57A drain current, so there should be plenty of room for more power - I guess I’m only limited by the PSU.
So I’ll have to check how much current the printer takes in current config with everything on, and then subtract that from the 6.67A rating of the PSU and I’ll know how much stronger a fan and bed I can connect.
I guess I’ll end up using a separate PSU for the heatbed, but it’s good to know I can probably ramp the fan up to 1A.[/quote]
For the fan this ist surely true, but beware if you put a high am Heatbed on.
I don’t think the PCB tracescan handle much more current than the stock heatbed draws!
The MosFet’s sure can, but not the board!
Hmm, good point, will keep in mind!
Now I have an evil plan of just connecting about 10x 100ohm 10w resistors (relatively cheap from Maplin, only 0.89 GBP each) in series straight to the 240v socket… Switch them on/off with a relay perhaps. That’d avoid the cost of an expensive high-power power supply…
The only problem I can think of is how to insulate the resistors’ terminals, as they’ll probably get up to 120 deg C and more :-> And I really don’t want unisolated 240V flying below my heatbed 
[quote=“uukgoblin”]Hmm, good point, will keep in mind!
Now I have an evil plan of just connecting about 10x 100ohm 10w resistors (relatively cheap from Maplin, only 0.89 GBP each) in series straight to the 240v socket… Switch them on/off with a relay perhaps. That’d avoid the cost of an expensive high-power power supply…
The only problem I can think of is how to insulate the resistors’ terminals, as they’ll probably get up to 120 deg C and more :-> And I really don’t want unisolated 240V flying below my heatbed :-D[/quote]
What wattage do you want to use for your heatbed?
I have my stock k8200 Heatbed 24V powered over a 36€ notebook style 24V/5A supply and a relay.
So, not that expensive at all…
I want to be able to print ABS, so my guess is I need about 90-100 deg C.
Not sure what the heat losses are but I definitely need more than the stock provides (which by my calculation is about 45W as the heatbed resistance is about 5 ohm… some say 6, not sure). Having 10x 100ohm resistors in series would give me 58 watts of extra power.
The laptop supply idea is interesting, or perhaps I could use an old ATX desktop PSU… So many options to choose from
[quote=“uukgoblin”]I want to be able to print ABS, so my guess is I need about 90-100 deg C.
Not sure what the heat losses are but I definitely need more than the stock provides (which by my calculation is about 45W as the heatbed resistance is about 5 ohm… some say 6, not sure). Having 10x 100ohm resistors in series would give me 58 watts of extra power.
The laptop supply idea is interesting, or perhaps I could use an old ATX desktop PSU… So many options to choose from :-D[/quote]
With my 24V/5Amp supply and a small 3mm cork sheet under the heatbed pcb i get my stock heatbed easily to 100°C.
Even with a glass plate on top.
cheers,
Christian
Thanks, bottom cork as isolator sounds like a good plan 
That’s what I’ll go for then. Found a 24v / 5a laptop supply for 13 GBP on ebay, gonna add a power mosfet through an optocoupler (not sure if I want the relay constantly clicking on/off at 4 amps) and that should do it.
[quote=“uukgoblin”]Thanks, bottom cork as isolator sounds like a good plan
That’s what I’ll go for then. Found a 24v / 5a laptop supply for 13 GBP on ebay, gonna add a power mosfet through an optocoupler (not sure if I want the relay constantly clicking on/off at 4 amps) and that should do it.[/quote]
Ill make the mosfet circuit too.
I was just too lazy till now, and the relay laid around somwhere 