Slow getting to 110C bed target on 10" i3v

[JimG]

Not sure what has changed, but it is now taking a really long time to get my bed to 110C for ABS printing. I am talking 30 minutes to an hour, or forever! (see below):

A few observations:

1. The output at the Meanwell 350W PSU measures 12.00V under full load, so that does not seem to be the bottleneck.
2. At the relay board, the supply voltage has dropped to 11.65V. So I am losing 0.35V in the 16 AWG wires between the PSU and the relay board.
3. If I place a sheet of white copy paper over the glass on the bed, it heats in 20 minutes or less. I think it is blocking the drafts from the fan. (There is a sheet of cardboard below the heater).
4. The fan on my Hexagon hot end seems to play a major role in this. Once I left the extruder parked near the center of the bed, where the fan drafts hit more of the bed, and the temps topped out at 93C.
5. With the extruder in the home position the fan has less influence.
6. Have not measured the voltage drop across the lighter gauge supply wires from the relay to the bed heater, but based on the warming of the wires I think a fair amount of energy is being lost there, too.

My solution has been to use 105C for ABS, which is working fine for my prints. The extra time needed to go from 105C to 110C is significant.

I think I would have to change the fan mount on my hot end for 110C to be a routinely usable bed temp.

Anyone else have a similar experience?

Jim

[printbus]

I've been curious - can you read wire gauge markings on the wires going to the heat bed? I know my 8-inch heater uses 16 AWG, and I've wondered if it's the same on the larger heater. 16 AWG is on the small side for handling the 17-18 amps that the 10-inch heat bed requires. Assuming you have the same 0.35v drop from the relay to the heater, your 200W heat bed is only seeing about 175 watts.

Is there a chance that the bed thermistor is resting on the cardboard insulator below the heat bed? That could be causing the bed thermistor to read low.

If you install the hex hot end fan so that air is pushed into the hot end, people have noticed it tends to create drafts on the bed below the extruder. Reversing the fan helps defocus these drafts but it doesn't eliminate them. Clough42 has a cooling system that sends the hot end airflow up from the extruder, eliminating any concern with the hot end airflow.

[JimG]

The heater lead wires are only 18 AWG, which is really too small. I probably will solder in one or more parallel leads. I think replacing with a single heavier gauge wire might cause it not tolerate the movements?

The thermistor readings are good. During my build, I stuck a fine wire type T TC on the underside of the bed to use for confirmation of the thermistor readings. The TC responds much faster to the heater, but always reads within 4C of the LCD display.

Jim

[printbus]

The heater lead wires are only 18 AWG, which is really too small. I probably will solder in one or more parallel leads. I think replacing with a single heavier gauge wire might cause it not tolerate the movements?

The thermistor readings are good. During my build, I stuck a fine wire type T TC on the underside of the bed to use for confirmation of the thermistor readings. The TC responds much faster to the heater, but always reads within 4C of the LCD display.

Jim

Oh, man. 18 gauge is definitely too small IMO. What I've recommended a few times is check into your local R/C hobby store and ask if they have silicone wire. It's ideal for the bed wires that are subjected to a lot of flex. The silicone insulation is more flexible than the standard PVC jacket, and the wire is made up of a significantly larger number of finer strands that will keep it highly flexible. One source says, for example, that their 12-gauge silicone wire consists of 680 strands. Some neighborhood R/C stores and online places sell it by the foot, so you only have to buy what you need. It can be pricey if you have to buy a prepackaged amount like 10 feet and only need a couple.

I've also suggested, simply for good measure, that once the size for the wire to the heat bed is chosen, use the next larger gauge wire for the fixed wire between the heat bed relay and the power supply. Like you said, it's also possible to double up on smaller gauge wires. There's nothing wrong with that other than the increased bulk of the extra insulation.

Now I'm wondering if my heat bed might have actually had 18-gauge wires before I swapped them out with some of the silicone stuff I had on hand.

If you have the chance, measure the voltage at the bed itself so we can calculate how much power the bed is actually getting.

[Stigern]

I have a trick of putting a cloth piece over the bed while the printer is doing its warming up process :P

I think I have 16AWG silicone wires to the relay. So changing the wires to the bed too? Seems likely that they are too small.

[Drone]

For my i3V 10 where I put the clip for my glass makes a major difference. When I moved my clips to the front and back of the printbed it took forever to reach 110c, and when I put them back on the sides it only takes a few minutes to heat to temp. YMMV, but it made a big difference for me. Even where I put the clips on the sides makes a difference.

[JimG]

I have a trick of putting a cloth piece over the bed while the printer is doing its warming up process :P

Great idea. Before I developed advanced CRS* that would have worked for me, too ;-)

Jim

*Can't Remember S*&^

[JimG]

For my i3V 10 where I put the clip for my glass makes a major difference. When I moved my clips to the front and back of the printbed it took forever to reach 110c, and when I put them back on the sides it only takes a few minutes to heat to temp. YMMV, but it made a big difference for me. Even where I put the clips on the sides makes a difference.

Interesting. I recently moved 1 of the 4 clips a little further from the middle of the board. Would not have thought that would affect heating of the bed!

Jim

[JimG]

...What I've recommended a few times is check into your local R/C hobby store and ask if they have silicone wire...

...If you have the chance, measure the voltage at the bed itself so we can calculate how much power the bed is actually getting...

I've got some 14AWG R/C wire on the way. I thought the 14AWG would be a little more flexible, plus I don't have any crimp fittings or ferrules that will fit the 12AWG.

Plus, I think I will just run the GND wire direct to the PSU from the heater. The relay board only switches one side of the circuit. That will save a few feet of wire run.

When I make the changeover I will try and remember to take a few voltage readings. The solder joint where the lead wires connect is hard to get to without a disassembly.

Jim

Jim

[old man emu]

Jim,
Go to your local Radio Shack (or equivalent). Buy a 5 Amp car horn relay and some 14AWG multi-strand wire. Go home (Straight home, dammit!)

Run the 14 AWG from your power supply to the heat bed via the relay. It is only the +ve wire that needs to be cut so that it is can have the relay connected into that path.

Use the 18 AWG wires to connect the other poles of the relay to the RAMPS board.

Now the RAMPs board will switch the relay on to allow free flow of current along thick wires from the PSU to the bed.

DO NOT - repeat - DO NOT fit a relay similarly between the RAMPS board and the extruder heater resistor unless you want to let the smoke out of the components on the RAMPS and Arduino boards.

Then go to your local bar and buy a beer for Old Man Emu.

Have a look at this: http://3dprintboard.com/showthread.p...formance/page2

OME