Hello everyone, I’ve been very curious for time now but have very little knowledge when it comes to circuitry or electrical engineering in general, so I have a question for you. Could the alligator run four heated beds, all of which I’d merge to being one big heated bed, with a talker build height, this custom printer could be huge in comparison to a normal prusa I3. I’d be building it all from scratch, custom so it’ll be a bit of a task. I just don’t know if it’s even possible. Thanks again everyone!
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I don’t know specifics about the Alligator, but it looks to have a single DC bed output with a single MOSFET. That almost certainly won’t be enough to drive the 40-50 amps you’d likely need if you had 4 MK2 beds running in parallel over 12v. Your best option would likely to be to use a solid state relay with its own power supply, or even better, use 110v/220v AC silicone heaters and a corresponding AC solid state relay to avoid trying to find a DC power supply that can supply the enormous current you need for 4 beds.
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Totally Agree.
Don’t bother with normal mk2 beds in such a size. The best option is to use Solid state Relay and Silicon heaters.
You will need DC to AC Solid State Relay (SSR) and AC silicon heater pad (you will find the sizes you need like 300x300mm ) (one/relay). They heat up much faster than mk2 beds and usually include a 100k thermistor inside.
Keep in mind that it might be a good idea to include a switch on the SSR-s so if you don’t need all the print surface heated than you can switch off the heaters witch not required.
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I have a coreXY in build 90% functional that uses 4 200mm sq heated beds for a total print area just over 400mm sq or roughly 17in on each side. Height is only limited by the rigidity of the frame. I run my beds from 18v so you can either run to beds in series and the pair in parallel drawing about 500w or you can run two beds in parallel and then in series with the next two beds in parallel; 1000w. These are 12v beds. At 500w you can reach PLA printing temps, at 1000w you can reach ABS printing temps. That will be 10A draw from a 120v outlet just for the beds. I am currently wired for 500w myself as printing an abs print that large with the issue of warping is unreasonable. Ian running off board (externally mounted) FETs to overcome the large current draw as the single one on a ramps board is not enough.
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Yeah I primarily print abs, thank you all so much for the replies and ideas! When I referred to the alligator board I meant it with the upgrade attachment as well, if that makes any difference. I’m hoping to do it the most cost effective way as possible, may I ask what the price ranges for your alternatives are?
If you had multiple power supplies or one very large one you could probably get away with it but do you need a heated bed at all? Some types of plastics like ABS don’t require one. PLA does but I’ve read that you can print without it if you use things like blue tape and/or hair spray. Then there’s the option of making your own. I’ve seen Indestructibles on this.
Bruce
Ummm, sorry, but this is completely wrong… You ABSOLUTELY need a heated bed for ABS parts of any size… It has way higher warpage than PLA (1.5%-2.0% vs. 0.4%) and will peel off the buildplate if not heated (to between 90 and 110 degrees C) and coated with some film or adhesive.
Conversely, PLA almost doesn’t need a heated buildplate, but it becomes necessary for larger parts (typically a bed temp between 30 and 50 degrees C is good).
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If you want very big heatbed , you can try this solutions : http://www.instructables.com/id/Mega-Prusa-i3-Rework-8-x-Build-Volume/?ALLSTEPS
I didn’t try it but i’m on my way to build one.
I stand corrected and defer to you since I have no experience with ABS and have only been a 3D’er for a couple of weeks.
Thx
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Don’t think so you will need that expansion board, as i have just checked they have 3 connections on it for hot-ends and not heat beds.
For the prices, please consider that you will only need a small 12V or 24V(10A max.) power supply for motors and hotend. As the silicone heaters we recomend uses normal AC power so no power supply required, you can save a lot of money avoid to purchase a 1000-1200W 12/24V power supply.
Here is an example: 300x300mm 23 USD.
http://www.aliexpress.com/item/1pcs-silicone-heating-pad-heater-220V-600W-300-300-mm-for-3d-printer-heat-bed/32591046539.html?spm=2114.30010308.3.115.Ii2oiQ&ws_ab_test=searchweb201556_9,searchweb201644_1_505_506_503_504_502_10001_10002_10016_10005_10006_10003_10004,searchweb201560_1,searchweb1451318400_-1,searchweb1451318411_6450&btsid=acea654a-586b-4d75-9c4f-c3af1203c21d
The Solid State Relay (SSR) is DC to AC type (DC voltage from the alligator board will switch on the AC voltage for the heater pad) 3 USD
http://www.aliexpress.com/item/New1pc-solid-state-relay-SSR-25DA-25A-actually-3-32V-DC-TO-24-380V-AC-SSR/32436489770.html?spm=2114.30010308.3.1.SN0269&ws_ab_test=searchweb201556_9,searchweb201644_1_505_506_503_504_502_10001_10002_10016_10005_10006_10003_10004,searchweb201560_1,searchweb1451318400_-1,searchweb1451318411_6450&btsid=2a47ebe4-b231-4f7a-8016-25a7032878be
I’ve successfully manage to plug 3 cheap mk2 pcb like this one:
On a normal Ramp pcb
http://reprap.org/wiki/Prusa\_i3\_Rework\_Electronics\_and\_wiring
I’ve simply connected a 15A SSR on the 12V output of the Ramp that normaly drive the heat bed
This SSR now drives a 72v Transformers
And the transformer 72V AC is wire to heat bed in serie on the 24V input (Yes in AC)
Has been running great for a year or so
PRO: Running high voltage Alow for small curent and more managable wire size
CON: Can’t turn bed On or Off individualy
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I am with everyone who suggested an ssr relay to control your bed current to avoid burning up your printer controller, I’ve even heard of people using an automotive relay with success but it will be noisy when it switches on and off, will also require bed heating to be put in bang bang mode instead of pid controlled if an automotive relay is used
dmyers7
13
Solid state relays (nothing more than just a fancy FET) is ok but I avoid mechanical relays like the plague on something like this because of the currents and how often it needs to switch on and off. The most common failure for a mechanical relay is for the contacts to burn closed dumping 100% current to the board until you find it and hopefully not in smoke; this is especially true if the contacts are underrated. Please be careful. There are extremely affordable 100A FETs out there and you can gang them. Cool them with a fan if so desired. I am running one now @ 27A no fan for the 500W heated MK2 pcb beds as described above (4 qty). Works fine and affordable. Will use two if I decide to go to the 1000W setup. I like the idea of 72v AC for lower current, just not in love with 72v AC on an exposed component like a heated bed. Be careful of scratched exposed traces and lead wires when the bed is live. 18v dc is bad enough, but not dangerous, 72v AC could get dicey if your not careful.
zx81
14
I actually thought about doing this myself but then decided against it, as you would probably need to ether get one huge custom made heat pad (silicone/ PCB) or make some sort of temperature circuitry to keep all 4 heaters at a even temperature. its far simpler to cut your 3d files into smaller sections and glue/bond them together.
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Yes I can vouch for the fact that printing abs makes a heated bed necessary. I’ve printed in pla many times before and am actually leading an effort to do some experimentation with pla and ambient room temperature, it appears the cooler the room is, the more the pla sticks
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dmyers7
16
The cooler… Interesting. Is that with a heated bed for the PLA? (Sorry to hijacked)
Actually it’s just with painters tape. I’ve been trying with the bed at different temperatures, having it at 40-55*C makes such a strong bond though that often times I can’t even remove the print from the bed without having to redo the tape. To such an extreme that the one time I literally picked up the entire printer via the print and had to have someone else force it back down to remove it. Still trying to find the balance between it all
dmyers7
18
Here too. Except when the PLA print is so big (I.e. On my 400x400mm bed before I had heat enabled, the PLA pulled up the 3m blue tape from the glass bed and warped.). Heat and hair spray. And then a razor blade. Same print went great.
A lot of this could be your nozzle offset for the first layer as well. Try printing a calibration cube (here’s one: 40mm Cube Test Object by bre - Thingiverse) and making sure it’s actually the height it’s supposed to be. If it’s a little off, either lower your bed a bit, or correct for it in your slicer’s gcode offsets and give that a shot!
And if you want a way lower maintenance coating than painter’s tape, try purple Elmer’s glue stick! It works more consistently, is friendly with a better range of temperatures, is simple to recoat, and washes right off! Just make sure you apply it to the whole bed and you’re set 
If your printing Pla on a heated glass bed… My advice is take off the blue tape, clean the hot glass with cider vinegar and print on the clean glass (works every time with no mess) if your bed is heated aluminum I suggest printing on heated kapton tape washed with rubbing alcohol. I’ve never had to use glue or any other messy techniques
Only use use the blue tape on non heated beds as the adhesive will soften and release from your bed at printing temps.
Cheers
