Connections on sanguinololu board getting fried

Something that is happening too often on my printer is the four pin flat connector from my hotbed is melting the wires in the plug and sticking the plug to the sanguinololu board.

I am on my second board and I have had to change the plug again just in time to not melt the plug to the board.

The power plug from my computer power supply is also looking blackened both on the board and the plug but not melting yet.

My power supply is 500w computer power supply.

My hot bed temp is only 60c and the hotend is 230c.

So if its melting, it means to much current is running through those wires, you need to beef them

Or you can parallel the wiring if you have no thicker wiring, im not sure about the connectors you have, changing the wiring should help,
you might want to face the fan over the connectors if they still get hot after that..

id like to see a pic if you can

The sanguinololu is small and cheap, but the connector for the heatbed is underspec. They are simply not designed to take the current drawn by a typical heatbed. This is not just theoretical, many people have reported the same problem.

I think the only practical solution is not to use the on board MOSFET for the heatbed, but use an external relay or MOSFET driver.

Thanks for the replys.

I am using the same wire thickness for the hot end as the hot bed and the hot end connections are fine.

The hot end is running at 230c and the hot bed at 110c max so it doesn't make a lot of sense but I will beef up the wires on the hot bed tomorrow.

The connections on the sanguinololu are a 4 in line set but I only have 2 wires from my hot bed so not sure how to double the wires so looks like thicker is the way to go.

I have been using old computer wires that used to go to the hard drives for power so they are not up to the task.

The Sanguinololu hotend and HBP connectors have 2 pins for each end of the heated bed, split down the middle. You should use all four pins and double up the wires going from the connector to the HBP to ease the load on each of the pins. Though after doing this it'll likely exceed the rating for the connector pins.

I had the same problems and burned through a few connectors, and now I use the hot bed connector simply to trigger a 12V 30amp car relay that powers the bed straight off the PSU via the relay, bypassing the Sanguino alltogether . No more problems. (And I'm running at 16V)

@Damion

Are you finding that the heatbed heats better and faster at 16V? Mine takes about 20 minutes or longer at 12V. What PSU are you using for the 16V?

It's great, I'm using this PSU from ebay it's actually adjustable from 9.5v-16v.
My bed gets to 60c in about 45seconds and 110c in about 3-4min. (I have an oversized aluminum bed)

Edited 1 time(s). Last edit at 10/09/2013 09:36PM by Damion.

As a general rule, pin connectors get about 1A per pin max. Looks like you're drawing more than that. If you've got a good multimeter, it'd be worth hooking it up to measure the current when you're printing.

gregted Wrote:
-------------------------------------------------------
> Thanks for the replys.
>
> I am using the same wire thickness for the hot end
> as the hot bed and the hot end connections are
> fine.
>
> The hot end is running at 230c and the hot bed at
> 110c max so it doesn't make a lot of sense but I
> will beef up the wires on the hot bed tomorrow.

The temperature that each of these get to has nothing to do with your problem. The hot end only needs about 2A of current, but the heat bed needs around 12A. Therefore, the wire to the heat bed should be 6 times larger. Use a wire size of at least 18 gauge, for this current.

Most likely though, is that the contacts for the connectors are not rated for that current, and so they will heat up, and melt things. You may be better off soldering the wires directly to the board.

>
> The connections on the sanguinololu are a 4 in
> line set but I only have 2 wires from my hot bed
> so not sure how to double the wires so looks like
> thicker is the way to go.
>

Run two wires in parallel all the way to the heat bed. Just solder two wires to one terminal on your heat bed. This also spreads the current across more pins, which will reduce the current in each pin causing less heating in the connector.

Recall if you get bigger connectors you still have to reinforce the line between +12V and the +12V output to the heatbed.
"The pads and traces on the board are not robust enough to handle the high current involved when controlling the heated bed with the sanguinololu's dedicated mosfet"
[reprap.org]

I also went the route of not making my Sanguinololu switch the heat bed directly. In my case, the Sanguinololu switches a PNP transistor (didn't have a PMOS ) which in turn switches two NMOS (N-Channel MOSFET) on a separate board.
There's also the option of getting a beefier connector that fits on the board. I use this for my heatbed connector, and it fits in the Sanguinololu with no modification: [www.digikey.ca]〈=en&site=ca&KeyWords=A19452-ND

You can connect one side of the bed directly to the PSU and the other to a ring terminal fastened to the bed MOSFET's tab. That way you avoid the underrated connector and PCB tracks.

---

[www.hydraraptor.blogspot.com]

Thanks all for the replys.

I have not been printing for a while as the new board also melted and I got sick of buying boards. I will buy some new headers and resolder my board and see how that goes.

I have replaced the hotbed wires with much thicker ones so we will see how that goes.

I have attached pics of the old melted board and the new thicker wires on my new board. If that still gets hot, I might double up the wires to the hotbed.

I am interested in powering the hotbed directly from the power supply but not sure how to do that.

If I connect the hotbed directly to my power supply, how will I control the heat?

Have to set up reprap software all over again after my computer died and had to get another one. The fun goes on...