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Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 6:55 am
by JaseGillUK
Hi all,
Issues with my 24v Heated bed. Have set it up as per the picture below but have the same issue whether I use 12v or 24v beds (have a V3 24V Bed as well as the standard bed that came with the printer).

So what happens is:
1. Switch on Printer,
2. Switch on Switched 24V PSU,
3. Set a temperature.... Nothing happens.

If I either then switch the 24v supply off and on again or I disconnect the bed and then reconnect then the heat comes on, but it wont go off, it just stays there until I switch off the 24v supply again to stop a runaway heated bed.
If I test it with a voltmeter at the end of the 24v supply it switches on and off as I set heat on and off. Really strange behaviour.
I have tried swapping the SSRoutput so that it either interupts + or - lines and it makes no difference.

I'm completely flummoxed now and wondering if anyone has any ideas?

Its set up like this (though bed can be either 24v or 12v one makes no difference if I swap them around).

Edit: PSU is this one: ... UTF8&psc=1

SSR is this one: ... UTF8&psc=1

Thanks Tincho85 for the diagram.

Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 7:52 am
by morgandc
Is the Rambo activating the relay reliably? If you put an ohm meter on the output, can you activate/deactivate the relay many times without any problems? I would start with trying to isolate which side of the relay the issue is on without the load on the output. I haven't played with board/chip outputs in a long time, but I could imagine some situations where the output on the board has to have a certain load to stabilize and the relay may not be providing enough of a load.

Just shooting in the dark.


Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 8:06 am
by JaseGillUK
Hi Dwight,
I am seeing a steady 12V at the SSR input.
The LED On the SSR is also lighting and goes off at the set temperature too.
So, I don't think its the input of the SSR that is the issue sadly.

Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 8:15 am
by JaseGillUK
I have only just noticed.
My SSR is DC in to AC Out. I think that might be the issue.
Looks like ordering a DC -> DC one and seeing if that fixes it :)

Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 8:51 am
by morgandc
That's not something I would have thought of. I will be watching to see what you figure out.

Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 9:34 am
by mhackney
PLEASE PLEASE PLEASE all. Firstly, SSRs are really a GREAT way to go to power your beds. BUT PLEASE READ THIS: How to Choose an SSR to Drive Your Bed

and this: !!!! DANGER DANGER !!!!


And NOTE, it is not a question of simply greatly increasing the amperage specs of the SSR, it's the voltage DROP across the terminals that produce HEAT that WILL start a fire.

Re: Faster Heated Bed Issue

Posted: Sat Oct 22, 2016 2:04 pm
by JaseGillUK
Not the one I used anyway.
To be honest will be keeping an eye on the replacements.
I have order 2 different ones, both from reputable suppliers (significantly more expensive too) and both supposedly handle 60 and 100 amps respectively so hoping now I have a proper DC to DC on the way it'll be fine.
Off travelling with work to Singapore for a week or so so wont be able to do anything until then so will keep all informed.

EDIT: Just realised one I have ordered is the Auber you recommend so that'll be the 1st I try.
DC to DC in the UK really hard to find and prices vary £50 to £100. Given the Auber in the US is <$20 I don't understand the pricing here.

Re: Faster Heated Bed Issue

Posted: Sun Oct 23, 2016 9:16 am
by JaseGillUK
I changed the SSR to a DC to DC one. 3-32V in 5-110V out and rated to 60A. Its this one: ... UTF8&psc=1

Different issue. SSR still comes on buy there is no heat at the bed.
Checked all connectors and 24V is being provided (23.7) but there is no heat at either the 12V or the 24V beds.

Could it be there isn't enough load on the circuit for the supply to provide enough current?
I'm at a total loss now and don't know where else to look. What else can I do to test the circuit is providing correct voltage and current at the bed?

Re: Faster Heated Bed Issue

Posted: Sun Oct 23, 2016 9:32 am
by morgandc
So you can measure 24v across the solder points on the bed itself?
What is the amperage going to the bed? You can put an amp meter inline with the bed, make sure the range is appropriate so you don't blow a fuse in the meter.
What is the resistance across your bed heater? (disconnected from the power supply)

If you have a constant 24v getting to the bed, it seems like either your bed heater is dead (0 ohms open circuit) or that the load isn't appropriate for the 24v supply (check the specs).


Re: Faster Heated Bed Issue

Posted: Sun Oct 23, 2016 9:57 am
by JaseGillUK
Measured across solder points on the bed I get 0V when they are connected to the Rambo though I get 11.27V so close enough to 12v not to matter.
The Resistance of both beds is around 1.2 ohms.
Not measured the amps running through it yet as I only have a 10A Amp Meter so need to get one that can measure larger loads.
Both beds heat if connected to the Rambo so I don't believe they are blown.

The PSU itself is a generic 24V one from Amazon here: ... UTF8&psc=1

It says its 24V and rated to 25A, and 600W but that's all I can find out about it. Starting to wonder if that is the source of the problems though...

Re: Faster Heated Bed Issue

Posted: Sun Oct 23, 2016 10:17 am
by morgandc
If you are getting 0v across the bed when connected to the SSR/24 volt power supply, no power is getting to the bed, the amps will be 0. (Voltage=Current x Resistance)

Can you hook the 24v power supply directly to the bed bypassing the SSR? You wouldn't want to leave it on for long (assuming it works), but you should be able to measure 24v across the bed if the power supply is working. If the bed works on 12v/Rambo it is a known good still. If you connect only the bed to the power supply and have 0v, either the power supply isn't compatible with the load, the PS is miswired/misconfigured, or bad.

Re: Faster Heated Bed Issue

Posted: Sun Oct 23, 2016 4:42 pm
by Noircogi
When on, the voltage across the SSR should be nearly zero.
If you have 23.7V at the power supply and zero at the bed, then either you have a bad connection somewhere or your SSR is bad.
Measure the voltage across it. If you have a good one like a Crydom or Auber it will have less than about a 0.2V drop while on.

If you're measuring full voltage across the SSR and the LED on the SSR is on, then the SSR is bad.

Re: Faster Heated Bed Issue

Posted: Sat Oct 29, 2016 1:56 pm
by JaseGillUK
Its fixed. A new Fotek SSR 100DD and it works as advertised.
Yet to stress test it but it comes on when the bed requests it and goes off when its up to temperature.

Now to stress test the Fotek and the PSU along with the new 24V bed.
Thanks for everyones help, such a friendly, useful forum here.