24V Upgrade to my Max V3
Posted: Tue Oct 04, 2016 5:00 pm
Most of this is copied from another thread. Just putting it here to help others.
After building my Max V3, I was surprised how weak the bed heating performance is in a stock config. Mine would never go over @95C without a washcloth on the bed. You can turn the power supply output voltage up to 14V and it will eventually hit 100C but still takes a long time. (That keeps you below the 15A bed heater fuse limit). I measured my Onyx with a high-end multimeter and it is 0.92 Ohms. Power measurements also bear out that number. That's a lot lower than I've read other places for the Onyx btw.
I ended up buying a 600W 24V PS, a Crydom 40A DC/DC solid state relay to drive the bed and a 20A 12V step-down regulator to drive everything else.
Turn the voltage on the power supply down to 20.5V to limit the bed heating to around 450W and make sure to put a fuse on that circuit. Now it will go from 25C to 100C in about 3 minutes.
DO NOT buy a Fotek or SHZE SSR, even with a heatsink, thermal paste and good airflow they will heat up and fail very shortly (I know from experience). When they fail, they fail in the "ON" state so it's a fire hazard. Luckily I was watching closely. They have far too high of internal resistance to meet their spec in any reasonable install. Get a MOSTFET-based one like a Crydom or Auber with an ON resistance of around 0.006 ohms or so.
I ended up buying a 40A Crydom from Digikey: https://www.digikey.com/product-search/ ... =CC1860-ND which doesn't even get warm during use (with heatsink and airflow), but I believe the much cheaper Auber 100A has similar impedance: http://www.auberins.com/index.php?main_ ... cts_id=288
I mounted the SSR on its heatsink in the front of the base, right behind the front panel. I cut a small hole in that panel so it, the power supply and the regulator get great airflow from the stock base fan. The regulator is slightly behind and to the right of the SSR. It seems to stay fairly cool during operation as well. The power supply is mounted in the stock location. It's slightly wider than the stock one, so you need to just screw it to the base plate,
The only down-side is that idle power (at the wall) went from 11W to 18W due to the new PS and the step-down regulator.
THese are the other parts I'm using:
Heatsink: https://www.amazon.com/dp/B00ARBA02A/re ... R+heatsink
Regulator: https://www.amazon.com/gp/product/B00BW ... UTF8&psc=1
Fuse holder: https://www.amazon.com/gp/product/B00NQ ... UTF8&psc=1
Power supply: https://www.amazon.com/gp/product/B019R ... UTF8&psc=1
Thermal pase: https://www.amazon.com/Zalman-ZM-STG1-S ... rmal+paste
I used a small terminal block to connect the 12V wiring to the output of the regulator.
The power supply seems to be working great so far even though it's a cheap one.
I used some #8 x 3/8" sheet metal screws to attach those parts inside the base plate.
I also blocked all of the air vents in the base plate with gaffers tape so the base fan won't draw the hot air out of my enclosure.
After building my Max V3, I was surprised how weak the bed heating performance is in a stock config. Mine would never go over @95C without a washcloth on the bed. You can turn the power supply output voltage up to 14V and it will eventually hit 100C but still takes a long time. (That keeps you below the 15A bed heater fuse limit). I measured my Onyx with a high-end multimeter and it is 0.92 Ohms. Power measurements also bear out that number. That's a lot lower than I've read other places for the Onyx btw.
I ended up buying a 600W 24V PS, a Crydom 40A DC/DC solid state relay to drive the bed and a 20A 12V step-down regulator to drive everything else.
Turn the voltage on the power supply down to 20.5V to limit the bed heating to around 450W and make sure to put a fuse on that circuit. Now it will go from 25C to 100C in about 3 minutes.
DO NOT buy a Fotek or SHZE SSR, even with a heatsink, thermal paste and good airflow they will heat up and fail very shortly (I know from experience). When they fail, they fail in the "ON" state so it's a fire hazard. Luckily I was watching closely. They have far too high of internal resistance to meet their spec in any reasonable install. Get a MOSTFET-based one like a Crydom or Auber with an ON resistance of around 0.006 ohms or so.
I ended up buying a 40A Crydom from Digikey: https://www.digikey.com/product-search/ ... =CC1860-ND which doesn't even get warm during use (with heatsink and airflow), but I believe the much cheaper Auber 100A has similar impedance: http://www.auberins.com/index.php?main_ ... cts_id=288
I mounted the SSR on its heatsink in the front of the base, right behind the front panel. I cut a small hole in that panel so it, the power supply and the regulator get great airflow from the stock base fan. The regulator is slightly behind and to the right of the SSR. It seems to stay fairly cool during operation as well. The power supply is mounted in the stock location. It's slightly wider than the stock one, so you need to just screw it to the base plate,
The only down-side is that idle power (at the wall) went from 11W to 18W due to the new PS and the step-down regulator.
THese are the other parts I'm using:
Heatsink: https://www.amazon.com/dp/B00ARBA02A/re ... R+heatsink
Regulator: https://www.amazon.com/gp/product/B00BW ... UTF8&psc=1
Fuse holder: https://www.amazon.com/gp/product/B00NQ ... UTF8&psc=1
Power supply: https://www.amazon.com/gp/product/B019R ... UTF8&psc=1
Thermal pase: https://www.amazon.com/Zalman-ZM-STG1-S ... rmal+paste
I used a small terminal block to connect the 12V wiring to the output of the regulator.
The power supply seems to be working great so far even though it's a cheap one.
I used some #8 x 3/8" sheet metal screws to attach those parts inside the base plate.
I also blocked all of the air vents in the base plate with gaffers tape so the base fan won't draw the hot air out of my enclosure.