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Oil Filled Radiator as Hydro Dump Load W/ Midnite Classic 250 PWM Relay control & Solid State Relay

Darkstar

Rain Wrangler
Joined
Dec 31, 2019
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I converted an old oil filled radiator heater to be a dump load for our hydro/solar system. It dumps excess power as heat into our A=Frame greenhouse. I'm using the Midnite Classic 250 internal relay control along with a solid state relay to dump the excess power via PWM as the battery gets charged up. Got it working, still working on making it pretty...

 
Interesting, I didn't realize they just use hot water heater elements in the bottom of those oil filled column heaters.

The only problem with converting them to low voltage DC is your going to have a lot of amps traveling some distance around your greenhouse.
 
I have used one of those as a dump load to heat. Most of these have dual elements and if tied together this will dump 400W at that voltage. Although rated at 1500W at 120V, I doubt they are designed to work at that level unless the room is extremely cold. Note you have no thermal cutoff on the unit. At 370W I notice that the fins are no longer safe to touch at moderate room levels. It's your show, but I would be careful how much power you put into this. If I remember from other posts, adapting these to a standard water heater from metric is a pain. Using two in parallel with standard heater element is a better option. I have several of these picked up from trash day ot at garage sale for $2. The control system for these fail quite a bit and they can always be found thrown out.
 
I have used one of those as a dump load to heat. Most of these have dual elements and if tied together this will dump 400W at that voltage. Although rated at 1500W at 120V, I doubt they are designed to work at that level unless the room is extremely cold. Note you have no thermal cutoff on the unit. At 370W I notice that the fins are no longer safe to touch at moderate room levels. It's your show, but I would be careful how much power you put into this. If I remember from other posts, adapting these to a standard water heater from metric is a pain. Using two in parallel with standard heater element is a better option. I have several of these picked up from trash day ot at garage sale for $2. The control system for these fail quite a bit and they can always be found thrown out.

The threads in the unit I converted were standard NPT. I used a standard brass 1 1/4" to 1" reducing bushing and it threaded in perfectly. I did have an issue with a minor leak at the threads but fixed that with some high temp liquid gasket in a tube by permatex...
 
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Interesting, I didn't realize they just use hot water heater elements in the bottom of those oil filled column heaters.

The only problem with converting them to low voltage DC is your going to have a lot of amps traveling some distance around your greenhouse.


The heater is pretty close to the battery. 18 amps over 10' of AWG10 wire is all.
 
I have used one of those as a dump load to heat. Most of these have dual elements and if tied together this will dump 400W at that voltage. Although rated at 1500W at 120V, I doubt they are designed to work at that level unless the room is extremely cold. Note you have no thermal cutoff on the unit. At 370W I notice that the fins are no longer safe to touch at moderate room levels. It's your show, but I would be careful how much power you put into this. If I remember from other posts, adapting these to a standard water heater from metric is a pain. Using two in parallel with standard heater element is a better option. I have several of these picked up from trash day ot at garage sale for $2. The control system for these fail quite a bit and they can always be found thrown out.

I had some concerns about throwing out the thermal cutoff. Have been watching it closely. It has been taking a full 1000 watts for 6-8 hours on sunny days with no noticeable issues so far. Seems to be operating at temps similar to the days it was used as an AC heater...
 
I had some concerns about throwing out the thermal cutoff. Have been watching it closely. It has been taking a full 1000 watts for 6-8 hours on sunny days with no noticeable issues so far. Seems to be operating at temps similar to the days it was used as an AC heater...

A vendor of DC equipment put out a video of what happens when AC switches and breakers are used for DC. In his video, one just burned continuously. (I have my suspicion he designed his DC source to make this a good marketing video for his product.)

"thermal cutoff" - thing it'll actually cut anything off in your DC application?
"via PWM" - maybe that'll save the day. But does it every reach 100% on?

If you've salvaged any of these heaters, you could conduct a test where you overheat the cutoff and see if it actually does what you want, vs. just dissipating several hundred watts itself. Perhaps running the heater straight off battery to represent worst-case PWM.
 
A vendor of DC equipment put out a video of what happens when AC switches and breakers are used for DC. In his video, one just burned continuously. (I have my suspicion he designed his DC source to make this a good marketing video for his product.)

"thermal cutoff" - thing it'll actually cut anything off in your DC application?
"via PWM" - maybe that'll save the day. But does it every reach 100% on?

If you've salvaged any of these heaters, you could conduct a test where you overheat the cutoff and see if it actually does what you want, vs. just dissipating several hundred watts itself. Perhaps running the heater straight off battery to represent worst-case PWM.


As I tried to say previously, I am not using any AC thermal cutoff (if any ever even existed in this unit) or any of the AC switches or controls. I threw them away.

The heater is placed on a dirt floor in a greenhouse far enough away from any combustibles to not be an issue should it combust, in my estimation.

Since I am running 1000 watts through what was designed as a 1500 watt heater My assumption was that the heat dissipation design of the thermal fluid and radiator fins could handle it. I have been watching it closely and have noticed no indications of any overheating or thermal related issues. It has run at full throttle, 6-8 hours a day for about 3 weeks with no problems noted, other than a slow drip fluid leak at the heater element threads which I fixed with silicone high temp liquid gasket product from Permatex.

The heat output from the unit is very similar to when the unit was run on AC power at the medium setting, and thermostat on high.
 
It sounded like you were going to put them all around your greenhouse, that would require longer runs yeah?

No, will have 4 of them next to each other near the batteries. Building a rack for them... Don't want long lower voltage wire runs. The warm air should circulate from the heater location to the entire greenhouse just fine.
 
Don't want long lower voltage wire runs.

Yes that is best avoided.

I have a 12V 300W ceramic heater heating my bedroom, but I have an 80V solar run to a small 40A epever charge controller along with some capacitors. I will probably doument that soon, the smaller 20-40A epever charge controller don't require a battery to run, it will power itself off the solar and charge up the capacitors from 0V. Quite handy, and I have a longer higher voltage run rather than low voltage DC. (BTW, the larger 60-100A models require a battery to be present to power up).
 
Yes that is best avoided.

I have a 12V 300W ceramic heater heating my bedroom, but I have an 80V solar run to a small 40A epever charge controller along with some capacitors. I will probably doument that soon, the smaller 20-40A epever charge controller don't require a battery to run, it will power itself off the solar and charge up the capacitors from 0V. Quite handy, and I have a longer higher voltage run rather than low voltage DC. (BTW, the larger 60-100A models require a battery to be present to power up).

Would definitely like to see details of your build. Sounds interesting.
 
I'm just waiting on some capacitors from china to see if it works with different types, but they are taking their sweet time unfortunately.
 
While I do believe you can power up some CC with just capacitors, I don't believe you are getting efficient energy transfer at lower light levels. The math just doesn't make sense.
 
I converted an old oil filled radiator heater to be a dump load for our hydro/solar system. It dumps excess power as heat into our A=Frame greenhouse. I'm using the Midnite Classic 250 internal relay control along with a solid state relay to dump the excess power via PWM as the battery gets charged up. Got it working, still working on making it pretty...


Thanks for sharing! I've been immersing myself in this and other pv forums whilst looking at putting together an off-grid system. Veering towards a NIFE battery bank (enjoyed @bbobkins posts on the subject) - outline and discussion of my current musings are here - https://www.solarpaneltalk.com/foru...y/417683-dumping-pv-into-ptc-heating-elements

This seems a good way to go for dumping into heating elements and I know folk who favour Midnite charge controllers for NIFE banks.
 
While I do believe you can power up some CC with just capacitors, I don't believe you are getting efficient energy transfer at lower light levels. The math just doesn't make sense.

I think you have missed the point. The heater is being used as a dump to burn off extra energy, not actually intended to be used to heat the space durring "normal" operation.
 
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