Robert Ray

I'll try and pull up a picture today, I have seen a WWII immersion water heater that would be placed in a 55 gallon barrel. The base and burn chamber a donut shape that rested on the bottom of the drum and the chimney and feed stack up to the top of the barrel. At the top a vessel of a couple of gallon vessel held diesel or waste oil that  drips oil down the chimney to the burn chamber. No reason the heating medium couldn't be sand.

This popped up today:
https://www.facebook.com/reel/1297530505754768

reminds me of my pitch bowl.

I don't have a RMH, but I do want to try a sand battery heater in the green house.
My test will be creating a sand battery 2ft x 2ft x 12 ft corrugated sides, to simulate the mass of a RMH Two courses of bricks at the base, the remainder will be filled with sand.
I picked up the bed materials today from Home Depot. Spent some time with Jeff Besos ordering heating elements from Amazon today.
My experiment will be placing the different elements within the central 4 feet of the bed.
The heating elements I ordered consist of a broiler element, a water heating element, an industrial immersion heater, a clothes dryer heating element, an eight inch stove top element, 6 PTC elements. So about 150.00 dollars worth of different heat sources that will be placed within that central 4 feet of the 12 ft bed.
I will be using an EL-USB-1-PRO temperature logger set to read at 15 min increments.  I will use three candy thermometers  pushed into the sand to monitor visually. I have a laser thermometer to check side temps from top to bottom. I only have one day off a week. That one day I will run un-switched to see how hot it will get. 130-140 seems to be the upper limit of a comfortable heated seat so that will be my temp setting when running through the switch.
I will try two different switch types, a water heater switch and a stove bourbon tube style. I will run direct from the solar panel to each element, switching to a different element after a seven day run.
Should I create a void down the center to simulate the RMH chimney?
If nothing else I hope to use the sand battery as a heated seed starting table during my trial run.
Any suggested additions to the experiment?
I do have a 500 watt wind turbine that I considered hooking up to wring some energy out at night but think I'll hold off for the initial trials.

William,
AC resistance heaters will heat up with DC voltage. A water heater switch affixed to the mass of the RMH in a similar fashion to how they are affixed to the water tank, the back temp sensing portion pressed against the mass wouldn't care if it were AC or DC either. Sensing temperature on the bench portion of the RMH and shutting it down at a safe temp..
We wouldn't be within the bell we would be imbedded within the mass part of a RMH.
We could loop into a solar array that is dumping after the battery bank is full, or be using a direct lone panel or two
Moisture concerns within the RMH shouldn't be an issue after the heater has run a few cycles and cured.
Imbedded in the mass the element through conduction heating the mass allowing the mass to radiate after it is charged.

Benjamin, the heat transfer of a resistance heater in the battery mass would be through conduction, no need for the addition of a fan.

Benjamin, we have the RMH mass. what is the difference in charging that mass with fire and a heating element. The addition of a free stacking method to heat that mass that requires no labor input or fuel after install. Let's forget sand battery since that seems to be an issue and call it thermal mass. A RMH's mass is a proven heating system the hiccup seems to be how we are charging the mass. The Polar Night system I reference was to show that a sand battery is in use, but it is using an entirely different process to use that heat. Charging the RMH mass is an elementary process.

I imagine it would depend on the construction of the RMH. An oven element placed between a course of bricks would cover the most area and are usually over 3000 watts. PTC's are a low draw and quite small. Commercial immersion heaters vary in length and diameter; water heater elements are the same. The greater the area of contact would be ideal, but the immersion heater or water heater element would still heat the mass.
We can surmise that a water heater element can heat 50 gallons of water to over 100 degrees and it takes more energy and time to initially heat 50 gallons of water than 50 gallons of sand. Let's assume that the mass of a RMH is in that 50 gallon size.
If one is running off of an established solar charging system and are just dumping excess from when that battery bank is full, we'd have a figure that we could draw from. If we are just running off of a single solar panel it might be a bit harder to get a number to plug in a formula.

R. Scott exactly. If your already running solar the RMH heating element would be a place to dump excess charge. If you're not on solar a single panel would be able to heat the element when not on site. A thermal switch would isolate the element when not needed.

One would have a storage vessel in the mass of the RMH. A redundant way to heat that mass that requires no physical presence or labor with a small financial cost. It would be off grid. It would not interfere with the operation of the RMH. Stacking functions, an additional method of heating the thermal mass. I am just looking at storing the heat not using the heat to produce anything other than charging the thermal mass for heat.