Experiment: electric immersion cup heater
I picked up one of of these immersion heaters from Amazon. I find myself needing to heat small amounts of water for tea, for bathing, etc. It’s part of the larger experiment to see how I might conserve cooking fuel. This one is 300w; I looked for a less powerful one (say 150-200w) but didn’t find one easily. They are cheap enough that if I find another one at the lower power rating I’ll pick it up and pass this one on to someone else.
One of the benefits of directly heating small amounts of water is that you are heating only the amount you need. When I do it in a teakettle I am often heating more than I need, thereby wasting fuel. I judge the amount of water in the kettle by weight. Next step will be to find (or replace) my thermometer so I don’t heat any more than necessary.
Cooking POV
I was heating up 2c of water in a widemouth mason jar with a coozie on it. The coil was making steam bubbles in their immediate area within a few seconds, and it took a minute or so for the water to get too hot to touch. I take from this that it’s overpowered for my needs (I have plenty of time!) and a less powerful heater would work fine.
I let it run a couple more minutes and before powering it down. It wasn’t boiling throughout the cup but it was seriously hot.
Power POV
We were in Float (~13.6v) when I plugged in the heater. It took about 30 seconds for the system to find equilibrium at max power, ~390w. It was about 4pm local, well past solar noon, or we might have seen ~500w. A more $$$ controller might have found Pmax faster – the BN-series Tracer is not known for fast acquisition of powerpoints. If I were doing it again I’d probably use the older A-series which is rather snappy and a bit cheaper. I have one of those in my DIY converter frankenstein setup.
Anyhow, back to the load. Flooded batteries are not known for their high throughput – system voltage sagged to 12.8v and stayed there during the heating. The shunt meter showed 500W+ being consumed, but that would be for the whole system. I was also running at least 40w of cryptomining, the van’s network, laptop, etc.
I think one reason it stabilized at 12.8v is that when it fell under 12.9v the opportunity circuit went offline, so kindle, phone and lithium pack charging, etc loads went away.
making the tea, system recovery
The tea steeped for four minutes; by the time I looked at the system again it had regained Vabs (~14.6 v) and acceptance had fallen way off to ~5A. A few more minutes and it only wanted 3.xA. The controller will try to hold Vabs for the 180mins I have configured it for, but the sun will start getting low soon. No worries; the batteries already have what they want.
Which remind me: I watered the batteries yesterday.