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Comment by mikestew | Hacker News Reader

I figured this to be some rinky-dink setup with some teensy pocket solar panel. I mean, $200? Hell, a decent 100W panel will cost you that much.

100W panels are $94 now? Holy crap, if we used more power boondocking I’d cover the roof of the camper with them. But we don’t use the power we make now, with a propane-powered refrigerator and LED lighting. And that’s the problem with solar, it can power the little stuff, like LED lights or a small invertor, and 100W panels are almost overkill. But get to something like a fridge or A/C for even a small camper, and one will need multiple panels and a big set of batteries.

Nice setup, and I wish them well with their turnkey solution.

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Solar panels are incredibly cheap, now. If you buy them by the dozen, you can get them for just 49 cents per Watt nowadays from places like renvu.com (no affiliation).

Spot market for PV modules is as low as 28 cents per Watt. Just the cells are as low as 20 cents per Watt. pvinsights.com (These are before tariffs, I think.)

We're in a very different world from when dollar-a-watt (at the cell level) seemed like the holy grail.

They mention a swamp cooler in the article, which is surprising. I would expect those to have a big power hungry fan motor that's too much for the panel.

They do say it's a DC based swamp cooler. Looks home made though...more detail on it would be interesting.

After a relatively blistering summer here in Seattle, here’s something I’ve considered building for when we leave dogs in the camper: http://www.mdpub.com/swampcooler/index.html. Eight watts for the fans, and the bird bath pump can’t be but a couple of watts. Easily done with a 100W panel, should be able to run overnight with a reasonable battery. That’s going to cool a room or a camper, though, and not a house.

That's helpful, thanks. I usually picture a squirrel cage fan with a big AC motor that has a big current draw at startup when I hear "swamp cooler".

I was under the impression swamp coolers needed big air flow to work well. Seems maybe not?

Isn't the humidity in the PNW way too high for swamp coolers to work?

Yes

High? I keep an accurate and calibrated hygrometer in the musical instrument room, and it's the rare day when it goes over 50% in Redmond. That said, I've never used one in the PNW.

According to the chart at the bottom of this article, it's not optimal, but it'll take the edge off: https://www.air-n-water.com/common-swamp-mistakes.htm. And for most summers, this one being an exception, our problems with heat are in the high desert east of the mountains.

Be careful and make sure you have redundancy, temps in campers can go way way up with a malfunction of the fan.

A solid point. Our mitigation is that it's a pop-up VW with a canvas tent and screen windows, and curtains on the glass windows. Even in the 90s parked in direct sun it'll stay cool enough to take a nap. It'll be a sweaty nap, but no one's going to die. And the design I linked to has four fans.

But now you've got me thinking about some WiFi or LTE module that monitors continuity or voltage, build a companion phone app that gets pinged when $SOMETHING goes wrong. :-) (Our use case is bluegrass festival->leave dogs in camper to see show, so we're never very far away.)

I would measure temperature directly, rather than continuity or voltage. It's what you really care about.

There exist smartphones with ambient temperature sensors; if you already have USB power, this is only a few hours of hacking.

I would measure temperature directly, rather than continuity or voltage. It's what you really care about.

Duh, of course. That's why they don't let me design things. :-) (Though in my defense, it was an "off the top of my head in 500ms" thought.) Plenty of power available, the only issue would be connectivity, as there's about a 50% chance that any festival we go to won't have a cell signal. Which makes me wonder how hard it would be to rig something that sends an APRS message over amateur radio frequencies when a the alarm has voltage, or something.

Anyhoo, this is drifting way off topic. If I get around to making something, I'll post a Show HN.

    big power hungry fan motor

Fans don't use much power. 50W would be fine for a swamp cooler for a tent. Are you thinking of on air conditioning compressor?

Here is a relatively tiny swamp cooler. It consumes 65 watts: https://thelashop.com/products/65w-portable-evaporative-air-...

I would have concerns with a 100 watt DC panel being able to handle a 65 watts AC swamp cooler. Conversion loss, motor startup current draw, etc.

Big alternating current fans that can move air do use lots of power. Especially a current surge at startup.

It sounds like in this space, people are making their own direct DC powered swamp coolers that are using less power, with relatively low flow fans. That's what I was missing.

> They do say it's a DC based swamp cooler. Looks home made though...more detail on it would be interesting.

Called something like a "Burning Man Bucket Swamp Cooler":

https://eplaya.burningman.org/viewtopic.php?t=33842

Simple and cheap to make; the problem with swamp coolers at Burning Man is the dust. Eventually the water turns to mud, and the pads get caked in it. Plus, you have to carry enough water not just for drinking, but to run the cooler too.

But that's at Burning Man - in other contexts it works as well as any other similar cooler.

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