radmon.org Solar Power experiments

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2 years 7 months ago #4941 by mw0uzo
Here's a picture of the solar setup and the RPi4 server

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2 years 7 months ago - 2 years 7 months ago #4943 by mw0uzo
It's not the tidiest of setups, but it is experimental and the first one I've put together.

There is 140Ah of lead acid batteries, taken from cars. Batteries that have just started to go bad and turn over the engine poorly in winter, apparently have years of life left when recovered with controlled overcharging at 15.5V and used in lower current solar service.
Last edit: 2 years 7 months ago by mw0uzo.
The following user(s) said Thank You: GetSirius

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2 years 7 months ago #4945 by jnissen
Absolutely fantastic! I love the updates and the site is actually responsive. All this and only on a little Raspberry Pi? Very cool for sure.

Hopefully your batteries last. I have not had good luck with old car batteries even for light loads.

Is this a completely off grid setup or do you feed into the grid? I see an inverter on the wall? I have a shed with solar and an inverter to run lights, motion sense lights at night, etc... My inverter idle current was critical to making the system work for me. Eventually settled on a small inverter with very good idle currents. No fan on light loads so the battery remains charged even on extended cloudy days in winter.

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2 years 7 months ago #4946 by FSM19
Most impressive, but way beyond me!

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2 years 7 months ago - 2 years 7 months ago #4950 by mw0uzo

Absolutely fantastic! I love the updates and the site is actually responsive. All this and only on a little Raspberry Pi? Very cool for sure.

Hopefully your batteries last. I have not had good luck with old car batteries even for light loads.

Is this a completely off grid setup or do you feed into the grid? I see an inverter on the wall? I have a shed with solar and an inverter to run lights, motion sense lights at night, etc... My inverter idle current was critical to making the system work for me. Eventually settled on a small inverter with very good idle currents. No fan on light loads so the battery remains charged even on extended cloudy days in winter.


I was wondering how well it was working out in the field. It seems pretty good here, instant load up with occasional lag for some reason, which I believe might be data writes stacking up into a big chunk every now and then. Even mouse/UI freezes briefly when this happens, so it's hardware/lowlevel software issue. To take it easier on the SD card I am planning on moving logs and the database onto real spinning media. But, there is always a downside. The stack of USB3->SATA adapter, fixed 12V additional supply(11V-16V not good enough) and HD hanging off the adaptor makes for something physically and electrically more vulnerable than an SD card in the Pi. I think I will take another backup image when I finish the last round of improvements and use HD for backup and see how it goes. If the card makes it through a year of 'production' service I will forget about it.

The batteries were not happy when I first got them. The small 20Ah AGM one would not take a charge, but had a healthy 12v across it. I removed the caps and the insides were bone dry not a trace of moisture on the glass mat. So I just put some deionised water in with a syringe in each cell until the water just reached the top of the plates. Then 15.5V with a current limit of 300mA was applied for at least a week. This desulphated enough so some current could be drawn and after 4 or 5 cycles with 24hr desulphating charges inbetween the capacity was up to about 10Ah. Having been in the solar rig for two months it has improved further and I can now run my HF radio of it drawing 10A+ intermittently and 2.5A constantly for hours. I haven't done a proper capacity test yet, but with the improved performance I wouldn't be surprised if it was 15Ah.

The 40Ah mid sized battery is from our car, the CCA isn't enough to turn over reliably in cold weather. I believe it is 10 years old. It was standing for a few years with occasional top up charge, used for power when camping. I put it on the usual desulphating charge for a while, and it easily delivers 30-40A. Estimated capacity 30Ah? This was the main battery for a few months in the solar rig.

The 80Ah battery is a diesel starter, no maintenance. I had to drill holes in the top to view condition inside. Plates looked sulphated, so desulphated for 3 or 4 days. Then wired it in. Not sure of capacity, but I suspect it's pretty good. Internal condition, apart from sulphation looked nice and the electrolyte was full.

It is an off grid setup. I too had problems with inverter idle current. A 600W Maplin one I had drew way too much idle current 800mA+? and was unreliable powering things. The 300W one in the picture has about 350-400mA idle. I never run it really, as all solar powered equipment connected is for 12V. And the total efficiency for anything run through the inverter is rubbish probably 50%. The PC that radmon.org ran on for a few weeks scoffed 60W and that easily translated to 100W+ into the inverter.

It is surprising though how much battery you need for even supplying 10W constantly. A week of yucky cloud in winter can leave battery voltage pretty low. Most of the time, however, batts are full by about 11am.

Incidentally, with Gel type batteries, they can also be flooded with water up to the top of the plates for recovery, they do dry out too. And if there is excess water in there, treat it like a flooded cell. Excess electrolyte is is must for desulphating at 15.5V.
Last edit: 2 years 7 months ago by mw0uzo.

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2 years 7 months ago - 2 years 7 months ago #4951 by mw0uzo
I also have one of those CLEN pulsing desulphator things. I never got any real measurable results from that on the bad batteries used in the rig. However, if the battery is brought up to 15.5V AND the desulphator is used, there appears to be a real effect from the pulsing. During and for a short period after the pulsing, battery voltage *falls*, indicating that some lead may well be moving from an inactive state to an active state. It isn't the pulser interfering with the power supply I use either, as no battery gives no effect. And it's not the current limit as that was increased to test. So something IS happening during the pulses at 15.5V. If the voltage is lowered back down to say 14V, nothing happens. I suspect that the plates being brought up to a voltage where desulphation actually happens anyway AND the pulses on top might actually be working.

I'm not a battery expert though, so take my musings with a pinch of salt :lol:
Last edit: 2 years 7 months ago by mw0uzo.

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Solar powered Raspberry Pi 4 server stats: CPU 60% Memory 18% Swap 20% CPU temp=81.3'C Uptime 63 Days