Interesting solar issues

[Zephod]

I have a 2.5A marine bilge fan as my extraction fan at the back of the bus.

Powering that I have two 10A solar panels feeding into a Chinese CMTD charge controller with the trigger voltage set to 13v and the power off voltage set to 11.9v

I have several batteries - a 10AH SLA and two 7AH SLA. I was running with the 10AH SLA but now I'm running with the two 7AH in parallel.

The problem I'm getting is reducing fan run time. The voltage climbs rapidly to full voltage then the fan runs for about 10 seconds before stopping as the switch off voltage is reached.

Initially with the 10AH battery I was getting 10 minutes of run time. Now I'm pretty sure than 50% of a 10AH battery should provide 5AH of power or approximately two hours of running a 2.5A fan. Even assuming some massive starting current I should be getting way more than 10 minutes.

Anyway, that 10AH battery now won't charge beyond 12.5v so I switched to the 7AH batteries in parallel.

I started the system today after a few days inactivity and the batteries took a long time to charge up, reached 13v and the fan ran for 2 minutes. Subsequent run times were in the region of 10 to 20 seconds.

The 7ah batteries were bought at the same time, from Radio Shack (They're marked Radio Shack) in their going out of business sale.

I'm not sure quite what's going on. I know the charge controller reports the temperature in its vicinity as 40C which would be 104F quite often - which would be about right for the internal temperature of my bus.

Out of interest with the batteries unplugged, the resistance measured across the battery connectors on the charge controller was about 250K.

Previously I used that same controller with a pair of CPU fans and a 5AH battery. The fans would run and run.

I'm wondering whether the controller (which is about a year old) has gone bad to the point it's wrecking batteries. Has anybody heard of such a thing?

Meanwhile I ordered a fresh charge controller that's simpler. This one just has LEDs and nothing to set. It's set for lead-acid batteries. I'm pretty sure it'll turn out to be Chinese like just about everything else one buys these days. I do have other charge controllers (also from China) but they're unusable due to their switch off voltage having a maximum of 11.3V which would wreck even deep cycle lead-acid batteries.

I doubt it's a problem with the cable as the cable under the bus is bundled in a cable wrapper with other cables, none of which have shown any problems. I know the cable core is not touching bodywork or other cable cores.


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[Jeremy]

I notice you say "I have two 10A solar panels" - solar panels aren't sized in amps, they're sized in watts - assuming you have two 10w panels that will give you, assuming full sun and panels angled properly (ie. not mounted vertically!) not much more than 1.5 amps at 12v

Jeremy

[Zephod]

I notice you say "I have two 10A solar panels" - solar panels aren't sized in amps, they're sized in watts - assuming you have two 10w panels that will give you, assuming full sun and panels angled properly (ie. not mounted vertically!) not much more than 1.5 amps at 12v

Jeremy

Correct, two 10W panels. If it takes 30 minutes to charge the battery and 10 minutes fan usage, I've already changed all the air in the cabin. That fan pumps 130cfm and 10 mins should clear the bus.


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[jcdillin]

I've had terrible luck with the cheapie Chinese charge controllers, they love to destroy SLA batteries. Between overcharging and over-discharging I've had them destroy batteries in just a month.

The only unit that so far has been consistent and keeps the batteries healthy is this one.

http://amzn.to/2voYhMO