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Author Topic: small off grid system design questions  (Read 2787 times)
mr_magicfingers
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« Reply #15 on: August 03, 2019, 12:01:43 PM »

Ok, getting somewhere a bit closer, thanks for all the help.

So, charge controller and bluetooth module are fine for this.
Ultimately, I need a different, bigger panel and different batteries and a more efficient inverter. That will be a little further down the line and can easily be changed out as funds allow, probably a bit at a time.

For now, I can series wire the two 80w panels easily enough to get the system running, I'll look at a larger panel next and may have found some used 255w panels for a budget price. I'm building a box to contain all the other bits and get them wired up safely.

So, next thing is correctly wiring the batteries. Thanks for the diagrams, I can see what I was doing wrong now. Just have to change the stack orientations and wire correctly. Will do that today and post some pictures before I connect it all to check I don't let the magic smoke out.

For a fuse between panels and batteries, how about a small circuit breaker like this one (of a suitable rating). It would act as an isolation switch and fuse/breaker in one neat unit.

https://www.ebay.co.uk/itm/30-Amp-Amplifier-Car-Audio-Marine-Boat-Circuit-Breaker-Trip-Fuse-Switch-12V-24V/133075828989?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D57477%26meid%3D8d6f836a7a2f431d923db681d8ebf0ce%26pid%3D100005%26rk%3D1%26rkt%3D12%26sd%3D171552429928%26itm%3D133075828989%26pg%3D2047675&_trksid=p2047675.c100005.m1851

Roger, thanks for the link to the clamp meter, I'll pick one of those up as I only have a regular multimeter. 

Batteries will need changing out for proper leisure batteries, that'll be next spring. The system is only in use from may to September, it runs the sand filter on a wood fired hot tub on our glamping site.

that leaves the inverter, any suggestions on a suitable model?

Thanks again.


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Solar PV: 6kw (24 x REC 250w), Sunny Boy 3600TL-21, roof facing 178 at 40 slope.
300l Thermal Store, 2 x 3kw immersions via Immersun + Dunsley Yorkshire WBS
Woodwarm Double sided 6kw WBS
7 acres of old woodland I'm slowly bringing back into order.
TT
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« Reply #16 on: August 03, 2019, 01:22:16 PM »

Keep the batteries away from the electronics too,
Stops the potential for gassing to ignite/corrode electronics.
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Tiff
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« Reply #17 on: August 03, 2019, 11:32:27 PM »

Ok, getting somewhere a bit closer, thanks for all the help.

So, charge controller and bluetooth module are fine for this.
Ultimately, I need a different, bigger panel and different batteries and a more efficient inverter. That will be a little further down the line and can easily be changed out as funds allow, probably a bit at a time.

For now, I can series wire the two 80w panels easily enough to get the system running, I'll look at a larger panel next and may have found some used 255w panels for a budget price. I'm building a box to contain all the other bits and get them wired up safely.

So, next thing is correctly wiring the batteries. Thanks for the diagrams, I can see what I was doing wrong now. Just have to change the stack orientations and wire correctly. Will do that today and post some pictures before I connect it all to check I don't let the magic smoke out.

For a fuse between panels and batteries, how about a small circuit breaker like this one (of a suitable rating). It would act as an isolation switch and fuse/breaker in one neat unit.

https://www.ebay.co.uk/itm/30-Amp-Amplifier-Car-Audio-Marine-Boat-Circuit-Breaker-Trip-Fuse-Switch-12V-24V/133075828989?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D57477%26meid%3D8d6f836a7a2f431d923db681d8ebf0ce%26pid%3D100005%26rk%3D1%26rkt%3D12%26sd%3D171552429928%26itm%3D133075828989%26pg%3D2047675&_trksid=p2047675.c100005.m1851

Roger, thanks for the link to the clamp meter, I'll pick one of those up as I only have a regular multimeter. 

Batteries will need changing out for proper leisure batteries, that'll be next spring. The system is only in use from may to September, it runs the sand filter on a wood fired hot tub on our glamping site.

that leaves the inverter, any suggestions on a suitable model?

Thanks again.




I've not tried those circuit breakers so can't comment other than I've never tried them because I dont like the look of them.

I prefer these (but they are still cheap chinese units) which appear to be clones of ABB units:

https://www.ebay.co.uk/itm/2P-Low-voltage-DC-250V-Miniature-Circuit-Breaker-for-Solar-Panels-Grid-System/352445551723?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


Note they are polarised breakers and you must understand how they work!!!!! The + and - do NOT denote polarity, they denote current flow.


Or keep it simple and use fuses. If you use automotive type blade fuses please pay a few pennys more and get littel fuses rather than cheap unbranded fuses.


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Robl
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« Reply #18 on: August 04, 2019, 10:18:55 AM »

Are you sure that you need an AC system ?  There are plenty of available 12V or 24V DC pumps - if you used one of these, then you could avoid the inverter and it's losses, so likely double overall pumping capability.  I think cheap DC pumps use DC motors, much more expensive (>200 ?) ones will have high speed AC motors with inbuilt drive electronics, which are significantly better than inverter + conventional AC motor. 
It's also safer to keep the voltage lower.
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mr_magicfingers
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« Reply #19 on: August 04, 2019, 12:21:49 PM »

Are you sure that you need an AC system ?  There are plenty of available 12V or 24V DC pumps - if you used one of these, then you could avoid the inverter and it's losses, so likely double overall pumping capability.  I think cheap DC pumps use DC motors, much more expensive (>200 ?) ones will have high speed AC motors with inbuilt drive electronics, which are significantly better than inverter + conventional AC motor. 
It's also safer to keep the voltage lower.

I ran a small 12v pump to start with but it didn't work very well and, because I need a filter, the 12v ones all use paper filters which need changing regularly and that gets expensive. This pump has a built in sand filter which is much cheaper to run. I'm starting to think it would be a lot cheaper to just dig a trench 100m and run an underground cable to the pump.
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Solar PV: 6kw (24 x REC 250w), Sunny Boy 3600TL-21, roof facing 178 at 40 slope.
300l Thermal Store, 2 x 3kw immersions via Immersun + Dunsley Yorkshire WBS
Woodwarm Double sided 6kw WBS
7 acres of old woodland I'm slowly bringing back into order.
Westie
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« Reply #20 on: August 04, 2019, 12:49:31 PM »

Are you sure that you need an AC system ?  There are plenty of available 12V or 24V DC pumps - if you used one of these, then you could avoid the inverter and it's losses, so likely double overall pumping capability.  I think cheap DC pumps use DC motors, much more expensive (>200 ?) ones will have high speed AC motors with inbuilt drive electronics, which are significantly better than inverter + conventional AC motor. 
It's also safer to keep the voltage lower.

I ran a small 12v pump to start with but it didn't work very well and, because I need a filter, the 12v ones all use paper filters which need changing regularly and that gets expensive. This pump has a built in sand filter which is much cheaper to run. I'm starting to think it would be a lot cheaper to just dig a trench 100m and run an underground cable to the pump.

Hmmm....  sounds like you suffer from one of my traits which is to get into the technical detail so deeply that you miss the alternative solution  banghead
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4kwp south facing array  SMA 4000TL grid connected.  2x30tube Navitron solar thermal panels (east/west). Arada 5kw S/C WBS. 25000Ltr underground rain water tank. KTM E-Bike  Cool
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