Vigilant24
New Member
- Joined
- Aug 23, 2022
- Messages
- 119
Hello, I've enjoyed reading about the many projects here and finally joined up to dip my toe in. nThanks in advance for any assistance. I'm designing a small (cheap) solar backup system primarily to have emergency power if our grid goes down (regional ice storm or worse). It's just for the very, very basics (well water, light, tools, a fan, etc)
The total electrical loads would be modest, I'm figuring about:
- 20 minutes of submerged well pump use per day (115VAC, 1/2 HP. load: 900 watts when running BUT starting load of about 6000 watts)=300 Wh
- Recharge tools, fan, flashlights, radios, etc: = 400 Wh
So, about 700 Wh per day. No refrigerators, AC, etc. Some of that won't need to go into battery storage (e.g I can recharge all the tools, flashlights, fan during the day)
- The system I have in mind:
- Panels:
2 x 100W panels, I plan to run them in parallel, for a "12V" (nominal) system. So, in theory, up to 1000 wh of collection in perfect conditions.
- Storage: Right now I intend to use a single 12V marine "deep cycle" battery of 105 AH capacity (= 630 WH if discharged to 50%). It's not ideal, but it is inexpensive, available, sturdy (no BMS electronics to crump out), and if need be I can lug it to a car for an emergency recharging from the car alternator in a pinch.
- Charge controller: TBD. I own a 10A Renogy Wanderer PWM controller now.
- Inverter: TBD. I'll get a true sine wave model. If I must accomodate the 50 amp (120VAC) starting load of my well pump I might be able to get by with a 3000 watt (6000 wat surge) high frquency inverter. If I can use a soft-start device to bring down that starting surge I could use a much smaller (and less expensive) inverter.
Observation: That starting load of the well pump is the killer.
Some of my newby questions:
1) Charge Controller: Will a PWM controller provide DC voltage at something close enough to 12VDC to allow me to run an inverter off the battery charging leads? I know this sounds basic, but some descriptions I read indicate a PWM controller merely supplies the battery with the same voltage it gets from the panels, turning it on and off rapidly so the wattage going into the battery is the right amount for the battery's particular state of charge. Is that right? Would a MPPT charge controller provide voltage more suitable for running an inverter in the daytime?
So, I'm wondering if should I get a 20A PWM controller? Spend more for a 20A MPPT controller?
2) While my fully charged battery might have a useable capacity (to 50% discharge) of 630 Wh, if I power that 800 watt well pump with it for 20 minutes, the discharge rate/Peukert equation indicate I'll probably be lucky to get the 300WH I need for 20 minutes of pumping for one day. Buying another 105 AH battery might be a good idea, lowering the discharge rate of each one and providing at least one day of pumping if we get zero solar input.
3) Dealing with the pump starting surge. Any ideas on how best to do this? My well pump is a two wire 115 VAC 1/2 HP. I'm not too excited about the idea of paying thousands of dollars for a (very nice) Grundfoss DC pump. It appears that a Schneider Electric soft start device (their model number 6VMD4, cost $183) might work with my existing pump, and would let me go with a much smaller inverter. I've even considered the idea of snaking a small 12v sampling pump into my well beside my existing well line, power wires, etc. Something like this "Tornado" sampling pump (about $340) could give 1 GPM from a depth of 70 feet. Claimed motor life of about 400 hours, so that would be good for a few months of use (3 hour per day). It draws up to 210 watts, but if I've got good sun then that's not much more than the panels are producing, so little draw from the battery and no load on the AC inverter at all. If I wanted pressurized water in the house, I'd need to separate pump to do that, but an inexpensive 12V RV pulse pump could do that.
4) If I just use my existing 115VAC pump with no soft-start, the starting surge load will be about 50A (6000W). The marine battery has a claimed 500 Cold Cranking Amp capacity = 6000 watts. After inverter losses, probably not enough. Can I safely run that 12V battery in parallel with a regular automobile 12V starting battery >just for the starting period< of the motor? I know it;s generally not a good idea to attach batteries of different constructions or capacities in parallel, but I'd just do this to cover the motor starting load, then disconnect the car starting battery and charge it separately later. So, there shouldn't be much swapping of electrons between the batteries, unbalanced charging, etc.
Anyway, that's the outline of my little project. Any thoughts, harpoons, suggestions are welcome.
Mark W
Dayton, OH
The total electrical loads would be modest, I'm figuring about:
- 20 minutes of submerged well pump use per day (115VAC, 1/2 HP. load: 900 watts when running BUT starting load of about 6000 watts)=300 Wh
- Recharge tools, fan, flashlights, radios, etc: = 400 Wh
So, about 700 Wh per day. No refrigerators, AC, etc. Some of that won't need to go into battery storage (e.g I can recharge all the tools, flashlights, fan during the day)
- The system I have in mind:
- Panels:
2 x 100W panels, I plan to run them in parallel, for a "12V" (nominal) system. So, in theory, up to 1000 wh of collection in perfect conditions.
- Storage: Right now I intend to use a single 12V marine "deep cycle" battery of 105 AH capacity (= 630 WH if discharged to 50%). It's not ideal, but it is inexpensive, available, sturdy (no BMS electronics to crump out), and if need be I can lug it to a car for an emergency recharging from the car alternator in a pinch.
- Charge controller: TBD. I own a 10A Renogy Wanderer PWM controller now.
- Inverter: TBD. I'll get a true sine wave model. If I must accomodate the 50 amp (120VAC) starting load of my well pump I might be able to get by with a 3000 watt (6000 wat surge) high frquency inverter. If I can use a soft-start device to bring down that starting surge I could use a much smaller (and less expensive) inverter.
Observation: That starting load of the well pump is the killer.
Some of my newby questions:
1) Charge Controller: Will a PWM controller provide DC voltage at something close enough to 12VDC to allow me to run an inverter off the battery charging leads? I know this sounds basic, but some descriptions I read indicate a PWM controller merely supplies the battery with the same voltage it gets from the panels, turning it on and off rapidly so the wattage going into the battery is the right amount for the battery's particular state of charge. Is that right? Would a MPPT charge controller provide voltage more suitable for running an inverter in the daytime?
So, I'm wondering if should I get a 20A PWM controller? Spend more for a 20A MPPT controller?
2) While my fully charged battery might have a useable capacity (to 50% discharge) of 630 Wh, if I power that 800 watt well pump with it for 20 minutes, the discharge rate/Peukert equation indicate I'll probably be lucky to get the 300WH I need for 20 minutes of pumping for one day. Buying another 105 AH battery might be a good idea, lowering the discharge rate of each one and providing at least one day of pumping if we get zero solar input.
3) Dealing with the pump starting surge. Any ideas on how best to do this? My well pump is a two wire 115 VAC 1/2 HP. I'm not too excited about the idea of paying thousands of dollars for a (very nice) Grundfoss DC pump. It appears that a Schneider Electric soft start device (their model number 6VMD4, cost $183) might work with my existing pump, and would let me go with a much smaller inverter. I've even considered the idea of snaking a small 12v sampling pump into my well beside my existing well line, power wires, etc. Something like this "Tornado" sampling pump (about $340) could give 1 GPM from a depth of 70 feet. Claimed motor life of about 400 hours, so that would be good for a few months of use (3 hour per day). It draws up to 210 watts, but if I've got good sun then that's not much more than the panels are producing, so little draw from the battery and no load on the AC inverter at all. If I wanted pressurized water in the house, I'd need to separate pump to do that, but an inexpensive 12V RV pulse pump could do that.
4) If I just use my existing 115VAC pump with no soft-start, the starting surge load will be about 50A (6000W). The marine battery has a claimed 500 Cold Cranking Amp capacity = 6000 watts. After inverter losses, probably not enough. Can I safely run that 12V battery in parallel with a regular automobile 12V starting battery >just for the starting period< of the motor? I know it;s generally not a good idea to attach batteries of different constructions or capacities in parallel, but I'd just do this to cover the motor starting load, then disconnect the car starting battery and charge it separately later. So, there shouldn't be much swapping of electrons between the batteries, unbalanced charging, etc.
Anyway, that's the outline of my little project. Any thoughts, harpoons, suggestions are welcome.
Mark W
Dayton, OH
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