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I need to charge my glider batteries 2x7AH SLA from a larger 12 volt battery. Also would like to run say four 800 lumen lcd lights occasionally and from what I have read they should draw about 1 amp each and maybe a 12 volt soldering iron also occasionally which I think should draw about 4.5 amps. The 7 amp hour batteries would need to be charged overnight so that consecutive flying days would not cause any problems. The only option for power in the hangar is solar. I am thinking of getting a 100w panel connected to a 60 Amp Hour battery through a 20 amp PWM solar controller. I do not know much about solar or electronics in general but from what I have read I am thinking it should be possible to connect a buck/boost converter to the load terminal of the PWM controller to step the voltage up to whatever is required to charge the small batteries and then connect the output of the buck/boost to the input side of a second PWM charge controller to take care of regulating the charge so the small batteries are not overcharged. The setup downstream of the large house battery would only cost in the order of $100 or so and is the main reason for my thinking. I have seen commercial dc to dc chargers for sale which would do the job but they are several hundred dollars. Is this a case of you get what you pay for or is my system a workable solution? Any alternative suggestions or opinions on this are most welcome.Thanks in advance.
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you can't charge a 12v battery, from a 12v battery. Lead acid batteries need about 14v or so, to be charged from, you need the couple extra volts to force the charge into the battery.
the simple thing, is to pull the batteries out, and charge them at home
Next simple thing is to mount a " milk crate" to a hand truck, and put a 90ah deep cycle battery in it, wheel it back and forth, and use a small 120V inverter to power the charger for the 2, 7ah batteries overnight.
Adding about 200W of solar to the hand truck would be the next step up.
But you can't just hook 2 batteries together and have one charge the other. The "chargee" will never get a full charge from the donor battery, you need the inverter to power the proper charger for the glider batteries. The other gear, you run off the large 90ah deep cycle battery.
Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister -
This page might contain multiple chargers that wouldn't need an intermediate inverter/charger combo.
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Thanks for the response Mike but I don't think you are correct in your assumption that you can't charge a 12 volt battery from another larger 12v battery. That is the purpose of the buck/boost converter in the setup. It boosts the 12v up to whatever voltage you want within the limits of the device albeit at the cost of increased current draw. Which should not be a problem in this case given the size difference in the two batteries.The thing I am unsure about is hooking two charge controllers up in the manner suggested in my original post. I was hoping someone on here had done something similar. Charging at home is not an option as the glider is owned by a syndicate of three and we all need access to the batteries.Comment
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Thanks AZ. These are the DC to DC chargers I mentioned in my original post but there is one in there (PST-PB1108) that is not all that expensive. $200 Australian delivered and it might do the job. It says it is constant current constant voltage so I am unsure if leaving the 7 amp hour batteries connected to this unit for days and sometimes a week or two would harm them or whether it has an inbuilt charging algorithm that would protect the battery being charged. Anyway thanks again for taking the trouble and I will ask the distributor if it will work for my application.Comment
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I don't think I understand the purpose of the second PWM controller. If I did, I would have addressed it along with the 12 volt chargers.Comment
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I think the idea is that PWM1 charges the 60 Ah battery, using PV as the source. PWM2 charges the 7 Ah batteries, using a boost circuit as the source, which is fed by the 60 Ah battery. I'm not sure what the PWM really offers here, except I guess some ability to reduce the boosted voltage back down to a float voltage for long term maintenance. It seems like a boost charger with adjustable output would eliminate the need for PWM2.
The PST-PB1108 only boosts to 13.8 V, and I'm not sure what the 7 Ah battery will want as the charge voltage.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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Then perhaps the PST-BC1212-15 from that same page. Adjustable current limit and floats after absorb. No second PWM controller. If not, I'm sure the right one exists. Usually finding the first few can open up the flood gates to many similar models.Comment
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Sensij is correct.The second charge controller was intended to protect the 7AH battery and provide the correct charging cycle and float when it is left unattended for a week or two. Yes AZ the 1212-15 would work for sure but its nearly $300 Australian.Ideally I would love to find a boost converter that has a charging algorithm for SLA all in one component but I don't know if such a thing exists. I suspect that is what the $300 chargers that AZ pointed to are.My setup if it will work would be only $40 or so but I do not know if it will actually work.Comment
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Raypat ,
Yes, you can charge your 7 AH 12 volt batteries from a 60 AH 12 volt battery.
All you need is something like this ...
https://www.amazon.com/OptiMATE-TM-5.../dp/B011J76CFE
I am not recommending that particular model.
If you do not understand the PV Solar Panel stuff,
then just buy a kit containing the 200 Watt Solar Panel & 12 Volt Charge Controller.
Like this ...
https://www.ebay.com/itm/160-Watt-Of...kAAOSwHsRYCDGF
Buy the 60AH Deep Cycle battery from Walmart
$80 = Marine Deep Cycle Group 24DC
$90 = Marine Deep Cycle Group 27DCLast edited by NEOH; 11-09-2017, 10:04 AM.Comment
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They're making 175 and 180 watt 12 volt panels as well.
https://www.ebay.com/itm/1-175-Watt-...YAAOSw-29ZXumz
Last edited by littleharbor; 11-09-2017, 10:34 AM.2.2kw Suntech mono, Classic 200, NEW Trace SW4024Comment
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I see that. I guess I am a little confused since the number and size of the 36 cells is not more than say a 100 watt panel.
I am not sure how they are getting a higher Vmp or Imp to generate more wattage without using bigger cells.
I guess they have found a way to increase the efficiency of a 5" cell compared to the ones found on earlier version panels.Comment
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These are 6" cells in a 4 x 9 arrangement. Typical 26" x 56" Approx. . Voltages are up a little but they are getting higher amperage from these more efficient cells. The Typical 100 watt panels are using 4" x 6" cells these days.
It does seem strange seeing 36 cell panels putting out more power than the 72 cell panels from not so long ago. There's still a viable market for 12 volt panels from my experience and these higher output modules are certainly welcomed.2.2kw Suntech mono, Classic 200, NEW Trace SW4024Comment
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I see that some of those higher wattage panels are 26" x 56" but some are still 22" x 48" which is the size of that 160watt one that NEOH posted and is pretty standard for 80 to 120 watt 12v panels using 5" cells. I have 6 panels in the 80w - 90 watt range which were purchase about 5 years ago.
Again the older cells are probably just less efficient so the output is limited to less amps then the newer versions.
Also it is nice to see the 36 cell panels have come way down in price per watt.Comment
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