Solar 12v 40amps ??? - Page 1
Forum section: electronics / general

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 29, 2014, 03:47:30 pm
content: I wanna run a device using solar energy, the device users 12v at 40amps.Is it best to run it strait off the battery bank or use a inverter to bump it up to mains ac then use a power supply to drop the voltageback down to 12v dc.

author: Tinkerer
author_rank: Frequent Contributor
timestamp: August 29, 2014, 04:20:34 pm
content: Solar is already in DC, there is no benefit to be gained from converting it to AC and back here. It would be best if you were to use the cells to charge a battery and the battery to run the device. You will need a charge controller though.At 480W, thats a large area in solar cells, taking an educated guess, I would say possibly something like around 1sqm would be needed.(note, thats just a good guess and size will vary according to location, efficiancy, etc)

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 29, 2014, 04:32:28 pm
content: The device is in the shed and the solar panel will be on the roof. 1 sq meter you think. would a 100 watt panel do it?

author: Tinkerer
author_rank: Frequent Contributor
timestamp: August 29, 2014, 09:28:00 pm
content: Quote from: snipersquad100 on August 29, 2014, 04:32:28 pm12V at 40A is 480W. I assume this device wont be running all the time? You will want a solar panel that can keep the batteries charged enough and that will require you to figure out how much time the device will be running and the amount of sun you typically get and all that.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 29, 2014, 10:42:30 pm
content: its an antminer so needs to stay on as much as possible, if its possible.Maybe a mix of mains and solar?

author: Tinkerer
author_rank: Frequent Contributor
timestamp: August 29, 2014, 11:17:00 pm
content: Quote from: snipersquad100 on August 29, 2014, 10:42:30 pmOk, well obviously the sun isnt shining 24/7, so yes, you need either alot of batteries or mains or a mix of both.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 31, 2014, 02:43:06 am
content: Is it possible to have a system that switches to mains power when the battery bank level drops to a certain voltage say 11.2v without it interrupting the power to the antminer?

author: amyk
author_rank: Super Contributor
timestamp: August 31, 2014, 03:48:15 am
content: 480W is a huge amount of power for a solar panel... and all bets are off if you live in an area that doesn't have sunny weather most of the time.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 31, 2014, 04:30:38 am
content: Quote from: snipersquad100 on August 31, 2014, 02:43:06 amJust connect a power supply in parallel with the battery and set it for the desired voltage. It won't actually supply power until the voltage drops low enough.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: August 31, 2014, 01:54:35 pm
content: I've just picked up 5 110ah leisure batteries and ordered a 180watt solar panel, a 500watt wind turbine and a Corsair PSU 750W ATX Power Supply in case the voltage drops on the battery bank. surely that would be enough to keep the device going.I need a bit more advice on connecting the psu to kick in when batteries go low.thanks

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 01, 2014, 02:14:04 am
content: Easiest is to use a big Schottky diode so the PSU can supply the batteries but not backfeed. Then add a comparator (noise filtered!) to enable the PSU below about 11.5V and disable it above 12.6V. For better efficiency, use a MOSFET instead of a diode, although that will require more elaborate controls.

author: tszaboo
author_rank: Super Contributor
timestamp: September 01, 2014, 06:42:31 am
content: Quote from: NiHaoMike on September 01, 2014, 02:14:04 amAt 40A most power Schottky drops above 1V, so you have to dissipate 40W. I would use one of those ideal diode or powerpath controllers. But putting a solar panel in England in autumn and expecting results is just not going to work.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 01, 2014, 03:52:42 pm
content: Thanks for the help guys.Im looking more into wind power, one thing im not short of here is wind lol

author: mtdoc
author_rank: Super Contributor
timestamp: September 03, 2014, 03:41:47 am
content: Quote from: snipersquad100 on August 29, 2014, 04:32:28 pmNot even close. To know how much solar (wind, or any intermittent RE source) you need it's best to define your total 24 hour load.480 watts if continued for 24 hours = 11.5 kWh per day. That is a large load - enough to power a large home sans heating and cooling.Whether using solar or wind you will need a battery bank since these are intermittent sources of energy. If using traditional lead acid batteries you generally want to plan on 2 days of autonomy in case the sun doesn't shine or the wind doesn't blow. You also never want to discharge your deep cycle lead acid batteries below 50% SOC. So that means a battery bank with the capacity to store 4X your total dally load!In the example given this would mean a 46 kWh battery bank!If using solar you can expect the total energy available for loads to be 75-80% of the nameplate, STC rating. Losses due to temperature, wire losses, charge/discharge inefficiencies add up so that you will rarely if ever see a peak output as high as the nameplate rating.How much PV energy you harvest in 24 hours depends on the solar insolation of your location along with associated seasonal variations. Typical is to plan for 4-5 hours pf peak sun. So - when all is said and done - for most locations the size fo a PV array will need to be about 1/4th of your anticipated 24 hour loads at a minimum which corresponds nicely with the need to be able to charge your battery bank with peak power of at least 5-10% of bank size. So for 11.5 kWh load plan on at least a 3kW PV array!Now if you have grid power and just want to supplement with a RE source that is fine. You can have a smaller battery bank and PV array (or wind turbine). There are "grid interactive" inverters that allow you to program parameters for when grid power is used.Outback Power, Schneider Electric, Victron and SMA are leading brands.

author: calexanian
author_rank: Super Contributor
timestamp: September 03, 2014, 04:50:27 am
content: Invest in a solar charge controller. They are readily available now and have a nifty switching converter that will take the peak efficiency voltage of the panels which varies but is anywhere from 20 to 40 volts depending on design and spits out a AGM, gel cell, or deep cycle battery friendly voltage and charging current. Most house type modules are 180 to 300 watts and several of them together with an appropriate charger to 12 volts may suit you well. All off the shelf. I see this kind of setup in mobile communication often and 480 stand by watts is not unusual in any way.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: September 09, 2014, 07:38:17 pm
content: Thanks mtdoc, i want it to be part grid and part re source and the grid interactive inverter is just what im looking for.Im only doing this for a hobby, if it fails it dont matter. Just one question as you seem to know what your talking about, Do I use the12volts strait from the batteries or use an inverter and a power supply?.cheers

author: mtdoc
author_rank: Super Contributor
timestamp: September 10, 2014, 09:06:02 pm
content: Quote from: snipersquad100 on September 09, 2014, 07:38:17 pmWell if the only load you plan to run is the 12V 40A load then you certainly could run it direct from the batteries. That would be the most efficient way.Of course if you plan to have a grid interactive inverter/charger hooked up anyways so that you can charge your batteries with grid power when necessary then running your load from a power supply could make sense.Modern inverters typically achieve 92-95% efficiency. You'll obviously also have losses with the power supply - much less with a switching supply than a linear one of course.Just to get an idea - with my PV system (gridtied with battery back-up and Outback GVFX 3648 inverter) I see an average of about 82% efficiency from PV power at the charge controller to household loads. This number reflects the sum of all losses including battery charging/discharging, wire losses and inverter losses. You could probably achieve similar with a good switcher power supply run off the inverter. My WAG is that if run directly from the battery you'd be closer to 90% efficient.

author: johansen
author_rank: Super Contributor
timestamp: September 11, 2014, 04:17:50 pm
content: better yet, invest in a better ponzi scheme