I know very little about solar PV. I considered that an appliance drawing more power than the panel could supply might harm the panel, so I thought it best to switch the panel out of the circuit to ensure power was only ever drawn form the battery.
I do have mains power in the garage. I will look into this solution, seems to be neather than my proposed solution!
Thanks
Much better to invest in an air compressor which has many more uses like many useful air tools and spray painting etc have many die grinders{much better than dremels} sanders, multi tools,drills,staplers, nail guns,sanding machines etc and much more
If you have mains power available, seems a very expensive way of getting
12v?Jon Parker presented the following explanation :
No need for a battery then, just a 13.8v SMPSU and only if you must have the 12v. Why not look at a small 240v compressor?
You need to study the "load" carefully, as the SMPS pricing will rapidly shoot skyward, if you attempt to get too much capacity.
The thing is, ATX power supplies come perilously close to sufficiency and ampere-capacity. There are supplies with ratings up around a kilowatt or 1200W or so. (Think 12V @ 80A and the PCI Express cables)
ATX computer supplies put out 12.0V, while a battery eliminator might put out 13.8V. When you look at this, you might say "well, surely a small adjustment will give the 13.8V", but it isn't always that easy. (Some equipment has overvoltage protection, which is integrated somewhere and shuts off the equipment if an "abnormal" value of voltage appears. The 13.8V adjustment might cause that protection to trip. A control in one part of the circuit, does not necessarily control every subsystem in the box.)
Supplies come with "expectations" about the kind of load expected.
capacitive ["5000uf max" or a similar statement, phase margin] resistive (ham radio???) inductive (motors... 10X loading from motor when rotor stalled)
Motors are particularly tricky, because of their load current behavior. When the rotor is stalled, some motors draw 10X the nameplate current. On an SMPS with electronic overcurrent protection, the time constant on overcurrent can be quite short. Which means the SMPS turns off, as soon as you flick the switch on the air pump.
On capacitive loads, the message here is about the "hobbyist" approach to electronics. To make projects constructed at home more robust, a hobbyist adds capacitors. A capacitor is a short term energy store. And you would think, "well, perfect, I slap those into my circuit, the motor 10X current comes from the capacitor, honor is satisfied". But the SMPS has an internal feedback circuit path, and if around 5000uF is added to the output of the circuit (a small amount compared to what clever hobbyists buy), this drives the control loop crazy.
As a general rule, easy public specs for SMPS do not provide a phase margin statement, and what the limit is for adding capacitors to the output. You must contact the supplier and beg for the information (like we had to do at work when buying these).
We can't "fix" the ATX supply particularly, by adding capacitors.
Ham radio operators, look for items similar to the following. Radios intended for in-car operation, need a bench supply when the radio is run in the shack at home. Devices like this attempt to solve that problem. This one happens to be adjustable, and you could, say, adjust it when a longish cable runs to your linear. Key up the linear, adjust the supply so that the linear sees the desired value on its end (13.8V or whatever).
It's harder to say, what would make a good DC power source for an inductive load.
I tried looking in the transformer catalog, and couldn't find just the right 18V transformer, to build a classic supply. This would be the "linear supply approach", different than SMPS, wasteful and inefficient if used all day long, as some parts of the regulation circuitry kick off tons of heat. Even the diode bridge rectifier can get scalding hot when used at high load, such that the diodes have to be mounted on a heatsink, as well as the regulating circuitry. The heatsinks are measured in "square inches of active area", and you might end up needing a "cubic foot of fins for cooling" if the load is high enough.
Like the SMPS, the price of implementation goes up with the ratings. The linear might withstand more abuses (such as the motor start transient), as the plus for that approach. But it will be inefficient and kick off heat, whereas the SMPS can be "80+ efficient" and "active PFC", properties the power supplying company likes. At these kinds of loads, some SMPS are efficient enough, they barely need a cooling fan to keep the smaller heatsink inside, cool.
Each approach has issues:
SMPS - unknown tolerance to motor startup current - not typically rated for inductive loads, won't say "sure, go ahead, put an X ampere motor on here". - a solution that (nominally) lasts forever, perhaps an inductive spike could damage it (I did that once, that's how I know). - a specialized SMPS could likely deal with any load type, but at a guess, the designer would charge a fortune for this ("because they could"). It's the average SMPS which is not ready for all load types.
Linear - potentially more tolerant of loading types - might support an inductive load - something you build yourself, pretty simple hookup. - a solution that (nominally) lasts forever - inefficient, at these power levels "many chunks of iron". Maybe 80 pounds weight.
Solar/battery - battery as reservoir, is very tolerant of load types. Wonderful. Already I've gone to heaven. Don't forget the fuses! Batteries take no prisoners. A friend of mine got burned once, by not following the rules ("do not wear jewelery near auto batteries"). His metal watch strap, the link pattern was burned into his wrist! Cover the battery terminals with insulators over top.
- can hook together using purchasable subassemblies. I was even able to buy clamp style terminals to fit around the round battery terminals, to cable up a battery. - can be charged by a wall powered charger if needed, and this could even be used as a substitute for the solar panel. You could hook up a "smart charger", if you could get one that starts the charge cycle again at 11.8V. (So the battery cannot be run flat and damaged by neglect over long periods of non-usage.) - big minus, replacement of battery at regular intervals, as a function of how well the charging method makes the best use of battery chemistry (sulphation). - for automotive batteries, try not to use more than 25% of the amp-hour rating - the batteries last longer if the discharge is shallow. To pump up a tire, you might not have too much trouble with this. To pump up all the tires at an auto rally, maybe not. Do the maths, once you've measured the pump and fully understand the loading it presents. More expensive deep discharge batteries are also available.
For automotive batteries, you can find info on this site, to understand some of the requirements, and then compare what it says here, to what a smart charger is doing.
At work, each company parking lot had a battery "on wheels", used for jump-starting cars with dead batteries. The device was kept at the security desk, and could be signed out. And that seemed to work pretty well. I didn't hear too many stories about "hmmph, went to use it and someone forgot to charge the battery". That way, we didn't need towing trucks prowling the lot, looking for customers :-)
Paul
PV panels can be shorted indefinitely without harm
Then your proposed panel is pointless.
NT
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