I've just found a dc motor that might suit my needs but the motors require 6 volts, 12 amps to run at optimal speed. There are batteries that I could use, but i would need it to run for a period of time as the work would be for an exhibition.
I mostly found 12 volts 10/12/16 amps power supply, but not 6 volts 10/12 amps.
Plus as bonus, i would need 6 such motors. So i guess a i would need a total of 72 amps!!
Any suggestions on the issue of power supply? If I diy the power supply with a transfomer and some electroincs, at relatively
-middle cost? or any other possibly options?
Sounds like a pretty intense motor! I don't think they're are too many commercial products with that kind of output. There are adjustable supplies, of course, but I've never seen one with such high current capabilities.
IF they are regular brush DC motors you could just use PWM with a 12V supply. At 50% duty cycle that is equivalent to applying 6V continuously. It would be best if the power supply was a plain linear non-benchtop type as at 12V the motors might draw too much instantaneous current. A linear supply will just drop in voltage while a regulated supply might cut out completely.
Easiest would be a separate power supply for each motor at these current levels.
Doing a DIY linear power supply at 12A will require some big components and heatsinking. Make sure you know what you're getting into.
Best bet is to buy a 12 volt 1000watt motor speed controller similar to those sold by 4QD in UK. Set to operate at 50% and wire all 6 motors in parallel.
Then get yourself a couple of leisure batteries rated at 100AH each and wire them in parallel and a decent 12 volt battery charger that can feed them with a current of around 20 amps.
The batteries will supply a clean and steady supply to the motor controller and the battery charger will feed the batteries for both the duration of the show and the remaining hours to get them back to fully charged.
get yourself a couple of leisure batteries rated at 100AH each and wire them in parallel
Don't even think about wiring batteries in parallel without some sort of circuit protection like at least a series diode. This will prevent one battery trying to charge another with the resulting release of flames.
Mike
Let's agree to disagree on that one
There may be problems with the initial connection if the batteries are seriously out of balance with respect to state of charge, but this can easily be overcome to achieve the interconnection, after which they will act as one (not necassarily the sum of the individual AH ratings)
Jack
Getting batteries to share the load is not something that happens automatically. It all depends on the battery's source impedance as to what happens.
With a fairly high source impedance the battery voltage drops as the load increases and the other battery becomes the higher voltage and in this way the load balances.
BUT - a good battery has, by definition, a low source impedance. Any slight imbalance in battery voltage (and that is inevitable) will result in one battery pouring current into the other. This will cause the generation of heat in both batteries. It will also cause excessive currents to flow between the batteries that at first might not be noticed but will eventually kill the system.
I await with interest why you think it is OK to join batteries together.
This is not just a nice academic point that we can agree to differ on, it is physics. but more that that this is a forum for giving advice to beginners and advice to simply connect batteries in parallel is some what reckless.
There are some big honkin' 5V supplies out there, for older computer systems that required 5V at tens of amps. One of these may have enough adjustment so that you can crank it up to 6V.
A standard computer power supply usually has several amps at 5V, although I'm not sure of the adjustability of those.
As far as guessing you need 72A, will you really need to run all 6 motors at the same time?
I await with interest why you think it is OK to join batteries together.
Years of experience with UPS units that use exactly that design?
I have about 10 of 'em in operation right now. All of them use at least two 12V SLAs to get 24V (some use four for 48V), and nearly all of them use multiple 24V or 48V packs in parallel to increase runtime. Individual packs are fused, but the parallel packs are directly connected.
I will note all of these are SLAs and they are all the same size (voltage and capacity). Like I said earlier, I wouldn't put a 5Ah and a 20Ah in parallel.
Mike
OK, have read th article and it contains a lot of good information but the argument of problems when discharging parallel batteries by one taking excess load and the other "charging" is flawed. Both batteries are intimately connected and their terminal voltages are therefore effectively identical. Internal resistance is what governs current apportionment.
Given care and common sense (the inevitable caveat) it is possible and in many cases, well used practice, to operate wet acid cells in parallel.
As I said, on this topic we shall just have to agree to disagree
It's not just Mike
Most people consider parallel batteries as "self ballancing".
Having a word does not mean that it is a good thing.
It will of course approximate to some voltage, there is no danger of oscillation.
It will obviously not work with different kind of batteries..
It will obviously not work when a "bad one" is inbetween..
The recharging will take place without current limiting (something Mike has elaborated on in detail.)
It will undoubtedly reduce the lifespan of batteries...
The basic question beeing: What indeed is the expected lifespan in the first place
Both batteries are intimately connected and their terminal voltages are therefore effectively identical.
I think that shows your lack of understanding about electricity. A primary or secondary cell can be modeled as a voltage generator and a series resistor but that is only a model. The impedance is distributed through the generation part. Two batteries no matter how identically constructed will not produce the same voltage. Therefore when the terminals are joined current will flow from one to the other under no load conditions. This is the most damaging situation for the batteries.
When a load is connected, due to the generator impedance, current will flow out of each battery but not necessarily in equal measures. This will cause them to discharge at different rates which when the load is removed will make matters ever worst for battery to battery current flow.
