SpudFiles

I tried to do some research myslef but It seems I know nothing about electronics...

I have a 24V 7W solenoid... how many 9V batteries would I need to operate it without any problems ?
my guess is that 3 joined in series would be enough (at least as far as voltage is concerned) but would there be enough current ?

Power (Watts) = Volatge x current

so if your solenoid is 7W, then 7/24 = current.

so by my calculations, you need 0.29 amps.

hmmm but how many amps can one 9V battery provide ?

joining them in series would give me 27V, but their amperage would be equal to one 9V battery and they would last 3 times longer.... (I hope I get it right?)

POLAND_SPUD wrote:hmmm but how many amps can one 9V battery provide ?

joining them in series would give me 27V, but their amperage would be equal to one 9V battery and they would last 3 times longer.... (I hope I get it right?)

i'm not sure of the current of a 9v battery, although i would have thought it would have been above 0.29A, i'll see if i have one and i'll have a look.

edit: ok i found an energizer 9v, and it doesn't mention the current... so has anyone got a 9v and an ammeter lying around?

Batteries are constant voltage sources, this means that they'll provide current based on a function of voltage and resistance (V=IR).

The more current you draw, the faster the battery will drain, DO NOT short the contacts with an ammeter. This is effectively shorting out your battery: It will lose it's charge very quickly, heat up, and I've heard stories of them exploding

0.27A is well within a 9V's ability. Especially since it'll be turned on for a second or so. Go fer it

Edit: A quick google search found the mAh (how long it can sustain a certain current) rating of some common batteries:

http://www.powerstream.com/9V-Alkaline-tests.htm

thx TurboSuper

A typical fresh 9V battery will source 1 to 2 amps. It'll only do that for a few seconds though. At 0.3A it'll last a lot longer and should be fine for your application since you'll only be energizing the solenoid for a short time.

It is likely that the solenoid will work on any voltage from about 5V up to 30V or more. Two 9V batteries in series should be enough. Three is fine but I doubt it'll perform any better than two.

It will pull .29 amps only if you apply the full 24 volts. At 9 volts, your going to pull only .108 amps, 18 volts you will pull .216 amps, and at 27 volts you will pull .324 amps. All within the operating range of fresh 9 volt batteries.

Edit: A quick google search found the mAh (how long it can sustain a certain current) rating of some common batteries:

http://www.powerstream.com/9V-Alkaline-tests.htm

ahh... so thats what mAh means... i've always wondered.. but never looked it up

ALIHISGREAT wrote:ahh... so thats what mAh means... i've always wondered.. but never looked it up

FWIW -- mAh = milliamp hours. Also Ah = Amp hours

I'm assuming that this is for a sprinkler valve. I use three 9-volts in series and it works just fine.

man_o_brass wrote:I'm assuming that this is for a sprinkler valve. I use three 9-volts in series and it works just fine.

I use two 9Vs in series and it works fine.

Anyone tried a single 9V?

I've heard of people using 12v but im not sure... I wonder how well it would work with a single 9v.

uhmm acctually it's for a solenoid spool valve (this one --> http://www.spudfiles.com/forums/solenoi ... 16722.html )... but their principle of operation is the same

jimmy101 wrote:Anyone tried a single 9V?

It opens the solenoid only partially, and more slowly.. It works on triggering a sprinkler valve, but not all that great. Comparing two batteries to one, you will see a difference in the valve's performance.