9V batt project - even need a fuse?

Thread Starter

bio88

Joined Feb 17, 2011
34
Got a small 9V battery project that is basically a switch and a small DC solenoid. Would you recommend a fuse and if so what size?
 

debjit625

Joined Apr 17, 2010
790
If those small 9V 500mAH batteries then no need of a fuse.Just keep it simple.But using a fuse will not do any bad, so if you want to add it you have to tell us the current rating of the solenoid.

Good Luck
 

debjit625

Joined Apr 17, 2010
790
So that gives us 9/40 = 0.225A or 225mA,their are fuse available but I don't think you will need any fuse for that unless you are using a very large battery capable of delivering a huge amount of current which could cause fire in a situation of short-circuit .Else if it's a small battery like used multimeters then not much will happen in a situation of short-circuit just the battery may warm up a bit and drain all the charge.

Good Luck
 

Adjuster

Joined Dec 26, 2010
2,148
It may be useful to consider what a short working life you can expect from such a battery. 9V applied to a nominally 12V coil relay will barely pull it in - in fact it may not work, even when the battery is new. The battery voltage surely cannot fall far before the relay will not work.

Unfortunately, you are proposing to use the battery with a much bigger current drain than it is suited for. Even taking its capacity at its face value, you could only hope to get a couple of hours, and to make matters worse the Ampere-hour capacity gets worse at excessively high current drain. You might therefore get less than an hour of function with a PP3. If that is not acceptable, use a bigger battery.
 

Thread Starter

bio88

Joined Feb 17, 2011
34
Thanks for the help! The solenoid only needs to energize/actuate to end of stroke. 9V gives me just barely the ness. mechanical force. Although more force is always better!

Need to keep the circuit very safe and consumer level battery-wise. Don't want to burn anything down : )
 

rmnorton2

Joined Oct 12, 2011
1
bio88-
sounds like you might have already done what I am trying to start. What stroke is your solenoid? Where did you find it?
I need a simple push solenoid with a stroke of an inch or more and would like to run it off a 9v battery. Will need to push a few pounds for a brief moment. Is this realistic?
 

Butterworth

Joined May 6, 2009
135
bio88-
sounds like you might have already done what I am trying to start. What stroke is your solenoid? Where did you find it?
I need a simple push solenoid with a stroke of an inch or more and would like to run it off a 9v battery. Will need to push a few pounds for a brief moment. Is this realistic?
I think it would be more realistic to use 8-AA cells, rechargable if you must, but those will only give you about 9.6V (at a mAh rating from 800-1000mAh), if you use Alkaline, you will get about 12V(+/-) at a regular mAh rating (around 500mAh or less?).

So its up to you to try:
  1. More voltage @ lower mAh capacity, or,
  2. Slightly higher voltage @ higher mAh capacity?
 

ErnieM

Joined Apr 24, 2011
8,377
If you put a small signal diode such as a 1N4148 you can get reverse voltage protection (if you put the battery in backwards) and it may also act as a fuse when need be.
 

wayneh

Joined Sep 9, 2010
17,496
To consider the worst case, assume the user uses a 9V rechargeable and manages to short it. I think the old nicad batteries will deliver the highest sustained current. I suspect shorting one actually would create some risk of burns or even fire. A fuse is never a bad thing, except for the cost and footprint.
 
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