Hey everyone,
I’m working on a project that uses 4 small water pumps. They each pull about .35a each. They will only be on one at a time.
I am thinking of using a .5 fuse on their common wire incase there is a short.
Is this an ok size?
The fuse protects the wiring, not the load, what is the rating of the wires? Fuses prevent fires.
I would suggest rating the wiring for at least the stall current of all 4 motors simultaneously,
and select a fuse to match.
"
The fuse protects the wiring, not the load, "
I wish I had a dollar for everyone who doesn't know that.
This is the wires I’m using.
The power of all 4 motors running at once is .08. I believe. It’s .32a each, so it works out to 4/.32
What do you suggest?
raschemmel:
"
The fuse protects the wiring, not the load, "I wish I had a dollar for everyone who doesn't know that.
I’m new to this. I’m learning, it’s why I asked. I’m posting to help me fill in the gaps of knowledge
There are tables of current rating for copper wire. They don't agree of course(!) but something
like 1 to 2A for AWG22 (0.3mm^2) seems typical.
Do you know the stall current for the pumps? That's what you need for rating wiring and
drivers.
Its really best to just provide links to the datasheets for each piece of hardware you mention
up-front, to avoid all the cross-questioning. Pump datasheet?
There's also the issue of cable resistance - for low voltage systems this can become the limiting
factor, not the current handling, as unwanted wiring voltage drops can be significant if the supply
is low voltage and the currents are large enough.
So I bought this kit. I replaced the relays with a Uln2803a. I felt the relays where overkill for a simple product
I am powering it with the using a ld1117v33 and a 9v psu
I can’t find the datasheet for the motors, but their specs are on the Amazon post above
I’m just worried about the pumps getting shorted by water.
Your transistors will act as fuses LONG before any actual fuse opens up.
PAul
Ah, I guess that’s good, in a ‘fire safety’ kind of way. Ideally I would like a way to protect the transistor from blowing. Is there a way to do that, or am I over thinking it?
If the pump malfunctions, and water connects the leads, will it likely destroy anything?
garrathewhinnie:
Ah, I guess that’s good, in a ‘fire safety’ kind of way. Ideally I would like a way to protect the transistor from blowing. Is there a way to do that, or am I over thinking it?If the pump malfunctions, and water connects the leads, will it likely destroy anything?
If the pump malfunctions and there is water, then the water must be under pressure, already. Why a pump in the first place?
Transistors are a lot cheaper than adding lots of safety circuitry.
Paul
Your transistors will act as fuses LONG before any actual fuse opens up.
Not to complicate things, but are such things as FOLD BACK CURRENT LIMITING , CONSTANT CURRENT, and
current sensing, all of which can shut down the transistors if the current increases beyond a certain level.
I'm not trying to complicate things but only pointing out that if a fuse will not protect your circuit, you might
want to consider a circuit that protects itself..
Paul_KD7HB:
If the pump malfunctions and there is water, then the water must be under pressure, already. Why a pump in the first place?Transistors are a lot cheaper than adding lots of safety circuitry.
Paul
It’s a submersible pump. So is the seals break on it, water can easily get in. It’s a mini irrigation system. It water 4 flower pots. It’s really just so my kids can learn to solder.
I didn’t plan on making anything fancy. I figured a fuse was an easy fix, but apparently that’s not the proper use for them.
So if I understand what you guys are saying, is that if the pump shorts, the transistor will blow before anything dangerous happens?
So if I understand what you guys are saying, is that if the pump shorts, the transistor will blow before anything dangerous happens?
A blowing transistor IS a dangerous thing. It can send tiny fragments of plastic, semiconductor and metal flying at near-supersonic speeds.
aarg:
A blowing transistor IS a dangerous thing. It can send tiny fragments of plastic, semiconductor and metal flying at near-supersonic speeds.
I feel this conversation is going around in circles. What is the proper thing to do in this situation?
garrathewhinnie:
I feel this conversation is going around in circles. What is the proper thing to do in this situation?
Combine the advice in reply #1 and #9. You could also use a motor driver module which has protection built in.
garrathewhinnie:
I’m working on a project that uses 4 small water pumps. They each pull about .35a each. They will only be on one at a time.
garrathewhinnie:
So I bought this kit. I replaced the relays with a Uln2803a. I felt the relays where overkill for a simple productI am powering it with the using a ld1117v33 and a 9v psu
Those pumps are pretty water proof, and as long as it's fresh water shorting is not usually an issue (salt water is a different story).
But that parts list raises other issues.
You're apparently intending to run those pumps off 3.3V, through a linear regulator with 9V on the input. I'd simply use an old phone charger for that (5V, 2A is just about exactly what you need). I bet you have a few of those floating around your home. When using an adapter a fuse is normally not needed on the low voltage side, by the way. That adapter limits the current enough, and probably has a short circuit protection built in.
Then the regulator: that's a 5.7V drop, at 0.35A that's almost 2W of power dissipation. That's going to give you smoke within half a minute of running that pump.
Then the ULN2803, that's an old part with Darlington transistor outputs, dropping 1.3-1.6V at 0.35A current (see datasheet), which would leave your pumps with just 1.7-2V. Of course that also keeps everything from smoking, as this little voltage means the pumps won't be drawing anything near the rated 0.35A. They may not even be able to run at all due to the low voltage.
wvmarle:
Those pumps are pretty water proof, and as long as it's fresh water shorting is not usually an issue (salt water is a different story).
But that parts list raises other issues.
You're apparently intending to run those pumps off 3.3V, through a linear regulator with 9V on the input. I'd simply use an old phone charger for that (5V, 2A is just about exactly what you need). I bet you have a few of those floating around your home. When using an adapter a fuse is normally not needed on the low voltage side, by the way. That adapter limits the current enough, and probably has a short circuit protection built in.
Then the regulator: that's a 5.7V drop, at 0.35A that's almost 2W of power dissipation. That's going to give you smoke within half a minute of running that pump.
Then the ULN2803, that's an old part with Darlington transistor outputs, dropping 1.3-1.6V at 0.35A current (see datasheet), which would leave your pumps with just 1.7-2V. Of course that also keeps everything from smoking, as this little voltage means the pumps won't be drawing anything near the rated 0.35A. They may not even be able to run at all due to the low voltage.
Thank you so much for this. It was a clear response obviously written for a newbie.
I was doing some prototyping, and decided to ditch the ld1117v33. Originally my idea was that I can get more current for the pumps by using leads directly from the 9v adapter, and then stepping them down to a usable voltage. I already had those dc converters, so that’s what I was going to use.
Now that I’ve played with it, I actually get more consistent power from the 5v out of the Arduino.
So the 5v out from the Arduino splits into the positive side of each of the motors (and the com pin of the Darlington Circuit), then each of the pump’s ground goes into the Corresponding pin. I can now use the base pins to control the motors
I now use the 9v adaptor to power the Arduino, which is rated from 5-12v.
So you’re saying between the low current, and the adaptor’s built in protection I should need to add in at more ‘shorting’ protection?
garrathewhinnie:
I now use the 9v adaptor to power the Arduino, which is rated from 5-12v.
And that is going to be completely useless!
DO NOT use the Arduino as power supply for anything more than an LED or two. Its built-in regulator is NOT up to the job.
Just use a 5 power supply to power everything - including the Arduino (through the 5V pin).
Paul__B:
And that is going to be completely useless!
Can you elaborate? That comment brings up a problem, and gives me 0 context on why or how it’s a problem.
Thanks
wvmarle:
DO NOT use the Arduino as power supply for anything more than an LED or two. Its built-in regulator is NOT up to the job.Just use a 5 power supply to power everything - including the Arduino (through the 5V pin).
The 5v out is rated at 500ma, the pumps are significantly less than that, even if they are all running.
Is there a reason this is bad practice? Is this more of an endurance thing than a current supply problem?
You may be able to draw 500 mA out of it when you power it off USB - not from higher voltages as the regulator will overheat. Still it's poor practice to do so for a permanent project, for reasons of the current itself and the noise of the motor that you better keep off the board.