12V DC Inline Blower & AC/DC Power Supply

[fizzix]

Nothing works better than success! Glad you got it going.

[NineInchNails]

I'm really glad this power supply works. I'll install an inline fuse soon. I'll likely start with a smaller fuse and hopefully it doesn't burn out over time. It says right on the blower to install a 5A fuse though.

[Fivey]

I would use a lower amp rated fuse, maybe a 1 or 1.5, but certainly not 5, as it will be way overrated to your blower with is rated at 2.5A..

Mars

To disagree with Mars, and I hope an explanation will clarify things: you need a fuse that is over-rated above the operating current of the device. If it draws 2.5A and you put in a 1.5A fuse, when the pump draws 2.5A as it is supposed to, the fuse will blow.

The fuse is there to deal with NON-operating failure conditions. So in the case “something” goes wrong, and the circuit starts drawing more than the operating current, the fuse will blow and cut the circuit.

You don’t want to massively over-rate the fuse, eg 50A, but a slow-blow 5A fuse sounds fine.

[NineInchNails]

I would use a lower amp rated fuse, maybe a 1 or 1.5, but certainly not 5, as it will be way overrated to your blower with is rated at 2.5A..

Mars

To disagree with Mars, and I hope an explanation will clarify things: you need a fuse that is over-rated above the operating current of the device. If it draws 2.5A and you put in a 1.5A fuse, when the pump draws 2.5A as it is supposed to, the fuse will blow.

The fuse is there to deal with NON-operating failure conditions. So in the case “something” goes wrong, and the circuit starts drawing more than the operating current, the fuse will blow and cut the circuit.

You don’t want to massively over-rate the fuse, eg 50A, but a slow-blow 5A fuse sounds fine.

Sounds good to me. That's what they recommend anyway. Thanks for the input too!

[heynonny]

Do yah have a regular auto battery charger?? They usually put out ± 14 volts, plus, iffin its got a gauge, you might see an initial 'surge' of current.

Actually, to me, it seems the blower is at fault.

[Tony1964]

Just reading this through, and whilst late, after you have found the problem, here is something that would have concluded your issue earlier.

You obviously, as I have read, tried the blower on a car battery, you seem to know what your doing, so, if you put a DC current meter in line with the car battery, you will see the start up current, assuming you have a DC current meter that is, and one that can read to that level of DC current.

I am surprised that it has a start up current so high, but, hey, your done know, well done, but, for future referance.

Cheers

Tony

[still_stirrin]

I am surprised that it has a start up current so high....

Yes, but it is not surprising that the current leads the voltage, as that’s the way inductive circuits work. The correction is to add a capacitor to the device so it pulls the circuit reactive. Big motors often have capaitive starters for this reason.

However, it is surprising that a simple DC motor would require this because typically the windings are not so long as to create the inductance of a large winding. DC motors, especially low voltage motors, typically don’t require “start up” capacitors, sometimes called “condensers”, as is the case with your home’s air conditioning compressor unit. They usually do require a starting capacitor.

A starting capacitor provides the “start up current” flow as the voltage developes across the copper windings (an inductor).

A power supply with a large transformer also has energy “stored” in its voltage stabilizing capacitors which will give you the “in rush” current to start a motor.

On the other hand, a switching power supply is designed to supply voltage, allbeit - a very well regulated voltage, but it can’t support the “in rush” current needed for an inductive load, like a big motor.

Electricity...it’s a SHOCK sometimes.
ss

[NineInchNails]

I don't claim to know or understand the differences in power supplies, motors, how to identify type of motor or how to determine which type of power supply technology is required for which motor type. I just knew I had a 12V DC 2.4A motor and tried to find an appropriate power supply. After Googling quite a bit about this very type of blower and which power supply would be appropriate, I saw many instances where people say, "any should work as long as it is rated for more amps than the blower calls for". I didn't find an instance where someone pointed out a specific power supply and said that it worked on this type of blower. I found one instance where someone said their blower twitched like mine did, no solution so I just hoped it wouldn't happen to me. It did. Hopefully this thread will help someone out in the future if it comes up in their Google searches. Hopefully this power supply/blower combo operates for a very long time. This has been helpful and educational for me. I still don't fully understand the internal technicalities, but I have a better, while vague, kind of understanding now.

[Tony1964]

SS

Inrush current compensation something like this in the image, not as it matters anymore, charge via R1, say 10 Ohms, and fast discharge via D1, vary the capacitor dependent (within reason) on the start up current assistance required.

Cheers

Tony