powering a solar pwr'd motor at night.

kenbo90August 2, 2012

Hi, ive been trying to power a 30watt solar attic at night with a 30v/5A p.s. The p.s went a week running at 25v before it 'blew up', it won't go over 7v now. I didn't have a diode in the ckt, should have I used a lower voltage/higher current ac_dc converter instead? I was looking to speed up the fan when using utility pwr vs the 17v it runs on during the day(there's a pass through to the bedroom below if your wondering why). Opinions?

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brickeyee

What is the fan motor rated for?

was the voltage correct?

AC or DC motor?

AC or DC power supply?

Way to many unknowns to offer any advice.

    Bookmark   August 2, 2012 at 1:32PM
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kenbo90

What is the fan motor rated for?
The motor has a rating of 36v/13a, that's at least what was printed on the label when I had it apart.

was the voltage correct?
The fan at full solar power is running at 17v and with a measured inductance/resistance of 10ohms, which puts the amperage at less than 2a, which makes sense that the rated solar panel is 30watts.(that have a 50watt panel, so I assuming it uses the same motor)
AC or DC motor?
Got to be DC, only thing connected is the panel and I ran it with a 30v DC power supply.
I was running it at 25volts, but i wasn't raising the voltage, I just turned on the juice from the previous setting. It wasn't giving me any indications that there was any over voltages/currents. I can't see the motor having a major startup current requirement because its fairly small and it runs on as little as 5 volts(very slowly)but now that I thought about it the voltage builds in the panel as the sun rises, so oops...

    Bookmark   August 2, 2012 at 2:25PM
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kurto

There are some inconsistencies in your information. If the fan is 36v/13a, then it's really a 468 watt motor. How were you running a 30V power supply at 25 volts? It sounds like the fan was attempting to draw more power than your power supply could provide.

    Bookmark   August 2, 2012 at 2:50PM
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lbpod

Don't any of you Jamoaks realize that you can't run
solar powered 'anything' at night? Obviously this system
has some batteries incorporated.....DUHHHHH

    Bookmark   August 2, 2012 at 3:37PM
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weedmeister

I think I can run a DC motor at night with a DC power supply of sufficient size, solar or not.

I'm going to guess that the 36v/13a is actually 36v/1.3a. This would make a lot more sense.

    Bookmark   August 2, 2012 at 3:58PM
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kenbo90

Sorry, if it wasn't clear enough. I rewired it... the fan has the ability to run off the panel or any other power source that i connect to the input via a 'flick of the switch'.

    Bookmark   August 2, 2012 at 3:59PM
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Ron Natalie

Without knowing the rating of the motor (or the solar cell) we can't really venture a guess as to what the power supply requirements would be or why your first kludge blew up.

    Bookmark   August 2, 2012 at 5:10PM
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brickeyee

" I rewired it... the fan has the ability to run off the panel or any other power source that i connect to the input via a 'flick of the switch'."

What panel?

This is not making a lot of sense yet.

If it was 36 V, 1.3 A (that current sounds about right for a solar powered fan unless you had HUGE solar panel) it shold have been fine.

DC is DC, so if you had a DC supply hoked up correctly it might have run a little slower at 30 V if it was a DC permanent magnet fan with brushes.

If it was a more modern fan with a stepper motor ad no brushes it may well have tried to pull more current at the lower voltage.

    Bookmark   August 2, 2012 at 5:19PM
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kenbo90

Guys,
The motor is rated for 1v to 36v. I'm not sure of the amperage but either way. I ran it with the power supply at 25v/3a because the power supply is a rated 30v/5a and at 25v the fan is very spinning pretty damn fast and that would be just above the voltage equivalent if I had bought the 50watt solar panel(they use the same motor). The 30watt solar panel has a peak voltage reading of 17volts during the day and with a 10ohm reading across the motor, that would give me approx 1.2amps. At this point i'm assuming that just turning on the supply at its 'set' voltage and not slowly turning up the voltage had an effect on the operation of the supply. agreed? then we can move on to the next question.

    Bookmark   August 2, 2012 at 5:49PM
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brickeyee

It is very likely the current draw changes inversely with the applied voltage.

Low voltage, high current.

Higher voltage, lower current.

While it wl not harm a solar panel, it will kill a 120 VAC to low voltage DC power supply, especially long term to try and draw more current than it is designed for at any specific voltage.

A 30 V 5 A power supply is very large.

i wold bet it can deliver either 30 V at a low current, OR 5 A art a low voltage, but not both 30 V AND 5 A at the same time.

That would be a 150 W output supply.
Not small or inexpensive.

At the lower voltage you fired you power supply.

    Bookmark   August 2, 2012 at 7:20PM
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kenbo90

Mastech Variable Bench Power Supply 30V 5A HY3005D is what I bought. The question now is how do I go about making the project work, another supply, converter? Should I be putting a pot in series and a diode across as a way of filtering the ckt and reducing the shock that the ckt will see when the initial startup occurs?

    Bookmark   August 2, 2012 at 7:46PM
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lbpod

OOPS,sorry. . . I missed the part about using a DC
power supply. You'se guys aren't Jamoaks after all,
I guess I am.

    Bookmark   August 3, 2012 at 9:56AM
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kenbo90

Duly noted... Any proper insight?

    Bookmark   August 3, 2012 at 10:08AM
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weedmeister

With that power supply, the current controls are not for current SUPPLY but current LIMIT. I would set the current limit to max and control the fan speed with voltage.

    Bookmark   August 3, 2012 at 3:47PM
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brickeyee

" the current controls are not for current SUPPLY but current LIMIT."

It appears o have a constant current mode.
You do not want to use that mode.

It appears physically large enough to have a 150 w output capability (5 amps at 30 volts).

Put t in voltage output mode (NOT constant current and the current controls should then be the current LIMIT.

Set the limit to max.

Adjust the voltage.

You still need to find out exactly what kind of motor the fan has.

If the surly has an current display make sure it is NOT going even near 5 amps.

It looks like a cheap Chinese supply.
Their reliability is always suspect, and their displays not all that accurate many times.

Use a separate volt meter to check the voltage wen setting things up.

Loading it to more than 80% of its rated output power is going to be iffy (not uncommon on all but very expensive supplies).

Make sure you are not back-feeding the solar panel with the bench supply.

When the bench supply is providing power one of the panel connections should be open.

    Bookmark   August 3, 2012 at 5:10PM
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kenbo90

I know the ckt is good, sources are seperated like a transfer switch. Its just feeding it is my issue. Im going to return the supply (sorry Amazon) and get another. Ill look for bigger and better, suggestions? If this was your project, what would you do?

    Bookmark   August 3, 2012 at 6:32PM
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dkenny

got a 12v battery..maybe one from a UPS..you just need it for a little while..

replace the power supply with the battery..does the fan run correctly? if yes..now put a 2ns battery in series with the first..then measure the current..more or less than 5amp?
if less your power supply isn't the problem.its how you're trying to use it. X2 in putting the current setting to the MAX..start with the voltage at 0 and slowly increase it

just some thoughts

    Bookmark   August 3, 2012 at 9:43PM
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kenbo90

Thank you guys for the help. So it seems the census is to get another supply and not just turn it on with the settings in place.. No thoughts on putting two coverters in series like two 13v/13a and control the load with a large pot 0-100k or do you think ill fry the motor with that much current capability?

    Bookmark   August 4, 2012 at 9:02AM
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brickeyee

"If this was your project, what would you do?"

Use a battery and a trickle charger.

Make sure the charger will not be damaged by leaving it connected when using the battery, or wire up a multip pole switch to connect (ad disconnect) the charger, the battery, and the trickle charger with a single flip of one switch.

A DPDT switch would be a likely starting point.

Make sure it has a high enough contact voltage and contact rating for DC.

Without the cycles present on AC, it is harder to switch a higher current DC circuit open (off).

    Bookmark   August 4, 2012 at 10:01AM
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kenbo90

Like two 12v/10ah batteries in series and a 24v trickle charger?

    Bookmark   August 4, 2012 at 1:23PM
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lbpod

Those adjustable bench-top power supplies are not meant
for continuous use. Get yourself a dedicated power
supply. Google 'power supplies' and you will see
bazillions of them. My favorite place for them is
MPJA, see link below.

Here is a link that might be useful: D.C. Power Supplies

    Bookmark   August 5, 2012 at 9:34AM
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brickeyee

"Like two 12v/10ah batteries in series and a 24v trickle charger?"

Trying to use a higher voltage trickle charge on batteries in series does not work all that well.

More useful systems trickle charge the batteries separately since they do not math in current or voltage needed to trickle charge.

One of the batteries in either a series or parallel trickle charge setup will b\e overcharged.

Right from the start batteries have minor differences, and with repeated use and charging cycles they get further apart in their charging needs.

The common electrolyte in a typical multi-cell lead acid battery helps make the cells 9at least0 withing a single battery 'track' each other in use.

    Bookmark   August 5, 2012 at 10:24AM
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yosemitebill

The most likely cause of failure of your power supply was due to the transients and back emf created from the motor feeding back into the power supply. That supply is meant for use in testing electronic circuits that do not produce all kinds of hash.

You need to add a reversed biased diode across the motor terminals - cathode to positive and anode to negative. Something like a 1N5402 should work. That will snub the back emf created when the power is shut off.

You also want to add something like a .47ufd/100v mylar capacitor across the terminals as well to filter out some of those transients that the motor produces when running.

From there just get an inexpensive DC power supply rated around 18-24VDC and about 2-3 amps and it should work fine.

    Bookmark   August 5, 2012 at 12:03PM
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countryboymo

With the proper use of diodes a person could use two batteries in series 24v but still charge them with a 12v trickle charger with the charger in parallel. No wait a minute would diodes even be necessary if a person just made a series/ parallel setup? The charger would just need to provide enough output for the two batteries and the load so they stay charged.

    Bookmark   August 5, 2012 at 1:41PM
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kenbo90

Hey Ya'll. Just wanted to say thanks for the input. Hopefully it works this time, I'm looking to put this project to bed.

    Bookmark   August 6, 2012 at 5:11PM
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lbpod

Amen, Bro. Let us know what you did to finally
put this project to bed. 'WE' are curious.

    Bookmark   August 7, 2012 at 1:48PM
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kenbo90

Hey Ya'll, I'm back with an update and a new question. First, it turns out the bench supply I used did not actually fry itself but went into a constant voltage memory status, that needed to be cleared by multiple on/off switch cycles. In the meantime I purchased a 60w(24v/2.5a) single supply that i tried to use but had to return because it just didn't have enough pwr. The inrush current was just to high. So I got a 100w (4.5a) and it worked well. I also put a diode and cap in parallel. Now forward a month, it stopped working. It seems that the 100w doesn't have enough pwr now. Im assuming its the overvoltage light is blinking and the fan doesn't spin that fast. The solar panel ckt doesn't move it neither. Can a sign of a bad motor/brushes be that it needs more juice? The fan blade never looked like it was balanced right and Im curious if that might have taken its toll on it.

    Bookmark   September 5, 2012 at 4:19PM
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