Author Topic: cooling fans & controls  (Read 7047 times)

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kitestrings

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cooling fans & controls
« on: October 02, 2014, 11:45:10 AM »
So I've now got most of the parts & pieces needed to assemble my resistive load bank.  The latest find - I dumpster dove (it was sitting on top really) to recover the remains of a 100A transfer switch.  I mainly wanted the box, but if anyone needs parts for a Generac 100A auto transfer switch let me know.

Okay back to the topic.  I've got a box now that measures about 7 or 8" x 13" x 28".  I have my six wire-wound resistors (~18" long), and I have a 3-pole DIN rail breaker.  My plan has been to cut large ventilation holes top and add a muffin fan, or blower, in the bottom with a simple snap-disc thermostat for control.  I'm trying to decide on a fan, but there are lots of choices.  I'd thought DC muffin fans were generally quieter, but I have ready access to AC or low voltage DC.  There also are VSD units, but I'm wondering if it is necessary.  I thought I might start with a small auto blower on a chopper DC dimmer/speed control I've got (both).

Hard to know how much heat there will be, but on occasion, when the batteries are full, and the diversion load is satisfied, we could be dumping ~4+ kW.  I'm curious what folks have used and been happy with, and any recommendations on a starting target for CFM and temp settings.  It will be an insulated but unheated crawl-space which is relatively cool year-round.  On at 80 degF; off at 60F?

Thanks for any input.  ~ks

kitestrings

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Re: cooling fans & controls
« Reply #1 on: October 02, 2014, 11:51:58 AM »
I probably should have stated the overall context.  This is a load bank for a 15' axial.  It will be controlled via a MS Classic CC using the hi-limit aux control thru a SS relay.  We have it currently set up, but it is shorting the windings above the preset.

madlabs

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Re: cooling fans & controls
« Reply #2 on: October 02, 2014, 12:32:53 PM »
I'd go with the best quality fan I had, be it AC or DC. Real bearings, ggod name, etc. Then maybe start with the fan on on side and the vent on the opposite side. That will give a diagonal air flow, better than going in the middle. Then if that isn't enough cooling you can add another fan on the other side and ditto with the vent.

Since I'm a belt AND suspenders kinda guy, I'd probably monkey around with a comparator circuit to detect an open resistor. Maybe even a sail switch or current sensing on the fans too. I guess it depends on what happens if it fails.

Jonathan

kitestrings

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Re: cooling fans & controls
« Reply #3 on: October 06, 2014, 08:42:28 AM »
This is as far as Ive gotten.  The breakers a 3-pole 25A, plus a 2A single for the fan circuit - will mount on DIN rail near the bottom.  I still have to cut fan and vent holes.  I'm leaning towards a 48V ~125 CFM muffin fan.



I wonder if I can toast bagels or something ;)?

DamonHD

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Re: cooling fans & controls
« Reply #4 on: October 06, 2014, 09:03:48 AM »
Hmm, toasted bagels, and a howling gale!  Much much better than a toasted stator or battery... B^>

Rgds

Damon

Bruce S

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Re: cooling fans & controls
« Reply #5 on: October 06, 2014, 10:30:47 AM »
What? No English Muffins?
A kind word often goes unsaid BUT never goes unheard

DamonHD

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Re: cooling fans & controls
« Reply #6 on: October 06, 2014, 11:28:08 AM »
I don't regard them as especially English!

Anyhow, gimme a toasted cinnamon bagel and quit arguing...  B^>

Rgds

Damon

OperaHouse

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Re: cooling fans & controls
« Reply #7 on: October 07, 2014, 09:14:50 AM »
I built a 12V load bank a while back that was PWM.   I took a high speed diode from the output resistor and charged a large cap in parallel with a couple 12V computer fans.  Anytime the load was dumping enough power the fans would come on.  No extra wiring or controls needed.  You could do the same thing with a small converter module to feed the fan for higher dump voltages.

SparWeb

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Re: cooling fans & controls
« Reply #8 on: October 09, 2014, 11:31:37 PM »
I've done the computer-fans thing with my load bank, too.  Takes quite a lot of wind and a full battery for them to come on, but it's nice to know they're there.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

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kitestrings

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Re: cooling fans & controls
« Reply #9 on: October 10, 2014, 11:16:24 AM »
I picked up a 48V fan and I found a snap-disc thermostat that's adjustable from 90-120 degF.  I think it is 115V, but the contact is rated for 25A (resistive) so it should be fine.

I don't know that I'll go to this level, but what is the easiest way of monitoring the integrity of the individual resistors (to Jonathan's point)?  Normally a set of voltage LED's phase to neutral would work, but with pairs in parallel it is not so easy.  My KISS approach would be to just route current loops to the outside of the cabinet, label them and periodically check with a hand-held amp-probe.  Other ideas?

~ks

SparWeb

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Re: cooling fans & controls
« Reply #10 on: October 16, 2014, 12:21:31 PM »
There's still a voltage drop across each resistor.  Use the delta-V to drive each individual LED.

Another approach is to use ring-clamp taps.  Depending on the design of those resistors, you can clamp a metal ring around each one and pick up the voltage at that point.
For resistors that are 12 inches long, and dropping 12 volts, then two rings spaced 1 inch apart will have a delta-V of 1 volt between them.  To drive a LED, you could put two clamps spaced ~2 inches apart for enough voltage to turn on the LED.  Closer, if each phase of the load bank is dropping more voltage.

I'm guessing your resistors are in a "STAR" pattern, so with a common neutral at the center then you can put a single ring-clamp for each resistor an inch from the center and get a few volts there.  Then all 6 LED's will be driven independently and can use the same common return wire.

There's more fun you can have, such as watching for differential between parallel resistors with a Red LED, which would indicate a failure of one resistor open-circuit.  The arrangement I just described indicates normal operation so those could be Green LED's.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: cooling fans & controls
« Reply #11 on: October 18, 2014, 08:59:44 AM »
Quote
I'm guessing your resistors are in a "STAR" pattern, so with a common neutral


Yes, there are pairs in parallel in each phase, but the overall configuration is wye.  The resistors are about 18" and they do have the ring clamps that you've described.

Thanks SparW, this is very helpful.

I was experimenting with the fan a bit.  It is nominal 48V.  The specs show a voltage range of 24-56V (.2A, 105 CFM), but I got to thinking that when this thing is active will be mostly when we're at the upper limit, or above, this range.  The dump will limit the Vmax and indirectly reduce the system voltage a bit I'd assume, so this may not be an issue, but I could also power it at 24V.  It runs a bit slower, but quieter, with reduced velocity of course.

~ks

kitestrings

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Re: cooling fans & controls
« Reply #12 on: October 18, 2014, 09:20:21 AM »
I suppose I could also put a dropping resistor in series with it to make sure we stay below the 56V upper range.  It draws only about 6-7 watts.

SparWeb

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Re: cooling fans & controls
« Reply #13 on: October 18, 2014, 12:17:27 PM »
Yes.
In most electronic boxes, dissipating 7 watts with a resistor would be an unforgivable sin, but here, dissipating heat is the whole point of the load bank.

I put 24V fans on my load bank (2 of them) and most of the time they don't run.  When the CC is starting to shed load, the duty cycle is very low, so the average voltage seen by each fan is pretty low.  They really kick in when the wind is blowing hard and the batteries are topped off.  Haven't heard them run for a while...  summer is such a calm time here.

Your system "architecture" is different, but Ohm's law is the same, so it looks like your plan will work nicely.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: cooling fans & controls
« Reply #14 on: October 27, 2014, 09:52:34 AM »
I've got this thing pretty well rangled together except for grounding and tidying up some of the wiring.  I kind of wish the box were 3" longer, but I think it will work.



There's a hole above the thermostat so I can adjust the temp setting without opening the box.  I've got it set at 100 degF to start out.  I used SO cord for feed to this thing because the rectifier box will have to be moved (eventually).  Found a bit of antenna rotor for the fan.  It is #18, 4 conductor with shielding - more wires than I need, but nice stuff.

SparWeb

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Re: cooling fans & controls
« Reply #15 on: October 27, 2014, 11:02:38 PM »
Won't the fan get hot if it's on the top?
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: cooling fans & controls
« Reply #16 on: October 28, 2014, 08:18:35 AM »
Quote
Won't the fan get hot if it's on the top?

Yes.  The box had three fairly large knockouts in the top.  The fan I selected just barely allowed me to center and overlap them.  I thought, given the choice, that it would be better to have the breakers below the resistors where they would be presumably cooler.  The box will be mounted in a crawl-space (4 1/2' headroom) that stays ~50 degF year-round.  Hopefully the thermostat allows me to maintain safe temps.

I'm a little concerned that the breaker blanks in the cover may be too close.  They are just plastic snap-in inserts.  I think I may change to a piece of metal.


Mary B

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Re: cooling fans & controls
« Reply #17 on: October 28, 2014, 03:39:50 PM »
From the description of where you are putting that I would rig up some form of over temp alarm so you do not burn the house down. If a failure lets temps build to the red hot stage you may run into trouble. The breakers are also to close to the heating elements and if they are thermally triggered they may trip off all the time.

I would mount the breakers in a separate box spaced about 6 inches from that one. Also move the fan to the outside of the enclosure or it may melt down too.

kitestrings

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Re: cooling fans & controls
« Reply #18 on: October 29, 2014, 06:29:06 AM »
I'm having all the same after-the-fact second thoughts on this thing (why's it so much easier in hind-site?).

I've been thinking I could move the breakers out of, or close-nipple a separate smaller box to the enclosure.  This would allow me flip the box and reverse the fan (so it is outside the enclosure, blowing up and into the elements).  Does that sound better?

clockmanFRA

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Re: cooling fans & controls
« Reply #19 on: October 29, 2014, 01:12:56 PM »
Hi Kitestrings,

Don't underestimate the heat given off by those dump loads.

Here's one of my early designs, that took a full 2kw on just 2 of those heaters for 3 hours.  :'(

As you can see the heat transferred through the heat resistant cement board stuff across a 6mm air gap and set fire to the 18mm/3/4inch ply support board.

I now have 2off 4kW dump loads on movable steel cradles that can be put in places in the house but not touching anything.
Everything is possible, just give me time.

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Mary B

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Re: cooling fans & controls
« Reply #20 on: October 29, 2014, 02:31:14 PM »
Much better getting things away from the heat than not. Long term exposure to heat can crack plastics in the breakers, change their trip points, destroy one or cause it to fail closed...

kitestrings

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Re: cooling fans & controls
« Reply #21 on: October 30, 2014, 09:31:41 AM »
Wow, clockmanFRA that is truly scary looking. I hope you were there when thing got smokin'.

Yes, what most concerned me about this was that seemingly the one flammable component, the fan, was on the top and probably too close to the elements.  In our case we're potentially dumping up to about 15,000 BtuH.  If the fan and control worked flawlessly, it might never bother - a big if though.  I was envisioning the worst case that the fan turns to melted goo, and starts to cook...

I started rearranging it a bit.  With the fan below, and outside the box there should be 4-5" clearance at presumably the coolest section of the enclosure.  On the top then, I'd have more clearance and the largest amount of free-air vent space above the elements.

I suppose I could also raise the front cover on stand-offs, but I wonder if this would reduce a more directed stream of air over the fins?

SparW, Mary, clockman, thank you for your candid, constructive comments.  ~ks

Mary B

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Re: cooling fans & controls
« Reply #22 on: October 30, 2014, 01:51:28 PM »
Creating  gap around the lid will ruin airflow BUT mounting multiple fans on the lid blowing across the resistors  would be a better way to cool. As it sits one end of the resistor will be cool, the other end baked by the hot air that is being pushed lengthwise along them.

kitestrings

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Re: cooling fans & controls
« Reply #23 on: October 30, 2014, 07:46:54 PM »
Quote
mounting multiple fans on the lid blowing across the resistors  would be a better way to cool

I don't think that is an option.  At least not with this box.  There's just no way to get close to a safe clearance to the thing(s).  This may be the best I can do with these components.  Gotta think about it a bit more.

A few related variables:

The air temp being moved is pretty low temp compared to something sitting at room temperature like a printer, PC, or even space/room heater.

The resistors are wire-wound, with an open porcelain core.

The Classic CC has both PV(Vin)-high adjustable settings, but also delay/hold.  So, once the set point is reached one can select a lengthy delay.  Assuming we actuate at a safe input V it should load the thing to where the rpms are limited, not unlike when the windings are shorted (a popular mode that I dislike immensely).  It is possible then to program a timeout, resume, and if necessary repeat.  Still the wind has a MO that doesn't always adhere to anything "normal"; I'm well aware.

~ks

SparWeb

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Re: cooling fans & controls
« Reply #24 on: November 01, 2014, 11:11:01 PM »
My current diversion load has fans on it.  They are near the bottom, on the door in a separate duct so that even if they're off, they won't be cooked by the heat.

I'm really surprised I don't have a picture handy - I usually snap a few pix when I set stuff up like this...
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: cooling fans & controls
« Reply #25 on: November 10, 2014, 09:36:02 AM »
A quick update - this is my latest attempt:

Without starting from scratch, I've inverted this box so that the fan is now on the bottom.  There is nothing combustible on top now other than the wire insulation at its upper limits.  I moved the breakers to a separate box and took the fan wiring to the outside of the enclosure.  I moved the fan to the outside (and now below) the enclosure.

Powering it with 48V - 58V or so when we're dumping - it moves quite a bit of air thru the thing.  There's a few small holes to fill with hi-temp sealant, and I want to put some v-profile weather-stripping on the cover.

I also just need a small piece of sheet steel to cover the breaker spaces in the cover and I think this is ready for a test drive.




Mary B

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Re: cooling fans & controls
« Reply #26 on: November 10, 2014, 02:40:38 PM »
Looks much better, getting the wiring out will cut down on brittle wires breaking off in a few years as the heat does them in.

SparWeb

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Re: cooling fans & controls
« Reply #27 on: November 17, 2014, 01:04:01 PM »
Looks really good now.
In my experience, the weather stripping may get hot enough to "glue" the lid on.
Silicone would resist the heat better - don't know if hardware stores have that, but maybe somewhere in the furnace ducting section...
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: cooling fans & controls
« Reply #28 on: November 17, 2014, 01:25:39 PM »
Thanks Spar, Mary.

I couldn't find the stuff I was looking for - on some older style wood casement windows they used to use this preformed aluminum strip.  It had no adhesive, but just was press-fit into a saw kerf at the perimeter of the sash.

Anyway, I screwed a piece of galvanized sheet steel over the open circuit breaker spaces in the cover, with a small bead of sealant, and plugged any remaining smaller holes with hi-temp sealant.  I do want to be able to open the cover for inspection(s).

This weekend I mounted it in place and ran the wiring upstairs.  Just got to make terminations and we should be ready.

~ks

Mary B

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Re: cooling fans & controls
« Reply #29 on: November 17, 2014, 03:49:40 PM »
McMaster carries silicone rubber sheeting that makes good high temp gaskets.