Oatley Electronics Kit K220

[coldspot]

I'm finishing my K220

 But the "Dummy Loads" that the kit plans

call for building are just not my kind of

ideal set up. "Take some electric jug elements and double them up and cut down to 3.5 Ohm resistance in length".

 I make some from Ni-chrome wire from an old hair blow dryer but they just seem a bit on the whimpy side and I'd rather have something a lot more heavy duty. Just to be safe.

 Just look at the heatsinks I made for the MOSFETS.

 Without any they can handle a current of 7 amps.

left side view





Right side view





Side view





 Back to my question-

 I have three "Ohmite" # "6p45c" ceramic type resistors, I get 2.0 Ohm reading them, they are rated at 1.6 Ohm @ 100 Watt.

 Should I use them alone or double two together?

They are 6" long and look just like the ones "SparWeb" just posted in his diary post

"http://www.fieldlines.com/story/2008/1/26/213134/030"

I also have one "Ward Leonarc" # 160F25

 it's 8.5" and reads 26 Ohms.

 I'll reread the box next time I'm visiting my brother and get the rated info for it.

 This controller has 4 dummy load outs and I'm thinking just to put all of these on them, one on each output.

 What this controller will be controlling is an Ametek 30 for now and about 30 watts solar. I'll be adding my "CMI" 28Lb stepper very soon also, this unit has unknown output but I'm pretty sure it will be great or better than great!!!

 I'll also be putting up an 2 HP conversion very soon, (8 #29's on it)

 but by then I should be also trying to use my

"FlexCharge" "NC25A12" Divert controller but its only good for 300 Watts without spending more money.  

Thanks

[ghurd]

It is hard to measure ohms that low.  Trust the print.

The ones SparWeb posted look like 300W to me. About a foot long. Hard to tell.

The 1.6 ohm.  It will need 2 in series to take about 9A and 66W.

One will cook with 30% over the rating.

Three in series will not dump much at all with 43W.

The 26 ohm will only dump about 550ma, about 8W.

The best option with what you have, in my opinion...

Series 2 of the 1.6 ohm, and parallel the 26 ohm for one controller output.

Together they will dump about 74W total.  Combined, it shouldn't overload one of the outputs.

That really is not enough for the Ametek, but it is getting close.

The 2HP conversion will be way past what that can handle.

G-

[coldspot]

THANKS Ghurd

 I was hoping you would reply !  

I saw that the box the 26 Ohm one came from listed it as 150 Watt, (it's a smooth side type).

I also found two more smooth ones today in an old

music box Pa had from his Electronics Repair Shop.

"TY-OHM" 150W 8 Ohm NON-IND,7.5" length, (whats non-ind?)

Mounted in a pretty nice metal box with a lot of plug in jacks on the front I'll not use but great parts anyway.

 Wish my brothers shop had another 1.6 one but three was all. There is a metal shelfing 4' x 7' section there with these power resistors in dozens of types and sizes.

 What should I be talking him out of

 I've got a little 150 Watt auto heater from H/F I'd miss in my truck.       (could buy more){$11.00}

Picked up an Auto coffee heated mug around X-mas for $5.00, watts not listed and Ohm reading not done yet.

I've got a box full of "Elements", as in, little busted box heaters, (the 120 V under the desk type), old hair blow dryer, 120 v to 440 v water heater elements, electric socks, heating pad, The "Air Element",.. ect,,.. ect.

 I will be buying a 12 VDC water heating element

But I wonder about the two 600 watt Vs the single 300 Watt that are close in price???

 I also found a double loop, 12 VDC 300 watt with a 120 VAC 500 Watt, thats more money but has both voltage types.

 I read about a 3 element one that was listed as # "DS12337", "low volt water heater element".

 Was for sale at $180. !!! I don't know what country's money but, WOW!!!

 I'd rather make hot water with my dump but warm air is good also.

Thanks

[ghurd]

Non-Ind means non inductive.

The 8 ohm will dump 1.8A, or about 26W. Each.  7.5" is more than 26W, so it's safe.

"What should I be talking him out of "

Power resistors suitable for a 12V!

Ohms Law.

Volts / Ohms = Amps

So 14.4V / 8 Ohms = 1.8 Amps

Watt's Law.

Amps x Amps x Ohms = Watts

So 1.8 x 1.8 x 8 = 25.92 Watts

Or

Volts x Amps = Watts

So 14.4V x 1.8A = 25.92 Watts

Look for big 2 to 5 ohm resistors.  Check that 14.4V will be under their watt rating.

Next look for smaller, but still big, 5 to 12 ohm resistors. Check the watts they will dump.

I like to keep the watts 20% under the rating.  They still get really hot.

I like to dump 20% more than the system can make.

G-

[coldspot]

Ghurd-

Thank you again

Yes, "V=IR"

I just forget when I'm not sitting looking at my

P,I,V and R pie chart.



I did get an "General Electric","IC9033, A4L4"

Thats 33 Ohms full length,(12") but it has tabs and between any of the 6 closest together tabs,(1.25") are 3 Ohms.(12x12=144 divided by 3 gets 48 watts)

{or should I be using the 14.4 V??}

 If I used the first set, skipped a resistance section to the next tab and used these two, then skipped again, I would have three but a wire connection between them all,,..?? Would I need to open this up by cutting the wire? Or would this be OK to use that way?  

[ghurd]

Better.  Don't go cutting it up.

Not sure how many tabs are on it, but number the 6 closest together tabs #1 to #6. #1 is on the end.

Feed positive into #4, take it out of #2 and #6. It will dump about 4.8A, or 70W.

You might be able to use the last tab (15 ohms from it to #6?) as a positive, pull 3.4A out of #6, and 2.4A out of #2.

Between this one and the others, it's plenty for the Ametek and more.

I'm not clear on the math you show, and think you typoed it.  I use 14.4V.

G-

[coldspot]

Ghurd-

Again, THANK YOU!!!

But,

 Today I scored a not working Industrial plug in heater.

 "Rival", model T770/1, 120 VAC, 1500 Watts Max.



 Low, single coil element = 1.6 Ohms

 High, 6 coils,

 splitting them into three two coil units = 3.5 Ohms each set.

 Fan was the busted non working part, but a few computer 80mm or 90mm fans will work great.

 Nice solid metal case vented front and rear with enough room for many power resistors or more heater coils.

 I'm starting to think that the heater coils are sounding like a much better plan.

 (the fist set I built up came out of an old hair blow dryer 1970's type and the little coils had the right ohm numbers but looked so small and fragile).

 I now have another cheaper plastic plug in heater that I've scraped for parts and the coils are about half the size of the rival ones but much better than hair dryer ones.

[coldspot]

Ghurd-

 G.E. unit has 7 tabs total, 12"length

End with 6 tabs





Name plate





Tab 6 to 7, 18 Ohms

4. to 2 = 6.8
   
4. to 6 = 6.8
   
   

Thanks for the info on the GE unit

"I'm not clear on the math you show, and think you typoed it."   Nope.

Watts= Volts squared divided by Ohms

or

W= A Squared times Ohms

Or

W= V x A

Easy with pie chart in front of me

I will know to use 14.4 V

I'm drilling holes for this to mount inside of the

"Rival" heater box running up and down is the only way it would fit. I'll have small computer fans blowing the heat towards the fan blowing out over the heater coils.

 I have room for the other power resistors

 to mount under the heater coil inner box running sideways but more than three might get hard to have cooling fans inside.

 Do you think I should only use the built in fan power outlet on the controller or maybe an extra power source with a thermal switch??

[ghurd]

I'd use the built in one.

A thermal switch will have lag letting the resistor get hot before the fan comes on.

It's dumping anyway, so not a waste of battery power.

I read that controller runs slow enough to power a relay.  Might just wire a fan to one of the fets.

[coldspot]

Ghurd

Thanks again

The K220 has a fan power terminal.

 So I'll be using it for a couple of computer fans.

I might still add one fan that has its own temp sensor thats from a computer power supply, this one fan will be wired direct to a small SLA 12 VDC battery for an extra cooling in case things get to hot in the box.

 Now that I've cut up the heater coils, I'm short of ceramic ends to hold them in place and I just read in a different post, Tom was saying that soldering to the Ni-Chrome is out. (?) {that blows my plans}

 I might just have to try a crimp type wrap using some solid small wire to hold the power in wire thats wrapped also,,..  ??

:|

 

[ghurd]

Hot connections are my latest problem too.

I've seen factory stuff go open at the crimp. Driers, etc.  Not corroded much, just from heating cycles (I think).

Cooler is always better.

Cooler is always better^2.  It is dumping or the resistors wouldn't be hot.

Meaning an extra 5 muffin fans won't hurt.