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Old May 13, 2012, 07:35 PM
ltc
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^^
Clean, basic circuit.
My only comment would be to add some local AC feedback around the op amp.
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Old May 13, 2012, 09:57 PM
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10 LM317's = $5 = 250 watts
It's hard to beat that with any other type of circuit, plus you get excellent temperature protection. Barring reverse polarity and overvoltage, it's not easy to destroy an LM317. The best part is that it's a very simple circuit that anyone can implement.
That is a nice simple circuit also Ian, thanks for posting.
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Last edited by spog; May 13, 2012 at 10:36 PM.
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Old Jun 02, 2012, 12:09 AM
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Hey Spog,
Figured I would post some stuff about my discharger over here. By the way great discharge load. Like Spog has said in previous posts the LM317T is super cheap and very good for this. I picked mine up for $.33 a piece.
I took Spog's load idea and JJ604's cut off circuit and modified them to meet my needs of a 3s/6s selectable auto-cutoff discharger. The cutoff circuit is powered by an AC/12V transformer or a 3S Lipo. The default load is for a 3S battery and the green toggle switch changes the load to 6S batteries. I am just adding more LM317 regulators to the load with the switch. All it takes is a single regulator for the 3S battery and five regulators for a 6S battery for my set up. It will take a 3S 2200 mah and a 6S 5000 mah battery from fully charged to storage voltage in 20 minutes with a consistent 3.85V per cell when done. I experimented with the number of regulators for each battery size and came up with the best combination of regulators at a descent discharge time with a consistent cutoff storage voltage. The 3S battery discharges at a load of 2.2 amps and the 6S battery discharges with a load of 6.5 amps.

JJ604's cutoff circuit
http://www.rcgroups.com/forums/showthread.php?t=1131817
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Old Jun 02, 2012, 01:59 AM
ancora imparo
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If you don't want to do less than 3S, you can dispense with the 12v plug pack or separate battery.

Just use one more 33cent LM 317 and a couple of 1cent resistors as a regulated 12V supply.

It will supply more than enough current for the relay and fan. Probably about 300-400mA max which even dropping from a fully charged 6S will be less than 5 watts dissipation.

John

PS I was thinking of knocking one of these up myself with the cut off and variable number of loads. Do folks think it is worth a proper construction article? Be written so non-electronic types can build it. Along the lines of the simple cut-off.

Interested in what people think.
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Old Jun 02, 2012, 02:19 AM
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Hey John,
I would be interested in seeing a full build article on making one of these dischargers. Can you give me some more information on using a regulator and resister to make a stand alone unit with the discharge battery as the 12V power supply.
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Old Jun 02, 2012, 03:52 AM
ancora imparo
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Do better than that. I'll just knock one up and see if it works OK over the voltage range you want.

Stay tuned.
Quote:
Originally Posted by pctomlin View Post
Hey John,
I would be interested in seeing a full build article on making one of these dischargers. Can you give me some more information on using a regulator and resister to make a stand alone unit with the discharge battery as the 12V power supply.
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Old Jun 03, 2012, 03:58 AM
ancora imparo
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Melbourne, Australia
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Using an LM317T to drive a discharger relay and load fans

OK, here's what I found.

I used a LM317T regulator set up to supply a nominal 12.5Volts.

See attached picture.

I varied the supply voltage from 0-30V and measured the current and output voltage driving a typical 60Amp 12V auto relay and a standard Intel cooling fan.

Results are in the table.

Note the figures in italics are calculated since my lab supply only goes to 30V. Also the LM317 power dissipation figure are using the relay only since this experiment showed you wouldn't need a fan on a heatsink for a simple disconnector.

Bottom line.
1) Disconnector
For batteries from 3S to 8S a single LM317 on a passive heatsink is perfectly adequate to drive a 60A auto relay. My relay will close positively at 7V which requires 8.8V In and is well under the minimum you will ever have a 3S battery at. On 4S and above the LM317 supplies a full 12V.

2) Load
The computer CPU fan is rated at 0.4A but in fact draws only a little over 100mA at full speed. For 3S to 8S a single LM317 on a decent heatsink is probably perfectly adequate to drive half a dozen cooling fans or more. On 3S the fans will not run at full speed but should be adequate IMO.

WARNING: It should be obvious but you cannot mount the LM317 supplying the 12V on the same heatsink as the LM317's that are the load (because the Out is connected to the tab).

John
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Old Jun 03, 2012, 04:06 AM
ancora imparo
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Melbourne, Australia
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LM317T heatsinking

For info.

The LM317T can safely dissipate up to 0.25 Watts without any heatsink.
The absolute max rating with adequate heatsinking is 15Watts

I found it was barely warm at 5W properly mounted with thermal paste on an Intel LGA1366 CPU (i7) heatsink without any fan running.

You can calculate the heatsink resistance required for any particular wattage.
A regulator is normally taken to be OK up to 60C.

Then the heatsink thermal resistance needs to be equal to:

(60-Ambient temp)/Power

Example at 25C ambient and 5 watts

You would need a heatsink with a thermal resistance of less than (60-25)/5 = 7 degrees/Watt

A typical economy twin 3" Al heat sink with fins top and bottom for a TO220 package will be about 3C/Watt or less.

John
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Old Jun 03, 2012, 09:06 AM
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Check your fan load, since different fans can vary in load current quite a bit. The fan used on my heatsink is a high rpm 80mm which draws 380ma at 12VDC. A 12V regulator with an input of 33VDC (8S) would need to dissipate (33-12)*.38 = 8 watts (not including the relay). You can mount this regulator on the load heatsink if you isolate it with an isolation kit similar to this one.
http://uk.farnell.com/multicomp/mk33...-220/dp/520214
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Old Jun 03, 2012, 09:17 AM
ancora imparo
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Good points.

Most "standard" CPU fans draw fairly low currents however. It's easy enough to measure. Just use the 10A range on your DMM. That's the one with the lowest meter resistance and will introduce negligible error in the current reading.

The other good point about using the LM317 is that it is totally self protecting. If it gets overloaded/overheated it will just restrict the current drawn and the fan will slow down a bit.
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Old Jun 03, 2012, 02:54 PM
RC Helicopter Pilot
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I made a version of this discharger and the load drops off after things get hot.
Quote:
Originally Posted by jj604 View Post
The other good point about using the LM317 is that it is totally self protecting. If it gets overloaded/overheated it will just restrict the current drawn and the fan will slow down a bit.
That's why my load drops off the hotter it gets.

Bought a fan for mine and will be testing it today.

P.S. I bought a 7812 to power my fan and some LED's.
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Old Jun 06, 2012, 09:05 PM
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How much does the load drop off as it heats up?
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Old Jun 06, 2012, 09:32 PM
RC Helicopter Pilot
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It just kept dropping from a high of about 15 to a low of just over 2A.

I added a fan to it this past weekend and it now it holds the load just fine.
I think the regulators were shutting down from the heat.

I am using the Inspector Wattmeter to measure the load and the iCharger to alert me when storage voltage is reached.
It works great.
I can pull down a fully charged 6S LiPO pack in about 10 minutes.
I had to lower the storage voltage setting to get a resting voltage of about 3.85V/call when I switch on all the loads.

Here is my version -
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Old Jun 06, 2012, 10:08 PM
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Looks really good, where did you get those heat sinks?
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Old Jun 06, 2012, 10:27 PM
RC Helicopter Pilot
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I bought most of the parts here -

http://www.futurlec.com/
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