Jun 19, 2012, 07:28 AM Steven United States, CT, East Hartford Joined May 2010 504 Posts Hey jay4. If you have a 10 turn pot you can turn any mutlimeter with a 2000µA setting into a universal current measuring device that can read up to 2000A. Last edited by xandrios; Jun 19, 2012 at 08:01 AM.
 Jun 19, 2012, 04:33 PM Volts>amps United States, MN, Buffalo Joined Jul 2011 4,028 Posts So i have less than 2 inches of 18 gage wire from my posts to jacks. Can that handle 30amps for 8 minutes? Standard is rated to 15 but not sure on run length.
Jun 19, 2012, 05:50 PM
ancora imparo
Melbourne, Australia
Joined Jul 2005
9,879 Posts
stgdz, simple answer. Try it and see. If it gets too hot for your comfort replace it.

There's nothing special about wire size. It is just a resistor. Thinner wire at high currents will heat up because it is higher resistance. Nothing bad is going to happen.

The recommended wire gauges are not really about the ability of the wire to "handle" the current in the same way as a FET or other electronic device will destruct at too high voltage or current. It is to keep resistance losses low and keep the temp down to an acceptable level. This is obviously important with house wiring installed in a flammable wall for example or wiring inside a device running 24/7. That's why there are formal codes for wiring sizes in particular uses and recommendations for wiring sizes in electrical devices.

In our application here the voltage loss over 2 inches of 18 gauge at 30 Amps is significant but not critical.

The "acceptable" temp rise is really up to you but it will only get warm.

18 gauge wire is around 0.02 Ohms/meter resistance.

So total resistance of each wire is about 0.001 Ohm.

The power dissipated in each wire is the current squared times the resistance.

= 30*30*0.001

And the voltage drop will be 30*0.001 = 0.03Volts.

So you will loose about 0.06 volts of your output voltage at full current.

The wires will get warm but not hot, but it will still work fine IMO. A 12 Volt PS would deliver 11.94V to the charger at 30 Amps.

I think most people would want to use 14 or 12 gauge wire for the output of a 30 Amp supply just to minimise voltage losses and have no heating. I would, but honestly your setup is just fine if you run it and it doesn't get warm enough to bother you.

John

Quote:
 Originally Posted by stgdz So i have less than 2 inches of 18 gage wire from my posts to jacks. Can that handle 30amps for 8 minutes? Standard is rated to 15 but not sure on run length.
Last edited by jj604; Jun 19, 2012 at 05:55 PM.
Jun 19, 2012, 09:10 PM
Registered User
Joined Apr 2012
4 Posts
Quote:
 Originally Posted by xandrios Hey jay4. If you have a 10 turn pot you can turn any multimeter with a 2000µA setting into a universal current measuring device that can read up to 2000A.

for now I'm just using OLD VU meter with home made shunt resistor.. but it not satisfied me.. i think the measurement current not accurate.. maybe any one can explain how to calibrate this type of meter..
 Jun 20, 2012, 08:26 AM Volts>amps United States, MN, Buffalo Joined Jul 2011 4,028 Posts Thanks guys, I lm going to run this setup very little as its the cabin charger. Don't have any 12 gage wire around.
Jun 20, 2012, 10:28 AM
Steven
United States, CT, East Hartford
Joined May 2010
504 Posts
Turn any DVM with a 2000µA range into a universal DIY 2000 Amp DC Ammeter.

Discussion found here

Turn any DVM with a 2000µA range into a universal DC Ammeter that can read up to 2000 Amps.
Can be used with or without a Manganin Current Shunt.
Can be used with or without a potentiometer.
A value of 1 on the meter will equal 1 amp of current.
Use one of the three methods.

METHOD 1 - Without Potentiometer - high accuracy

This method is best for high current measurement and high accuracy

Set multimeter to 2000µA range.
Connect DVM leads directly to Current Shunt attachment points or connect to wire/cable at the specified length below.
Adjust by moving leads closer or farther apart along the wire/cable and calibrate against a known amount of high current for best results.
An X number of wires/cables used in parallel needs X times the length.

The specified lengths of wire/cable should have a voltage drop of 0.1mV per amp.
1.2" 10 gauge copper wire. Hard to adjust. Suggest to use method 3.
1.91" 8 gauge copper wire. Hard to adjust. Suggest to use method 3.
3.04" 6 gauge copper wire. May be hard to adjust. Or use method 3.
4.83" 4 gauge copper wire. 134 amps continuous. 270 amps peak. Great DIY Current Shunt.
7.68" 2 gauge copper wire. 181 amps continuous. 360 amps peak. Great DIY Current Shunt.
9.69" 1 gauge copper wire. 211 amps continuous. 420 amps peak. Great DIY Current Shunt.
12.21" 0 gauge copper wire. 245 Amps continuous. 500 Amps peak. Great DIY Current Shunt.

Works directly with any Current shunt with a 0.1mV drop per Amp and requires no calibration.
500A 50mV Shunt --- 750A 75mV Shunt --- 1000A 100mV Shunt --- 2000A 200mV Shunt
For continuous operation, it is recommended that shunts are not run at more than two-thirds (2/3) the rated current under normal conditions.

Accuracy variables include: The temperature coefficient of resistance of the shunt material.
This value for Copper is 0.2183% per degree Fahrenheit.
If calibrated at 70 degrees then the meter will have an error of 2.2% at 60 degrees and 80 degrees. R(T) = R(T0) * [ 1 + a(T - T0) ].
A thicker wire/cable will heat up less when passing a high current and will be more accurate with high loads.
A Manganin Current Shunt has a temperature coefficient of resistance that is very close to zero.

METHOD 2 - With Potentiometer and with Current Shunt - high accuracy

This method will solve most incompatibility issues when using Current Shunts with a multimeter

Set multimeter to 2000µA range.
A 10 or 15 turn potentiometer (100Ω - 1kΩ) will be needed.
Use the pot as a variable resistor and connect in series with one of the DVM leads.
Connect to the Current Shunt attachment points.
Adjust with pot and calibrate against a known amount of high current for best results.
The meter will scale correctly for any value after adjustments are made.

Follow these rules for Current shunts:
Will work with any 20A, 50A, 75A, 100A, 200A, 300A and 400A shunt.
Will work with any Current Shunt that has more than a 0.1mV drop per Amp.
If the voltage drop is equal to 0.1mV per amp then the pot is not needed.
If the voltage drop is greater than or equal to 1mV per amp then use the 200µA or 200mv setting.

Examples:
200A 75mV shunt = 75/200 = 0.375mV/amp = will work --- 500A 75mv shunt = 75/500 = 0.15mV/amp = will work.
700A 100mv shunt = 100/700 = 0.143mV/amp = will work --- 500A 50mv shunt = 50/500 = 0.1mV/amp = pot not needed.
1000A 75mv shunt = 75/1000 = 0.075mv/amp = will not work --- 2000A 200mv Shunt = 200/2000 = 0.1mV/amp = pot not needed.

Equation for approximating the pot resistance for a particular Current Shunt to within ±5% of a fully calibrated system:
Pot resistance ≈ (millivolts/amps - 0.1) x 1100.

Examples:
100A 75mV shunt = (75/100 - 0.1) x 1100 = 0.65 x 1100 = 715 Ω
250A 75mV shunt = (75/250 - 0.1) x 1100 = 0.20 x 1100 = 220 Ω
500A 75mV shunt = (75/500 - 0.1) x 1100 = 0.05 x 1100 = 55 Ω
500A 50mV shunt = (50/500 - 0.1) x 1100 = 0 x 1100 = 0 Ω = no pot needed
1000A 75mv shunt = (75/1000 - 0.1) x 1100 = -0.025 x 1100 = negative value = will not work

Accuracy variables include: The temperature coefficient of resistance of the potentiometer.
Large variations in ambient temperature may affect the resistance value of the pot.

METHOD 3 - With Potentiometer and without Current Shunt - moderate to high accuracy

This method is best for easy adjustment/calibration when only using wire/cable

Set multimeter to 2000µA range.
A 10 or 15 turn potentiometer (100Ω - 5kΩ) will be needed.
Use the pot as a variable resistor and connect in series with one of the DVM leads.
Then connect to two points on the wire/cable.
Adjust with pot and calibrate against a known amount of high current for best results.
If for any reason you can't get the multimeter to match the actual current draw then simply move the connection points
further apart on the wire/cable and adjust again.
The meter will scale correctly for any value after adjustments are made.

Follow these rules for copper wire:
10 gauge to 22 AWG connect leads more than 1.2"(inches) apart. Recommend for use.
8 gauge connect more than 1.91" apart. Recommend for use.
6 gauge connect more than 3.04" apart. Or use method 1.
4 gauge connect more than 4.83" apart. Or use method 1.
2 gauge connect more than 7.68" apart. Or use method 1.
1 gauge connect more than 9.69" apart. Or use method 1.
If your wire/cable is 10 times or greater than the length suggested in method 1 then use the 200µA or 200mv setting.

Equation for approximating the pot resistance for a particular copper wire/cable:
Pot resistance ≈ (actual length being used /length from method 1 - 1) x 110

Examples:
(6" of 10 gauge wire / 1.2" for 10 gauge - 1) x 110 = (6/1.2 - 1) x 110 = 4 x 110 = 440 Ω
(4" of 8 gauge wire / 1.91" for 8 gauge - 1) x 110 = (4/1.91 - 1) x 110 = 1.09 x 110 = 120 Ω
(6" of 6 gauge wire / 3.04" for 6 gauge - 1) x 110 = (6/3.04 - 1) x 110 = 0.97 x 110 = 107 Ω
(4.83" of 4 gauge wire / 4.83" for 4 gauge - 1) x 110 = (4.83/4.83 - 1) x 110 = 0 x 110 = 0 Ω = no pot needed
(6" of 2 gauge wire / 7.68" for 2 gauge - 1) x 110 = (6/7.68 - 1) x 110 = -0.219 x 110 = negative value = will not work

Accuracy variables include: The temperature coefficient of resistance of copper and the potentiometer.
Large variations in ambient temperature may/will affect the resistance values.
A thicker wire/cable will heat up less when passing a high current and will be more accurate with high loads.

# Images

Last edited by xandrios; Sep 30, 2012 at 02:51 PM.
 Jun 20, 2012, 09:24 PM Registered User Joined Apr 2012 4 Posts thank you xandrios.. it's really work..
 Jun 23, 2012, 03:02 AM Registered User Joined Jun 2012 5 Posts How do those power supplies behave in over current mode ? Any ideas if they go into hiccup or constant current mode ? Would like to use them as battery chargers directly (DPS-500 CB-A or DPS-700 EB possibly ?) Thanks
 Jun 24, 2012, 01:36 PM Registered User Joined Jun 2012 14 Posts My DL580 (40621-001) has had the fan mod done to it (2w-10ohm resistors) and I'm having a slight "issue". I don't know if it's because of the mod or not, but it faults if I unplug one of my chargers. Pins 6-8-10 are connected, and I usually plug the chargers in before plugging the supply into the wall. Starts and runs fine, but I wanted to see what firmware was loaded on my 206b's so I unplugged one and a few seconds later the other one shuts off, the fans slow on the PS and I get an amber light. I have to pull the plug, wait for the supply to shut off, then plug it back in. I haven't tried it while the other charger is charging, but it does it when discharging to storage mode. Is this an expected fault, even if the fans hadn't been modded?
 Jun 24, 2012, 02:45 PM Steven United States, CT, East Hartford Joined May 2010 504 Posts I think that connecting Pins 6-8-10 together are meant for the DPS-600PB PSU. Connecting pin C4 to the +12v output and connecting pin C5 to ground should help for your DL580G3 PSU.
Jun 24, 2012, 03:21 PM
Registered User
Joined Jun 2012
5 Posts
Quote:
 Originally Posted by mige0 How do those power supplies behave in over current mode ? Any ideas if they go into hiccup or constant current mode ? Would like to use them as battery chargers directly (DPS-500 CB-A or DPS-700 EB possibly ?) Thanks
got my questions - partly - answered here:

Jun 24, 2012, 06:23 PM
Registered User
Joined Jun 2012
14 Posts
Quote:
 Originally Posted by xandrios I think that connecting Pins 6-8-10 together are meant for the DPS-600PB PSU. Connecting pin C4 to the +12v output and connecting pin C5 to ground should help for your DL580G3 PSU.
Brain fart on my part, sorry. Yes, my 600PB is set up that way. The 580 has pins B2,3&4 connected together.
Looking at post #495, C4&5 are remote sense connections. Will hooking those up to the 12v rail keep the PS alive if I unplug one of the chargers? Am I just fooling it into thinking there's another supply connected?
It's really not a huge deal, as the only reason I unplugged one of the chargers was to see it boot and see what firmware was loaded. I suppose there are cases where I will need to do it while the other is charging, like if it's locked up or something.
 Jun 24, 2012, 06:31 PM Steven United States, CT, East Hartford Joined May 2010 504 Posts Connecting up the sense pins usually gives a PSU a better idea of whats going on with load conditions.
 Jun 24, 2012, 06:37 PM Registered User Joined Jun 2012 14 Posts Thanks. I'll give it a go. BTW: I grew up in CT. Spent the 1st 10 years of my life as a Navy Brat, living in Ledyard/Gales Ferry. EDIT: Well, it kinda works. C4 to 12v +ve, C5 to 12v -ve. It stayed on when I unplugged one of the chargers, but faulted when I plugged it back in. EDIT2: It faults if I start with one charger and try to add another even without the RS pins connected. Last edited by Jeckler; Jun 24, 2012 at 06:46 PM.
Jun 25, 2012, 07:40 AM
Steven
United States, CT, East Hartford
Joined May 2010
504 Posts
Next would be to connect a diode in parallel with output to prevent reverse voltage. The diode should be rated to at least the power supply rated output voltage and output current.