An electronidiot's question

Miss_Man · 12-14-2001, 07:01 AM

Without my peltier connected, my power supply gives me 24V as measured by the multimeter. However with my peltier running and the multimeter in the circuit it shows 20V. So is it being given 20V or 24V? Why does the voltage drop when the peltier is added?

resago · 12-14-2001, 08:31 AM

the power supply must not have enough amps to supply the peltier at 24V. so the drain pulls it down to 20V.

20V is a good voltage for a 24v rated pelt, but you run the risk of burning out that underpowered power supply.

[ 12-14-2001: Message edited by: resago ]

Miss_Man · 12-14-2001, 11:12 AM

Then how come when its run at 17V, it drops to 15V when running with the pelt since there is enough amps?

resago · 12-14-2001, 01:59 PM

how many amps is the PS rated?

Miss_Man · 12-14-2001, 02:08 PM

Its actually 2 AT PSUs in series. Rated at 12V 9A each.

GigaFrog · 12-14-2001, 03:07 PM

This is probably because you don't load the 5V output of your PSUs.
To work properly, a AT or ATX PSU needs load on the 5V line.
When you run at 24V, both 12V outputs drop by 2V, leading to a total loss of 4V (20 instead of 24V).
When you run at 17V, you have (I guess thats what you do) a 12V output in series with the other PSU's 5V output. In this case, the other PSU will correctly regulate its 5V, but the first one, runing only its 12V, will still drop by 2V. Total loss = 2V in this case (15 instead of 17).

An advise when you start messing around with PSUs: buy a multimeter, it is cheaper than a PSU, and you will eventually end up spending the money once you will have fried a PSU. The multimeter will help you understand what is goind on, and prevent misusing your PSUs.

Have fun!

Miss_Man · 12-14-2001, 09:44 PM

Actually I do have a load resistor on my 5V. And I use a multimeter to measure. It seems the peltier drops the voltage by 2-3V everytime it runs. Having the multimeter in the circuit won't affect voltage in any way would it?

GigaFrog · 12-14-2001, 10:58 PM

Ooops, sorry for that.
Of course you do have a multimeter, that's how you measured the voltages (how smart ass I was on this one!).

No, the multimeter should not drop the voltages (it's high impedance).
I see two possibillities: you don't load enough the 5V, or you overload the 12V.
At 17V, does the 5V drop?

Hope this helped.

12-14-2001, 07:01 AM	#1
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	An electronidiot's question Without my peltier connected, my power supply gives me 24V as measured by the multimeter. However with my peltier running and the multimeter in the circuit it shows 20V. So is it being given 20V or 24V? Why does the voltage drop when the peltier is added?

12-14-2001, 03:07 PM	#6
GigaFrog Cooling Neophyte Join Date: Nov 2001 Location: NorthWest (French & US) Posts: 88	This is probably because you don't load the 5V output of your PSUs. To work properly, a AT or ATX PSU needs load on the 5V line. When you run at 24V, both 12V outputs drop by 2V, leading to a total loss of 4V (20 instead of 24V). When you run at 17V, you have (I guess thats what you do) a 12V output in series with the other PSU's 5V output. In this case, the other PSU will correctly regulate its 5V, but the first one, runing only its 12V, will still drop by 2V. Total loss = 2V in this case (15 instead of 17). An advise when you start messing around with PSUs: buy a multimeter, it is cheaper than a PSU, and you will eventually end up spending the money once you will have fried a PSU. The multimeter will help you understand what is goind on, and prevent misusing your PSUs. Have fun! __________________ Got water? Water cooled for 3 years. Safe with thermal switch. Now silent with fan thermostat.

12-14-2001, 10:58 PM	#8
GigaFrog Cooling Neophyte Join Date: Nov 2001 Location: NorthWest (French & US) Posts: 88	Ooops, sorry for that. Of course you do have a multimeter, that's how you measured the voltages (how smart ass I was on this one!). No, the multimeter should not drop the voltages (it's high impedance). I see two possibillities: you don't load enough the 5V, or you overload the 12V. At 17V, does the 5V drop? Hope this helped. __________________ Got water? Water cooled for 3 years. Safe with thermal switch. Now silent with fan thermostat.

12-14-2001, 08:31 AM	#2
resago Cooling Savant Join Date: Mar 2001 Location: state of denial Posts: 488	the power supply must not have enough amps to supply the peltier at 24V. so the drain pulls it down to 20V. 20V is a good voltage for a 24v rated pelt, but you run the risk of burning out that underpowered power supply. [ 12-14-2001: Message edited by: resago ]

12-14-2001, 11:12 AM	#3
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Then how come when its run at 17V, it drops to 15V when running with the pelt since there is enough amps?

12-14-2001, 01:59 PM	#4
resago Cooling Savant Join Date: Mar 2001 Location: state of denial Posts: 488	how many amps is the PS rated?

12-14-2001, 02:08 PM	#5
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Its actually 2 AT PSUs in series. Rated at 12V 9A each.

12-14-2001, 09:44 PM	#7
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Actually I do have a load resistor on my 5V. And I use a multimeter to measure. It seems the peltier drops the voltage by 2-3V everytime it runs. Having the multimeter in the circuit won't affect voltage in any way would it?

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