Isssues with power supply

sagor

Joined Mar 10, 2019
908
If your source can only provide 2A, then you cannot draw more than that. That current draw depends on the fans, whatever their current draw is. Their startup current will be more than their running current. Many of those laptop chargers do not have a large "surge" current capacity, their voltage will drop if drawing more than designed current.
That all said, the diagram I posted would control "up to" 4A. It does not mean it will draw that much, only what the load requires. That diagram will easily provide 2A, or more if you have a higher capacity power source.
 

Thread Starter

ConstructionK88

Joined Jul 25, 2018
282
If your source can only provide 2A, then you cannot draw more than that. That current draw depends on the fans, whatever their current draw is. Their startup current will be more than their running current. Many of those laptop chargers do not have a large "surge" current capacity, their voltage will drop if drawing more than designed current.
That all said, the diagram I posted would control "up to" 4A. It does not mean it will draw that much, only what the load requires. That diagram will easily provide 2A, or more if you have a higher capacity power source.
Thank you very much for telling me that. I've seen the schematic before but I thought it meant it was FOR controlling 4 amps not UP to 4 amps. My oversight. Though from observation these dc motors seem to prefer voltage over amperage. A 5v 1.5a is much less powerful than a 9v 250ma. The adapter I'm using has nothing to do with its amps. It's simply the highest voltage I have under 48
 

michael8

Joined Jan 11, 2015
414
You can't expect LM317s in parallel to work without some help.

Any two random LM317s are not identical so they have different reference
voltages (spec is 1.2V to 1.4V). Their current and thermal limits
are likely different as well as the change in their reference voltages
with temperature.

The one with the highest reference voltage supplies all the current it
can to it's current limit, the other supplies the rest.

The first is handling most of the current so after a bit it heats up
more than the other. This changes it's reference voltage even if it
doesn't enter thermal limiting. This might move the load to the other
LM317 which then heats it up.

Depending on the specific LM317s and the load current you might get
different effects, it might even be stable at one specific current and/or
room temperature (or proper phase of the moon).

To have a reliable regulator with parallel LM317s you need a circuit
which forces them to share the current even though they have different
reference voltages.
 

dendad

Joined Feb 20, 2016
4,471
Slow turn on is the problem I'm having now. Unfortunately it needs to be quickly adjustable even from on to off and vice-versa.
You are confusing a few things here.
The fans at the moment are slow to turn on as there is not enough current capability to start them at the full voltage.
BUT, if you ramp the voltage up slower, as your earlier post pointed out, the fans will start.
So, the circuit posted in #39 will ramp the voltage up for you so the fans can start up with lower current and then get to the running speed that your power supply can cope with.
 

Thread Starter

ConstructionK88

Joined Jul 25, 2018
282
You can't expect LM317s in parallel to work without some help.

Any two random LM317s are not identical so they have different reference
voltages (spec is 1.2V to 1.4V). Their current and thermal limits
are likely different as well as the change in their reference voltages
with temperature.

The one with the highest reference voltage supplies all the current it
can to it's current limit, the other supplies the rest.

The first is handling most of the current so after a bit it heats up
more than the other. This changes it's reference voltage even if it
doesn't enter thermal limiting. This might move the load to the other
LM317 which then heats it up.

Depending on the specific LM317s and the load current you might get
different effects, it might even be stable at one specific current and/or
room temperature (or proper phase of the moon).

To have a reliable regulator with parallel LM317s you need a circuit
which forces them to share the current even though they have different
reference voltages.
Thanks for input. Output resistors are shown in several diagrams with parallel ICs. These are thier purpose? I must have just gotten lucky all those times before
 

djsfantasi

Joined Apr 11, 2010
9,160
My apologies I was referring to the power at which the fans blow. Even with low amperage the voltage seems to influence them the most
The power of the fans subjectively will be related to the calculated electrical power. So the two posts are referring to the same thing.

Voltage changes will affect electrical power changes. So while on the surface it appears to be voltage related, it’s not.
 

Thread Starter

ConstructionK88

Joined Jul 25, 2018
282
I appreciate all the help. I believe I narrowed it down to one of the motors being a different design. The 2 that work perfectly are the same model while the other is a beefier design. Guessing it demands more power than the other 2. Either 2 work together but that one is a tad slower to get to speed. It makes more sense why it worked before but not now. most look identical and I likely had a mix up. The ICs are certainly lower quality than the ones I had previously but they work well enough for now.
 

crutschow

Joined Mar 14, 2008
34,403
I thought the draw or amperage would always be the same since the lm317s simply control the voltage given the circuit I'm using?
Yes, they control the voltage, but the current is determined by the motor fan load which increases when the fans are accelerating.
The fan motors do not draw a constant current when they are changing speed.

Motors are not a fixed current load, which you seem to think.
Their current, at a fixed voltage, can easily vary over a 10:1 range, depending upon load.
 
Last edited:

shortbus

Joined Sep 30, 2009
10,045
. @shortbus you sir, with respect, are excellent with electronics but stay away from construction with your mickey mouse paint tactics.
Oh? Your not the same ConstructionK88 from over at ETO? The one using the same avatar? The one who actually said something on the order of what I said about you? That treated lumber wasn't necessary to build a deck. Maybe I paraphrased a little, but the gist of it is the same. The same guy who proposed heating his house with the exhaust heat from his forge?
 
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