[NSRCA-discussion] regulators

[Ed Alt]

Bob:
The regulator is probably doing just fine. Every regulator that's out there 
for use in our models has one thing in common.  They regulate the voltage 
output at the point that the regulator is physically connected to.  They 
can't "see" the actual voltage at the end of the wires where your servos 
are. They can only see it at the point where the pins leave the regulator IC 
package.  What is happening is that a voltage drop is developing across all 
of the wiring in between the regulator and the load where you are measuring. 
The voltage drop is calculated by E=IR, where voltage is E, current is I and 
R is resistance.

There are two ways to accomplish regulation at the load.  One is to have a 
remote sense design to the voltage regulator system, which actually takes 
the true voltage at the point where the load connects and feeds that back to 
the regulator, to permit the regulator to compensate for the losses in the 
wiring. In practice, this would not work for our application, since the load 
varies at each servo, so if servo 1 is drawing a bunch of current and thus 
experiencing a lower voltage, the other servos actually don't see a voltage 
as low as the one drawing the load. So if you boosted the regulator voltage 
to make servo #1 happy, the others would see a higher voltage.  The end 
result is that the voltage would be all over the place on the high side, 
which is not desireable.

The other thing you could do is just place a regulator at each servo.  Jim 
Oddino could tell you more about it, since he has this setup flying, but 
it's a perfectly good method if you don't mind doing the wiring up at the 
end of each extension. It has several benefits, some minor drawbacks, 
overall it's a cool idea.  Believe it or not, even though you are seeing 
this effect of wiring resistance, you are still better off with the one 
regulator that you have.  It is taking away the effect of the battery's 
internal resistance and all of the wiring in between it and the battery, so 
the servos are in fact getting a more constant supply than they otherwise 
would.

Ed

----- Original Message -----
From: "Robert Mairs" <robertm at sssnet.com>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Wednesday, December 06, 2006 7:53 AM
Subject: [NSRCA-discussion] regulators

> I've got a Jaico that regulates to 6.11 volts.   Using a 480 mah TP lipo,
> and the Jaico, I got the following.
>
> no load, 6.11v
> 500mah load, 5.72v
> 1A load, 5.63v
> 1.5A load, 5.54v
>
> Just with the battery, no regulator I get
>
> no load, 8.2v
> 500mah, 7.84v
> 1A, 7.51v
> 1.5A, 7.2v
>
> I don't understand.  Why doesn't the regulated voltage stay at 6.11v with 
> a
> load?  I always thought using a regulator was supposed to give you a
> constant voltage so the servos reaction would always be the same, yet it
> acts just like a battery,  just not as great a drop off it seems.
>
>
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