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BFL13's avatar
BFL13
Explorer II
Nov 04, 2014

Buck Gizmo Test Results

This test was to see how much the amps went up at the output of the buck converter compared with the input amps. This is the gizmo again:

http://www.ebay.com/itm/DC-DC-15A-Converter-Buck-Adjustable-4-32V-12V-to-1-2-32V-3-3V-5V-24V-Step-Down/281206555382?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25217%26meid%3D8539ba1eede94f48b9c4da74610ac108%26pid%3D100011%26prg%3D10629%26rk%3D5%26rkt%3D10%26sd%3D351129151726&tfrom=351129151726&tpos=unknow&ttype=price&talgo=origal

So first I attached four pigtail thin wires to the terminals set screw type and then attached fatter wires to those and got all set up.

I put my two, 2a float chargers in series and tested the output at the "working" clamps at 27.0v

No load bench test of adjustable voltage CV screw pot. With 27v in, and meter on output, set it to 14.8v The little screw turns many times and you can set voltage exactly all the way through its range. In this case I stopped at 26v output in case I would fry something hitting the input voltage, no idea, but I had not even started the test yet so that would be annoying to fry it now. ok

Next test is with no input, connect to battery bank. The input voltage was the same as the battery voltage on the output, 13.82v, then with converter off, voltage down, 12.81

So it just passed through the voltage going that way from out to in across the circuit board.

So now the biggie, with battery connected 12.8v, connected input 27v with ammeter in the pos input line showing amps bouncing around between 1.55ish to 1.75ish----------so what were the output amps????

The same!!! Rats, phooey. Ok , maybe the batts won't accept any more, try it with a load. On Trimetric without the buck converter on, got 12.3v and -20.3a. Turn on gizmo, 12.3v and -18.3 so 2a from gizmo. Tried a few more like that pretty much the same results

Maybe a slight hint of higher amps? Hard to tell with these small amounts and rough instruments but it sure didn't double the amps like I expected.

OK final desperate test using an actual 230w solar panel as input.

Dull day so panel de-rated already so ok for input to gizmo at
Voc 31.0 Isc 0.3a Batts now 12.8, no solar Tri shows -0.3 to -0.4 back and forth as normal with converter off. Add solar power to gizmo, amps on Tri now 000 to +0.1
So same as panel Isc for gizmo output or maybe a titch more , hard to say.

RATS!!!

So what went wrong? Should amps have been more at the output or not?
Thanks.

18 Replies

  • You are neglecting the fact that solar panels are current sources. When in boost mode, the controller shorts the panel to the battery. The charging current is Isc.

    In absorption mode, charging current must be less than Isc. If the controller can't maintain regulation (the load + charging current > Isc) then the controller will revert to boost mode.

    In your case, if you set the regulator 14.2V and the battery is at 13.0V then the converter is not in regulation. It's doing things it's not designed for. The inductor may go into saturation. Now there's virtually no current limit and the series pass transistor could get destroyed.
  • I don't have it set up anymore to try that, but that procedure is not any good for my purpose anyway. I thought it would work like a solar controller does in PWM.

    How can a solar controller, which is a buck converter (AFAIK) do this and my gizmo can't? The gizmo bucked the voltage ok but just passes through the same amps. Similar to a PWM controller on a 12v panel that bucks from 21v to Vbatt but passes panel Isc through as amps EG you get the 8.2 amps from the 130w panel going to the battery.

    In this case, "panel" voltage was 27v and 2 amps and output was 2 amps at Vbatt. So it was like the buck converter for a 12v panel except with higher intake voltage but not like the one for a 24v panel

    With the solar controller for a 24v panel which also has Isc of 8.2 amps, you get more amps than the panel's Isc, almost twice the amps. EG my 230w with the controller gets say 15 amps to the battery.

    You just set the Vabs on the controller and let her rip. No need to keep the high set point just above the battery's voltage to get your jump in amps.

    What is in or with the solar controller's buck converter for a 24v panel to let it double the amps going from 24 to 12v that my gizmo rated for up to 32v intake doesn't seem to have?
  • This regulator is only capable of supplying 10A, but your battery wants more. The regulator goes out of regulation. That's why I sad to lower regulator voltage to just above Vbat. Now you should be able to increase Vreg and watch current increase. I don't think there's much voltage overhead.

    Icharge = Vreg - Vbat / charging cable resistance

    You need to keep Icharge under 10A.
  • Salvo wrote:
    I believe you regulator is operating in discontinuous mode. Simple mathematics do not apply. Change the regulator voltage to a hair above Vbat.


    Ok I memorized this, :(

    http://en.wikipedia.org/wiki/Buck_converter

    I don't see the value in keeping on adjusting the CV to stay just ahead of rising battery voltage if that is what it takes to get the amps. I want that CV setting to be Vabs and until Vbat gets to Vabs, for the thing to be in Bulk.
  • I believe you regulator is operating in discontinuous mode. Simple mathematics do not apply. Change the regulator voltage to a hair above Vbat.
  • jrnymn7 wrote:
    When the full batts wouldn't accept anymore amps, what load did you apply?


    20amps worth of lights and fans (mentioned above where that went to 18 showing a 2a input.

    the gizmo output was set at 14.8v but the voltage at the output terminals was same as battery when all going of course. The output voltage was way less than the input voltage. Input amps measured correctly as 2a ( two 2a chargers in series) So I suppose input watts was 27 x 2 = 54w If output watts was also 54 and voltage 13 (say) then I should have seen 4 amps out instead of 2. I thought. Nope.