Victor Tikhonov wrote:
> Browsing for something else, I found this site:
>
> http://www.skiebus.com/bms.htm
>
> They make something similar to powercheqs but instrad of
> DC-DC or flying capacitor they use flying inductor which
> stores the energy being shuffled around.
>
> On their site it's shown as symmetrical bi-directional device,
> which is not the case for trivial DC-DC.
The circuit they show is the standard buck-boost converter found in any
textbook. The diode-plus-switch they show is just a MOSFET. I don't see
how they got it patented unless the examiner was hung over, or they
claimed some trivial enhancement.
Jon "Sheer" Pullen wrote:
>> Me & Lee discussed a small mod to the mk3s that would let them
>> perform this operation across a entire string; similar technique.
For those that want to play, here it is. Assume two Rudman MK1 or MK2
regulators on two batteries. You also need a 60 Hz impedance-limited
"class 2" transformer with two 24v windings (or two identical
transformers; I used a pair of 120vac-to-24vac 10va doorbell
transformers with their primaries connected together). Wire like this
(view with fixed width font):
________________ _________________
+12v___|________________|____0 ____|_________________|______+12v
| Rudman | _| || |_ | Rudman |
| Regulator #1 | _| || |_ | Regulator #2 |
Battery| _____|____| || |____|______ | Battery
#1 | |_| _|_ | 0 | _|_ |_| | #2
| MOSFET |_ /_\ | 24v/24vac | /_\ _| MOSFET |
| | | | | 60Hz Class2 | | | | |
-12v___|__________|__| | transformer | |___|__________|______-12v
|________________| |_________________|
Disconnect the Rudman Regulator's on-board resistor. Connect the 24vac
transformer secondary as your external "load" resistor. A class 2
transformer winding has several ohms of DC resistance; it will get hot,
but won't burn up if the Regulator ever latches fully on.
Note the phasing dots "0"; the two transformer secondaries are connected
OPPOSITE from each other -- this is important.
How it works: Suppose battery #1 reaches "full" first. Regulator #1
turns its MOSFET on. Current flows thru the left transformer winding
(phasing dots positive) and current ramps up. This loads battery #1,
pulling its voltage down, so the regulator turns off. The inductive
energy stored in the left winding makes the voltage across each winding
reverse (phasing dots negative). There is no path on the left side, but
on the right side, this makes the MOSFET's body diode conduct. The
inductive energy is therefore dumped into battery #2, charging it.
The reverse is true if battery #2 is higher in voltage. Instead of
burning up the energy in resistors, this circuit dumps it into the other
battery!
You need the impedance-limited transformers because nothing prevents
Rudman Regulators from latching full "on". A high quality efficient
transformer would saturate, and place nearly a dead short across the
battery, and the MOSFET would fry. The class 2 transformer is an easy
way around this without any modifications to the regulators.
If you DO happen to use two 120vac-to-24vac transformers, what happens
if you plug these primaries into the AC line? You have individual
battery chargers for equalization! The transformer secondary and MOSFET
body diode form a simple transformer-rectifier charger. Battery voltage
is limited by the regulator as usual, and charging current is limited by
the class-2 transformer's impedance.
One tip if you use this scheme for charging; put an AC-rated capacitor
in series with the transformer primaries before connecting them to the
AC line. If a regulator latches fully on while you are charging, the
transformer will overheat because it is delivering its full current into
what it sees as a shorted load *and* the battery is supplying additional
current into the secondary. A series capacitor in the primary limits the
primary current, and thus keeps the transformer from overheating.
This is a real dumb-and-dirty circuit. It works, but BIG improvements
can be made if one is willing to modify or redesign the MK1 or MK2
regulators.
--
Lee A. Hart Ring the bells that still can ring
814 8th Ave. N. Forget your perfect offering
Sartell, MN 56377 USA There is a crack in everything
leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen
