Hunter Cook wrote:
> Roland,
>
> As always, thanks for all the info. Not sure I grok all of what you're
> saying, but I think I'm getting most of it. I don't think we're talking
> about quite the same setup...it looks like in this truck there is only
> the one transformer doing what you describe a pair doing in the boost
> circuit. Note that I'm describing the way it came to me wired up (as
> opposed to something I'm considering wiring up). My assumption is that
> he did it this way because he wanted the charge to handle a
> higher-voltage pack. It's just one transformer with a single 120v
> primary and two 20v secondaries. The 120v from the wall comes into a
> terminal strip and goes to both the transformer and the BC-20. Then the
> two primaries are series run to provide 40v to the BC-20 on the boost
> circuit inputs, which are expecting 20v from the LB-20 boost module.
>
> So, in other words, it's getting twice as much from its boost circuit as
> the designers intended, which I assume means it needs a resistor
> different from the one for 120v that the manual specs. I'm not sure what
> it would need to be...all the voltages seem to have resistors about 4-6k
> apart, except the last one (the jump to 120 with the boost unit) is 11k.
> I guess given that it's a 12v increase and the rest are 6, that makes
> sense and the 144v resistor would be about 22k higher, but that's just
> my simple-arithmetic approach to the problem...not any real electrical
> theory going on over here. I'll look inside and find out what resistor
> is actually in there soon.
>
> Meanwhile, if any of you Zivan owners has seen the light in that other
> thread and want to upgrade to one of these fancy Brusa units, let me
> know ;-)
>
> Thanks again Roland.
>
> Hunter
>
>
>
> On Tue, 2007-10-02 at 09:53 -0600, Roland Wiench wrote:
> > Hello Hunter,
> >
> > The series connections in the primaries of several transformers is corrected
> > for connecting to a higher input AC voltage, or increasing the out voltage
> > on the total sum of the windings which will increase the secondary voltage.
> >
> > For example:
> >
> > Lets say you have two transformers that have a 120 volt primary with leads
> > mark L1 and L2 and a 120 volt secondary leads mark T1 and T2. This is
> > normally a 1:1 ratio transformer.
> >
> > The normal way to connect to this transformer is to supply 120 vac to the
> > primaries to each transformer, which parallels the primary leads L1 to L1
> > and L2 to L2.
> >
> > The secondary of each transformer will have a output of 120 volts.
> >
> > Now is we series the primaries of the transformers by connecting one leg of
> > the 240 volt input to L1 and connect L2 of the first transformer to L1 of
> > the second transformer and the second leg of the 240 volt input to L2 of the
> > second transformer, you will still get 120 volts out each transformer
> > secondary.
> >
> > If we connect the secondary of each transformer in series like we did with
> > the primary, you can also get 240 vac out or can get 120/240 volt out if you
> > center tap the secondary series connections that go between the two
> > connections.
> >
> > Another way to connect the 120 vac input power to two transformers that
> > primaries are series together, is to connect 120 volts to the first
> > transformer primary L1 and L2. Connect the first transformer L2 to the
> > second transformer L1 and no connection to the second transformer L2.
> >
> > You can apply the 120 vac power to the primary of the first transformer and
> > using a volt meter, you will read 240 volts between the leads of the L1 of
> > the first transformer and the L2 lead with no connection in the primary of
> > the second transformer.
> >
> > This is what is call a boast circuit or some transformers call a potential
> > transformers which have several taps in the primary.
> >
> > So the series connections you have for the 108 v battery pack should
> > increase for a 120 v battery pack.
> >
> > Also check to see if you have the correct resistor for the 120 v battery
> > pack as listed on page 7 of the manual.
> >
> > Tightening all the wire connections and inspecting the wire for crack
> > insulation and etc, should be ok to fire it up or give it a smoke test.
> >
> > Using Uve's EV calculations, a 120 v battery psck of T-145's should give you
> > a range of 66 miles at 10%D0D, or 33 miles at 50%. A pack of T-105's would
> > be at about 15 miles 50%D)D at a speed of 60 mph with a vehicle weight of
> > 4260 to 4460 lbs.
> >
> > Roland
> >
> >
> > ----- Original Message -----
> > From: "Hunter Cook" <
[email protected]>
> > To: "Electric Vehicle Discussion List" <
[email protected]>
> > Sent: Tuesday, October 02, 2007 8:18 AM
> > Subject: [EVDL] Modified K&W BC-20 questions
> >
> >
> > > Hello again,
> > >
> > > Some of you may recall that I've got an old K&W BC-20 charger trying to
> > > charge a 132v (used to be 144v) pack, which should not (and in my
> > > observation, does not) work very well. Some very knowledgeable folks
> > > have said it's good only to 108v, or 120 with the LB-20 booster. So far
> > > this has all sounded very reasonable, as in my experience the charger
> > > will only bring the pack up to about 140-145v.
> > >
> > > This morning I really got in and looked at the way things were wired up
> > > for the first time. It appears that it is wired with a larger
> > > transformer in an LB-20-style boosting role.
> > >
> > > Specifically, there is a Signal Transformer model MPI-900-40 wired up
> > > exactly the way the BC-20 manual shows an LB-20, except that the MPI is
> > > using 2 20v outputs together in series rather than just the one 20v
> > > output of the LB-20. Here's the pdf of the manual, which has a good
> > > diagram of it: http://evdl.org/docs/bc-20.pdf
> > >
> > > I also found a loose connection from the plug to the MPI. Complete with
> > > burn marks. Awesome. This may be related to the truck flipping the
> > > breaker this morning when I plugged it in, which is what prompted me to
> > > take a more serious look at where the wires were going.
> > >
> > > So...this brings me to a few questions:
> > >
> > > 1. Should this transformer + K&W setup work for a pack of my size? It
> > > seems logical enough I suppose, assuming he also changed out the
> > > internal resistor (haven't had a chance to check, and not sure what the
> > > value should be as the target voltage is higher than the table goes in
> > > the manual) and assuming the other components in the BC-20 can take the
> > > extra voltage. Since the vehicle is pretty old, I guess they can.
> > >
> > > 2. How bad is it that I've got minor burns on my input terminal strip
> > > for the transformer? I tightened up the connection and it works again,
> > > though I didn't try for long.
> > >
> > > 3. Is this dangerous?
> > >
> > > I'm still in the market for a new charger, no doubt about that. But I
> > > hope I can still keep limping around on this one for a minute. I do need
> > > to move the truck about 6 miles this week (from my old house to my new
> > > one) which believe it or not will probably require a charge in the
> > > middle. I'm not really equipped to tow it.
> > >
> > > Thanks again for all the help everybody's been giving me.
> > >
> > > Hunter
> > >
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