Fusible Link Wire for Voltmeter

[The Dougster]

Hello, sci.electronics.design readers.

I have been working on an "electric flywheel bicycle" for five years
now. In various versions, a road-wheel or crank-coupled brushed DC
electric motor/generator is always coupled to an ultracapacitor pack.
Energy stored is proportional to voltage squared, and voltage a linear
function of speed, so it acts like a massive flywheel with fluid
clutch.

I have 6 Maxwell Technologies manufacture PC 2500 model 2700 F, 2.5
WVDC rated ultracapacitors on the current bike, which can source 4500
amps into a short. I'd like to fuse the voltmeter with fusible link
wire. The last time I had a voltmeter short I was using 24 gage solid
wire and it didn't open. It smoked the nylon fabric capacitor pack. I'd
like to avoid damage to the surrounding equipment.

Where do I get flat cable, 24 conductors, that will fuse and part on a
short? Would ribbon cable for computer equipment do the job?

I don't want to just fuse the return wire; I will be metering 12 caps
soon to establish the standard deviation of voltage and so the
capacitance distribution, with an eye to avoiding cell overcharge by an
appropriate pack charge limit. A DMM with serial comm gets the measured
values into a spreadsheet to do the standard deviation.

I have some 12-contact rotary switches to monitor cell or pack
voltages. One will be wired to 12 negative terminals, one to 12
positive terminals, and a mis-switch would short a cell. Right now
that's the way to do it. In the future, an NI.com USB DAQ with auto
range will monitor 12 voltages above ground with no short potential.
The onboard voltmeter is a 15 V analog panel meter with 50 mv internal
full scale capacity. Two bannana/probe jacks interface the DMM when
balancing is undertaken.

The 12 caps will be in two banks of 6, series within packs,
series/parallel pack by pack, to give regeneration (parallel) and boost
(series) modes of propulsion. Power is also taken out by an inverter,
but when the packs are in parallel, this imbalance is rebalanced..

It's not a problem to replace all the wires right now if one opens
under a short.

There is a 100 ohm, 1/4 watt resistor across each cell to establish and
maintain balance by voltage division. I will go to 1/2 watt soon for
more durable lead wires.

When the characteristics of the cells are known, the whole tap system
will be pulled and replced with clip leads for use only when parked.


Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394

 

[Robert Baer]

Hello, sci.electronics.design readers.

I have been working on an "electric flywheel bicycle" for five years
now. In various versions, a road-wheel or crank-coupled brushed DC
electric motor/generator is always coupled to an ultracapacitor pack.
Energy stored is proportional to voltage squared, and voltage a linear
function of speed, so it acts like a massive flywheel with fluid
clutch.

I have 6 Maxwell Technologies manufacture PC 2500 model 2700 F, 2.5
WVDC rated ultracapacitors on the current bike, which can source 4500
amps into a short. I'd like to fuse the voltmeter with fusible link
wire. The last time I had a voltmeter short I was using 24 gage solid
wire and it didn't open. It smoked the nylon fabric capacitor pack. I'd
like to avoid damage to the surrounding equipment.

Where do I get flat cable, 24 conductors, that will fuse and part on a
short? Would ribbon cable for computer equipment do the job?

** I srongly suggest to use actual fuses!

I don't want to just fuse the return wire; I will be metering 12 caps
soon to establish the standard deviation of voltage and so the
capacitance distribution, with an eye to avoiding cell overcharge by an
appropriate pack charge limit. A DMM with serial comm gets the measured
values into a spreadsheet to do the standard deviation.

I have some 12-contact rotary switches to monitor cell or pack
voltages. One will be wired to 12 negative terminals, one to 12
positive terminals, and a mis-switch would short a cell. Right now
that's the way to do it. In the future, an NI.com USB DAQ with auto
range will monitor 12 voltages above ground with no short potential.
The onboard voltmeter is a 15 V analog panel meter with 50 mv internal
full scale capacity. Two bannana/probe jacks interface the DMM when
balancing is undertaken.

** If the cells are used in parallel, the switching scheme you seem to
imply is rather excessive and not necessary. Use a busbar on the (say)
negative side whith monitoring and balancing circuitry on the seperate
positive terminals.
OTH if they are in series, why use seperate switches which obviously
asks for trouble; ganged multi-wafer switches are easily obtainable.

The 12 caps will be in two banks of 6, series within packs,
series/parallel pack by pack, to give regeneration (parallel) and boost
(series) modes of propulsion. Power is also taken out by an inverter,
but when the packs are in parallel, this imbalance is rebalanced..

It's not a problem to replace all the wires right now if one opens
under a short.

There is a 100 ohm, 1/4 watt resistor across each cell to establish and
maintain balance by voltage division. I will go to 1/2 watt soon for
more durable lead wires.

** Why do you continuously *waste* power when that is not necessary?

 

[The Dougster]

** I srongly suggest to use actual fuses!

Yes, and I think this is the best policy.

** If the cells are used in parallel, the switching scheme you seem to
imply is rather excessive and not necessary. Use a busbar on the (say)
negative side whith monitoring and balancing circuitry on the seperate
positive terminals.
OTH if they are in series, why use seperate switches which obviously
asks for trouble; ganged multi-wafer switches are easily obtainable.

I just had a little trouble finding the 2-gang 12-position non-shorting
switch. I will find one soon.
They are in a 6-cell series bank now. Two banks of 6 in series will be
switched series/parallel soon. See below for an alternative.

** Why do you continuously *waste* power when that is not necessary?

I do this because Maxwell recommends it at the minimum. What I really
want is a generalized solution to putting N ultracpacitors in
series/parallel all they way from N series for maximum voltage to N
parallel for maximum capacitance, including all JxK configurations
where J and K are complementary divisors of N.

What I have towards that goal are some 8A rated relays and some boards
I had made but the relayss don't latch. That was the best I could find
at Digi-Key. I am looking for 15 A relays that latch, in a DIP
configuration, with 2.5 V coils. Those are like hen's teeth.

I had 6 boards manufactured by pcbexpress.com. I machined the vent cap
holes in the boards to 17mm and the supplied plated holes to 6mm for
the capacitor terminals with a drill press and reamer. I have not sawed
the 2-up boards apart. I still have the design saved. Each board mounts
to a capacitor to allow the 2x3 configuration for the rack trunk and
the 1x6 configuration for the seat bag.

I had designed a 4x2 relay PCB in Windows Paint but never made it up. I
sent it to a local shop for vinyl masking but they flubbed it. Also, as
a small producer of waste, I might pollute more than necessary with a
small job, where a large company would probably deal with waste in
volume, under regulation, and efficiently. So I gave up on making a
board myself.

A local design shop offerd to build a board with MOSFET balancing and
series-parallel switching for thousands of $$$$. No way was I ready to
do that; I am not doing that kind of volume. That is for much later.

I believe the way I designed the boards they can do JxK switching,
although I only intended 1xN and Nx1 configurations at the time. It has
a lot to do with reducing the many abitrary and equivalent JxK
arrangments to just one. There is only one 1xN and one Nx1
confiuration, barring permutations.

Doug

 

[Robert Baer]

----------- SNIPped --------

I do this because Maxwell recommends it at the minimum. What I really
want is a generalized solution to putting N ultracpacitors in
series/parallel all they way from N series for maximum voltage to N
parallel for maximum capacitance, including all JxK configurations
where J and K are complementary divisors of N.

What I have towards that goal are some 8A rated relays and some boards
I had made but the relayss don't latch. That was the best I could find
at Digi-Key. I am looking for 15 A relays that latch, in a DIP
configuration, with 2.5 V coils. Those are like hen's teeth.

** High current handling relays are not made in DIP configuration,
mainly because the relatively tiny pins cannot handle that current reliably.
Try "automotive" style relays; the F-tabs could plug into connectors;
alternately use the tabbed relays or octal relays and their sockets.
I assume you want to use sockets for replaceability.
A relay with an extra set of contacts can be made to latch.
A 5V relay can be altered for reliable (but relatively slow due to
lower amp-turns) pullin by weakening the spring.
Adding a magnet can speed it up and make it a latching relay, but you
may need to add some thin paper or mylar tape at the solenoid pole to
prevent the armature from sticking.

 

[James Waldby]

....

Several people mentioned that voltmeters have high-impedance inputs,
so some series resistance is ok. Ie, you would have voltage sensing
leads separate from the high-current leads. Each voltage sensing
lead could have a 10K (eg) resistor at its capacitor, after which it
would not need a fuse. The high-current leads might need fuses, but
that apparently won't involve your rotary switches.

....

I had designed a 4x2 relay PCB in Windows Paint but never made it up. I
sent it to a local shop for vinyl masking but they flubbed it. Also, as
a small producer of waste, I might pollute more than necessary with a
small job, where a large company would probably deal with waste in
volume, under regulation, and efficiently. So I gave up on making a
board myself.

One can make small boards with negligible waste of chemicals ~
just time ~ eg see http://pat7.com/jp/etch/ .

-jiw

 

[The Dougster]

...

Several people mentioned that voltmeters have high-impedance inputs,
so some series resistance is ok. Ie, you would have voltage sensing
leads separate from the high-current leads. Each voltage sensing
lead could have a 10K (eg) resistor at its capacitor, after which it
would not need a fuse. The high-current leads might need fuses, but
that apparently won't involve your rotary switches.

Yes, I understand that now.

...

One can make small boards with negligible waste of chemicals ~
just time ~ eg see http://pat7.com/jp/etch/ .

That's how I did my board in Paint; I flooded the traces to avoid waste
of etchant and pollution of copper products. I would go back to it, but
now I realize the bike needs two separate packs, each 1x6 electrically,
but one 3x2 mechanically and the other 1x6. Maybe I will go back to it.

Doug

 

[Rich Grise]

I had designed a 4x2 relay PCB in Windows Paint but never made it up. I
sent it to a local shop for vinyl masking but they flubbed it. Also, as
a small producer of waste, I might pollute more than necessary with a
small job, where a large company would probably deal with waste in
volume, under regulation, and efficiently. So I gave up on making a
board myself.

Don't worry about "waste", if you're talking about etching a copper
PC board.

Use ferric chloride (FeCl3) for the etchant, and when it's used up (i.e.,
so much cupric chloride that it won't etch any more), then pour washing
soda (sodium carbonate - NOT bicarb) into it, and it neutralizes the
chlorides by bonding the Cl with Na, making NaCl, and the iron and carbon
make carbonates, which are essentially dirt. You could throw it in your
garden, or flush it totally harmlessly. But flush well, it _is_ mud, and
will leave sediment.

Cheers!
Rich