battery pack question

M

Mark Vieselmeyer

Guest
Hello,

I'm building a battery pack for a bike light, and just have a basic question
about what gauge wires & connectors I should use.

What I'm putting together is about 35watts of headlights with 13.2 volts (11
Nimh D cells). I believe that works out to 2.65 amps? Ok, so I'm
connecting the cells by soldering strips of 1/8" copper braid, which
according to one source are approx. 18 awg with a current capacity of 16
amps. So that should be plenty for my setup, correct? I just wanted to
make sure I'm not missing something here, because the braid looks pretty
wimpy. Would there be any advantage to using something thicker?

Also, I'll have about three feet of wire connecting the battery to the
headlights -- any suggestions on what would be the proper guage to use?

Thanks,

- mark
 
You can use a stranded AWG 14 to AWG 16 to be safe. Thicker wire is more
efficient, less loss, and has less chance of any overheating. You are going
to use a lot of current. As for the connectors, you can use the same type
that are on the small trailers. Check with an automotive shop.

There are much more efficient lamps for bicycles. There is now the new solid
state LED types coming out now. You are going to peddling around a lot of
weight in batteries. Also, you won't get more than about 2.5 hours out of
them at full brightness.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Mark Vieselmeyer" <mviesel@hpb15424.boi.hp.com> wrote in message
news:400ed155@usenet01.boi.hp.com...
Hello,

I'm building a battery pack for a bike light, and just have a basic question
about what gauge wires & connectors I should use.

What I'm putting together is about 35watts of headlights with 13.2 volts (11
Nimh D cells). I believe that works out to 2.65 amps? Ok, so I'm
connecting the cells by soldering strips of 1/8" copper braid, which
according to one source are approx. 18 awg with a current capacity of 16
amps. So that should be plenty for my setup, correct? I just wanted to
make sure I'm not missing something here, because the braid looks pretty
wimpy. Would there be any advantage to using something thicker?

Also, I'll have about three feet of wire connecting the battery to the
headlights -- any suggestions on what would be the proper guage to use?

Thanks,

- mark
 
Out of interest how are you planning to charge 11 NiMH cells?


"Mark Vieselmeyer" <mviesel@hpb15424.boi.hp.com> wrote in message
news:400ed155@usenet01.boi.hp.com...
Hello,

I'm building a battery pack for a bike light, and just have a basic
question
about what gauge wires & connectors I should use.

What I'm putting together is about 35watts of headlights with 13.2 volts
(11
Nimh D cells). I believe that works out to 2.65 amps? Ok, so I'm
connecting the cells by soldering strips of 1/8" copper braid, which
according to one source are approx. 18 awg with a current capacity of 16
amps. So that should be plenty for my setup, correct? I just wanted to
make sure I'm not missing something here, because the braid looks pretty
wimpy. Would there be any advantage to using something thicker?

Also, I'll have about three feet of wire connecting the battery to the
headlights -- any suggestions on what would be the proper guage to use?

Thanks,

- mark
Click to expand...
 
Jerry G. <jerryg50@hotmail.com> wrote:
: You can use a stranded AWG 14 to AWG 16 to be safe. Thicker wire is more
: efficient, less loss, and has less chance of any overheating. You are going
: to use a lot of current.

I've heard this before (which is why I was asking), but I was hoping to get
a better understanding of how this works. I.e. if I've got 2.65 amps of
current, why wouldn't a connector with a 16 amp capacity be plenty? And how
would I objectively determine what is enough?

: As for the connectors, you can use the same type
: that are on the small trailers. Check with an automotive shop.

: There are much more efficient lamps for bicycles. There is now the new solid
: state LED types coming out now.

I have a Cateye 5-LED headlight that I switch to when my current battery
pack runs out of juice. It works great to make me visible to other traffic,
but it doesn't do much for helping me see the road. I'm not aware of any
existing LED setup that can compare to a halogen headlight.

: You are going to peddling around a lot of
: weight in batteries. Also, you won't get more than about 2.5 hours out of
: them at full brightness.

Well, I'm not racing, just commuting, so weight isn't much of a factor --
I'll just strap it to my bike rack. As for burn time, 2.5 hours would be
plenty, as I'm only getting about half that now, with just a twenty watt
light. I just need to be able to make it home before the juice runs out.
Actually, though, these are marked as 9000mAh cells, so best case should be
35 watts for 3.39 hours, if I've calculated correctly. I figure with the
extra juice I can also add some really big LED tail lights to replace my
little blinkie tail light.

- mark
 
CWatters <colin.watters@pandorabox.be> wrote:
: Out of interest how are you planning to charge 11 NiMH cells?

I got one of these:

http://www.hobbytron.net/R-DN-1.html

It's called "Dr. NiCad", though it says it works for NiMH, too. It uses
negative Delta-V to prevent overcharging, though from what I've read I
should really have a charger that monitors the change in battery temperature.
I chose this one mainly because it charges at 1.5 amps, so I should be able
to get a complete charge overnight. It's the only smart charger I could
find that could charge fast enough.

- mark
 
"Mark Vieselmeyer" <mviesel@hpb15424.boi.hp.com> wrote in message
news:401000e8@usenet01.boi.hp.com...
CWatters <colin.watters@pandorabox.be> wrote:
: Out of interest how are you planning to charge 11 NiMH cells?

I got one of these:

http://www.hobbytron.net/R-DN-1.html

It's called "Dr. NiCad", though it says it works for NiMH, too. It uses
negative Delta-V to prevent overcharging, though from what I've read I
should really have a charger that monitors the change in battery
temperature.
I chose this one mainly because it charges at 1.5 amps, so I should be
able
to get a complete charge overnight. It's the only smart charger I could
find that could charge fast enough.
Click to expand...
There are very fast chargers available but once you get over 7 or 8 cells
they become quite expensive because they need to step up the voltage if a
car battery is used as the source.. At the top end, competition model
aircraft enthusiasts (F5B competion class) use a German charger costing
$800 ! that will handle 30+ cells at upto 6-8A !!
Click to expand...
http://www.schulze-elektronik-gmbh.de/prs10_e.htm

But thats a bit extreem. Schulze does make cheaper models and they are
available in the USA.

The best fast charge technique for NiMH seems to be a sensitive peak
detector with temperature cut-off as a safety backup.

I'm not sure which size of cell you are using but a good cell for powering
model aircraft seems to be the GP 3300mAH (a SubC size cell). These have a
good energy density/weight ratio and work well at 30-60A. For competition
purporses they are even being used to at 170-200A in 4 second bursts - so
don't short them out!
 
CWatters <colin.watters@pandorabox.be> wrote:
:> : Out of interest how are you planning to charge 11 NiMH cells?
:>
:> I got one of these:
:>
:> http://www.hobbytron.net/R-DN-1.html

: There are very fast chargers available but once you get over 7 or 8 cells
: they become quite expensive because they need to step up the voltage if a
: car battery is used as the source..

It hadn't occured to me that the charger's voltage determined how many
cells could be charged -- I was only considering the amp hour capacity of my
battery pack. My charger uses a 12V DC adaptor as input, so I suppose that
implies a 10 cell limit. From their website it says "runs on 12 to 15 VDC",
so I suppose I could just get a 15V adaptor. What problems would I have if
I try to charge 11 cells with 12V?

Thanks,

- mark
 
"Mark Vieselmeyer" <mviesel@hpb15424.boi.hp.com> wrote in message
news:40115a5c@usenet01.boi.hp.com...

It hadn't occured to me that the charger's voltage determined how many
cells could be charged -- I was only considering the amp hour capacity of
my
battery pack. My charger uses a 12V DC adaptor as input, so I suppose
that
implies a 10 cell limit.
Click to expand...
No it's worse than that. On charge the cell voltage increases above 1.2V per
cell. On old tired NiCad cells it can reach 1.4-1.5V per cell which is why I
said 7 or 8 cells (8 x 1.4 = 11.2V) is the price break point for a charger
that uses a 12V car battery as it's source.

From their website it says "runs on 12 to 15 VDC",
Click to expand...
That might be the clue. It may well NEED 15V to charge 10 cells - you best
check.

so I suppose I could just get a 15V adaptor. What problems would I have
if
I try to charge 11 cells with 12V?
Click to expand...
Even assuming a nominal 1.2V per cell then 11 x 1.2 = 13.2V so it won't
charge 11 cells from a 12V car battery UNLESS it has a built in step up
converter.

If it's a problem I would consider changing over to a 6 cell system (eg make
two 6 cell packs and carry one as a spare).

In another reply you said the cells are marked 9000mAh. What physical size
are these cells?

Colin
 
CWatters <colin.watters@pandorabox.be> wrote:
: "Mark Vieselmeyer" <mviesel@hpb15424.boi.hp.com> wrote in message

:> My charger uses a 12V DC adaptor as input, so I suppose that
:> implies a 10 cell limit.

: No it's worse than that. On charge the cell voltage increases above 1.2V per
: cell. On old tired NiCad cells it can reach 1.4-1.5V per cell which is why I
: said 7 or 8 cells (8 x 1.4 = 11.2V) is the price break point for a charger
: that uses a 12V car battery as it's source.

:> From their website it says "runs on 12 to 15 VDC",

: That might be the clue. It may well NEED 15V to charge 10 cells - you best
: check.

If that's the case, then I think I'll just build it with 10 cells -- my
bike lights are actually 12V, but I was going to overvolt a bit to squeeze
out a little more light. That's just overkill, though.

: [ ... ]
: In another reply you said the cells are marked 9000mAh. What physical size
: are these cells?

They're D cells: http://www.batterymart.com/battery.mv?p=BAT-D-9000BT

- mark
 
Mark Vieselmeyer wrote:
Hello,

I'm building a battery pack for a bike light, and just have a basic question
about what gauge wires & connectors I should use.

What I'm putting together is about 35watts of headlights with 13.2 volts (11
Nimh D cells). I believe that works out to 2.65 amps? Ok, so I'm
connecting the cells by soldering strips of 1/8" copper braid, which
according to one source are approx. 18 awg with a current capacity of 16
amps. So that should be plenty for my setup, correct? I just wanted to
make sure I'm not missing something here, because the braid looks pretty
wimpy. Would there be any advantage to using something thicker?

Also, I'll have about three feet of wire connecting the battery to the
headlights -- any suggestions on what would be the proper guage to use?

Thanks,

- mark
Click to expand...

The braid is plenty big enough. Overkill, in fact. I use appliance
(coffee pot; crock pot, etc.) zip cord for the longer run.
 
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