battery pack question

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.

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Greetings,

Jerry Greenberg GLG Technologies GLG ========================================= WebPage

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?

question

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Jerry G. 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

- mark

CWatters wrote: : Out of interest how are you planning to charge 11 NiMH cells?

I got one of these:

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

temperature.

able

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

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 wrote: :> : Out of interest how are you planning to charge 11 NiMH cells? :>

:> I got one of these: :>

:>

: 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

my

that

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.

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

if

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

: 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:

- mark

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