Will wood short or drain a 50v battery?

Batteries, Chargers, and Battery Management Systems.
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veloman   1 GW

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Will wood short or drain a 50v battery?

Post by veloman » Nov 08 2010 6:37pm

I'm building a battery that has a peak voltage of 50v, and want to make sure that I don't short it. Is there any way that wood could short it? (I'm using a slim piece of wood to hold my connectors).

(I couldn't get an answer in the 'building cylindrical battery for dummies thread")
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Re: Will wood short or drain a 50v battery?

Post by battman » Nov 08 2010 6:50pm

I wouldn't expect so but here are a couple of thoughts:
1) I don't know what kind of wood you are using, but, and this is way out there, if it was some kind of composite and contained other conductive materials, then maybe it could short or drain your battery. Why not test the electrical resistance of your wood to see if it is somewhat conductive? If it is then you could coat it with varnish. But then the question is "will varnish short or drain a 50v battery?" ... and then the electrical resistance of the varnish must be tested. And if it conducts then a layer of rubber could be added over the varnish, more testing and so on until a vast onion of materials is used to mount the connectors!
2) Even if the connectors are protected from water, is there a chance that the wood could be exposed to water? If so, it could suck up some and start to conduct.
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Re: Will wood short or drain a 50v battery?

Post by Ypedal » Nov 08 2010 6:51pm

Dry Wood , no problem at all.

The wood itself is not conductive, but heavy moisture combined with sap " can " be... but i've used wood without any problems on packs.
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Re: Will wood short or drain a 50v battery?

Post by GreenKnight » Nov 08 2010 7:01pm

Dry hardwoods are generally not a problem and are often used for electric fence supports (do conduct a little when wet but will dry out again in the sunshine) Softwoods absorb a lot more water and often have sufficient salts to act as conductors. Not going to pull mega amps but over several weeks would significantly effect the state of charge.
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Toorbough ULL-Zeveigh   10 MW

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Re: Will wood short or drain a 50v battery?

Post by Toorbough ULL-Zeveigh » Nov 08 2010 7:05pm

wood retains moisture so yes, there is a way.
wood have to be pretty wet tho to short as well as form a complete circuit, may get a slo drain.
50V is kinda at the cusp where you'd rather not take the chance.
since uve sold ur lipo what kind of battery is it?


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Re: Will wood short or drain a 50v battery?

Post by neptronix » Nov 08 2010 8:15pm

I had a conversation like this with a guy at home depot trying to figure out what material to use for my battery box..
He said wood retains moisture and that's bad news for electronics..
Also.. it doesn't fare too well out in the elements! Especially if you live in a rainy area.

So i decided on aluminum with a protective rubber sheeting.

By the way, wood is not conductive in any way.. bust out your multimeter and set it to test continuity if you don't believe me :)
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Re: Will wood short or drain a 50v battery?

Post by Ypedal » Nov 08 2010 8:44pm

Polycarbonate, ABS plastic sheet, G10 or Bakelite ( fiberglass sheets ) , carbon fiber, corrugated plastic ( voting signs ) , Flooring Tiles ( peel'n stick tiles !! ) .. many other better options.
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Re: Will wood short or drain a 50v battery?

Post by katou » Nov 08 2010 9:05pm

The reason to use solid wood is the ease of access, low price, strength/weight ratio, and ease of attaching fasteners.

Very few materials can beat wood in these areas.

Buy the pine board at HD that has the straightest grain in 1/2". If the boards are all bowed/cupped, plywood is a good next choice, but only if you can get plywood with at least 3 laminations or better. Construction grade will NOT do it, go for paint grade, one handi-panel should do it. Get the higher lam-count Russian or Baltic Birch plywood. It's heavier, but very, very strong.

Yes, it is hygroscopic. If you want to waterproof it, that is only a coat of epoxy or two away.

I'm using wood, no contest. Foamed PVC was also in the running for a short time. Hard to get though.

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Re: Will wood short or drain a 50v battery?

Post by Gordo » Nov 08 2010 9:09pm

neptronix wrote:I had a conversation like this with a guy at home depot trying to figure out what material to use for my battery box..
He said wood retains moisture and that's bad news for electronics..
Also.. it doesn't fare too well out in the elements! Especially if you live in a rainy area.

So i decided on aluminum with a protective rubber sheeting.

By the way, wood is not conductive in any way.. bust out your multimeter and set it to test continuity if you don't believe me :)
How did the old moisture meters work? The ones with the two probes on the end?
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Re: Will wood short or drain a 50v battery?

Post by neptronix » Nov 08 2010 9:12pm

I think i missed that part of science class ;)
Water is conductive to some degree, right? I think your battery box would have to be pretty dang wet for it to be conductive though. If that occurs, you got other problems !
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Re: Will wood short or drain a 50v battery?

Post by Ypedal » Nov 08 2010 9:16pm

RO DI ( Reverse Osmosis, De Ionized ) water is pretty much non conductive. Dirty water is !
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Re: Will wood short or drain a 50v battery?

Post by 999zip999 » Nov 08 2010 9:46pm

My ungle had a electric fence it had an cerimic insolator then wire 3 ft. from the top of the wood pole.I touch the top of the pole. I got a good jolt . it was damp.

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Re: Will wood short or drain a 50v battery?

Post by neptronix » Nov 08 2010 10:00pm

Ypedal wrote:RO DI ( Reverse Osmosis, De Ionized ) water is pretty much non conductive. Dirty water is !
Hm! always something to learn here on ES :D

So Veloman, you get the idea yet? :)
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veloman   1 GW

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Re: Will wood short or drain a 50v battery?

Post by veloman » Nov 08 2010 10:31pm

Yeah, I'll prob look for a piece of plastic to use.

But wait, I used a glue gun to attack my connectors to the wood. I wouldn't bet my life on it, but I'm pretty sure the glue is separating the metal parts. Glue is a good insulator, no?

The wood I am using is a thin sheet of composite, it's such a tiny piece that I could replace it without too much work.


But I did finish my battery!! It's just 24 konion cells from a few makita packs. 44v 3ah OR 22v 6ah, depending on how I change the connections. I did this because I will be running it at 44v on the bike and charging at 22v on the Meanwell. There were various other reasons I got a 24v MW, and I'm really trying to keep costs down.

Yes this is a TINY battery, just enough for 8 miles of easy assist riding, which is all I need to go into town and back. The motor I am using pulls a peak of about 20amps, around 17 sustained peak. So I figure a C rate of 6c should be fine, plus I will ride conservatively, rarely going over 12amps.

Ultimately I plan on moving to a city where I don't need more than 8 miles range anyway.

The big lesson I learned here: it takes a TON of work to build your own battery. The amount of hours I spent on this battery is crazy. Sure, I don't have the right materials and tools, that would help a lot.

Advice to newbs who aren't totally sure they want to take on battery building - Just buy a ready to use LifePo4 or something.

I am happy that I finished, because now I can say I am riding on pure recycled batteries - essentially zero environmental impact.

Now I just need to add some wires to the connectors and test ride it tomorrow.
Attachments
10-9-10 032.jpg
This is the wood piece in question. The voltmeter doesn't pick up anything through it.
10-9-10 032.jpg (36.12 KiB) Viewed 1228 times
10-9-10 034.jpg
Started with this, but it needed more support, especially with spring tension.
10-9-10 034.jpg (79.62 KiB) Viewed 569 times
10-9-10 037.jpg
Final product. Nearly doubled the weight with all that wood, used a 2x4 for the main backing. But it's all tensioned and secure.
10-9-10 037.jpg (80.22 KiB) Viewed 648 times
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Re: Will wood short or drain a 50v battery?

Post by Ypedal » Nov 09 2010 7:32am

Absolutely, building a pack from recycled cells is a HUGE job, not all that complicated but very time consuming..

a few things, at 6C, those cells will get hot, enough to make that hot glue soft, springs are far from being the best idea as they can wiggle and cause cutouts while you ride, and they are high resistance, ok for flashlights, not ok for an ebike..

It should work, but there are better ways ! :wink:
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texaspyro   100 kW

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Re: Will wood short or drain a 50v battery?

Post by texaspyro » Nov 09 2010 7:58am

Gordo wrote:How did the old moisture meters work? The ones with the two probes on the end?
Wood is most definitely (but slightly) conductive. The higher the moisture content, the lower the resistance. Different woods have different conductivities. My moisture meter has a calibration table for the species.

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Re: Will wood short or drain a 50v battery?

Post by katou » Nov 09 2010 12:30pm

If you have hot glue in contact with current-carrying metal, you may have a problem.

If you have A123 cells (high-C rate) then you might be fine. However, since you stated that the cells are recycled, that means two things:

1. cells may not be in top shape, so C-rate should be derated from manufacturer specs
2. cells are most likely not high-C rated (most Moli cells and others are happy around 3-4c)

I did what you (I think) did with some hot glue somewhere in there holding things together, and then I tested a cell at 5c on my CBA III.

The hot glue melted, and that was with an A123 cell. The moli cells would get hotter.

YMMV but regardless, bravo on making your pack. I'm just starting on mine. I've spent about 6 months learning about batteries, charging, BMS, construction, electrical theory, so I know what you mean about the front-loading on the learning curve.

That said, I simply do not have $900 to spend on an ebike pack. Heck, compared to the battery/charger cost, ebike mechanical stuff is cheap!

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Re: Will wood short or drain a 50v battery?

Post by rguy56 » Nov 10 2010 1:38am

It's lovely that simple questions can be ruminated on forever.

Wood will not short your battery. You expect to be a regular user, so throttle use will be your major drain. Yahoo!

Don't get me wrong...I love the discourse that comes from these questions. For deeper thinkers than me, don't let me stop you. My hat's off to you...err how much does that increase my wind resistance?

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Re: Will wood short or drain a 50v battery?

Post by Gordo » Nov 11 2010 1:14pm

I find value in most threads on ES. Many of us don't know enough to come in out of the rain, so it doesn't do any harm to puzzle through what appears as a simple, frivolous problem. On good point I have picked up from this discussion is no one appears to be aware of HOT, HOT GLUE. Everyone appears to be using the cheap crap from HD which emulates a dose of clap at 50*C (105*F for the metrically challenged). Most inexpensive glue guns will handle 100*C glue sticks. This would be more suited to a battery pack or other toasty application. If you look around, you can find 235*C hot glue which is used to fingerjoint wood. This stuff will char the wood, if not immediately cooled after application.
Just some more mindless babble.
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Re: Will wood short or drain a 50v battery?

Post by katou » Nov 11 2010 7:06pm

Wait a minute, does this mean that you weren't serious about the hat/air resistance thing?

I had a bunch of information from leading testing laboratories regarding the best style of hat for minimal front cross-sections, but just for that, I'm not posting it.

Ha! Take that!

Katou


ps. good info about the thermal rating of the hot glue. I never thought to check.

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veloman   1 GW

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Re: Will wood short or drain a 50v battery?

Post by veloman » Nov 11 2010 8:06pm

Well I've learned some things in this thread.

I'm scrapping this battery pack. Will either solder the cells or have them tab welded. None of this spring/wood crap.


Bad design, money spent, but lessons learned.
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Re: Will wood short or drain a 50v battery?

Post by GreenKnight » Nov 12 2010 7:37pm

For a physical container of the batteries, wood sealed with an epoxy or polyester resin/glass fibre coating would be ideal.
Extremely low electrical conductivity, extremely water resistant and strong.

Best electrical contact for cell to cell I would aim for soldered or welded connections.
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