Battery Build - Trek wood triangle

[katou]

I am starting to build my first battery for a hub motor 9c in a Trek 700c commuter.

Here is the start of the pattern:

View attachment IMG_3659.JPG

Here is transferring the pattern to a piece of flat material (easier to take notes on, and more true. The wooden pieces sometimes flex)

View attachment IMG_3660.JPG

Now we put the flat pattern in the triangle, and... it doesn't fit. I had to sand off a bit to get it to go in there. The wooden pieces did indeed flex around some obstacles, like the bosses for the water bottle cages.

Now it fits!



The idea here is to use Leamcorp's battery box tech to fit a small 36v 10ah A123 pack in there. This is actual size:

View attachment IMG_3678.JPG

And this is how it will fit in the space:

View attachment Chosen Battery Box.JPG

That's as far as I've gotten so far, I'm deep into testing the cells that I need, hope to start cutting bits of wood soon.
Oh, the attachment points are going to be Riv-Nuts that I got from a local fastener place. They're only aluminum, but hopefully that will be enough.

Wish me luck!

Katou

 

[minde28383]

This may be little out of topic but what charger you will use to charge these a123 cuties? I also have plans to build pack from a123 in the near future, but not sure what charger to use and how to balance these batteries. I have Turningy 6cels 5Amps charger, but such pack would require more capable&powerfull charger.

 

[katou]

rkosiorek modified Meanwell. (he's a member, and an electronics genius.)

The reasons we went with Meanwell (me and a buddy are doing the same thing)

1. cost is cheaper than existing LiFePo chargers
2. voltage can be exact to needed spec (3.6 x # of serial groups) rather than 4.2v of LiFePo
3. cost is similar to SLA chargers, but SLA chargers hit High Voltage Cutoff (HVC) then go to a lower Float voltage. That's not what we want, we want the charger to hit HVC and then hold there to allow cells to all come up to the same State of Charge (SOC)

So, either LiFePo or SLA charger will undercharge our pack, and cost more than a modified Meanwell. You just have to find someone to mod it for you! :wink:

A few of those A123's would grease the wheels I'm sure. Where are you getting yours BTW?

Katou

 

[katou]

I have decided to make the triangle space 4" wide, plus 1/4" ply sides means total thickness of 4.5" between the knees.

I saw a reference to 4" being a good design goal for overall thickness between the knees, this is a bit over. Hmmm.

Well, easier to make it thinner than the other way around.

Off to cut some wood.

Katou

 

[dogman dan]

4" would be narrow enough to never really notice. 4.5 will still be quite tolerable. My race bike has 6" wide, and I find it still pedalable, though I wouldn't like it on a street rider, mostly for how it would be when you stopped at lights. If you can, make it roundish on the top edge for comfort when you stand over it.

 

[katou]

Good idea. I'll see if I can squeeze it a bit smaller, and I will make the top piece thick enough to sand the edges round.

Still haven't cut the wood, have the fix the bathroom door first. No bathroom door makes the guests really nervous.

Katou

 

[minde28383]

...

A few of those A123's would grease the wheels I'm sure. Where are you getting yours BTW?

Katou[/quote]

well, sure they would I bought 10 cells of a123 six months ago on ebay for my balza plane, but my fly project is at deadlock, so I assume I could make some pack for ebike. I need to get more of these a123. I plan to make 8Ah or so for short trips. Plus it would be ~40% lighter than my 15Ah ping.

 

[katou]

Check the For Sale Used section, you can sometimes find really good deals there.

Katou

 

[katou]

Here's the latest:

View attachment IMG_3816 small.jpg

And another view



The small offset you see at the top of the battery box (bottom of picture because bike is upside down) is for the 1/4" panels that will go on each side, so that they mount flush. One panel will be glued on, the other will be removable to access the interior.

The large double piece of pine at the top (bottom) is there so that I can shape the corner into a nice rounded edge.

Things feel like they're moving a bit now, updates will be faster I hope.

Oh, the bolts in the picture go into Riv-nuts that I put into the frame tubes. Can't see 'em, but they're there. I'm going to do a little photo-essay on putting in the Rivnuts, so if that interests you, keep your eyes open. I'll link from here for anyone who wants to follow along.

Katou

 

[The Mighty Volt]

Katou, how do you find the meanwell switching supply works as a charger?

I just bought one off ebay, a 27v variant, adjustable to 32v via the toggle.

I hope to charge a 28v pack off it.

Thanks.

 

[katou]

Unfortunately, the mod is proving more difficult than planned, so the Meanwell unit is not finished yet.

But I'll be happy to let you know, as soon as I can try them out!

Katou

 

[The Mighty Volt]

Unfortunately, the mod is proving more difficult than planned, so the Meanwell unit is not finished yet.

But I'll be happy to let you know, as soon as I can try them out!

Katou

I thought they just provided a straight voltage supply, like a transformer or something. No?

Thanks.

 

[katou]

You can't use a transformer to get the voltage that you want. This is because transformers only work with AC electricity. We need DC to charge our batteries, so, we can't use a transformer. Bummer. Transformers are nearly 100% efficient!

BTW, this is why we have AC power in our walls. We want to use transformers, transformers only use AC. Voila, all our electricity delivery systems use AC. I'm leaving out most of the historical bits regarding the feud between Edison and Tesla, but that's the bare bones of the functional reasons for AC as I understand them.

Anyway, why use a Meanwell:

A Meanwell brand power supply is just one way to get DC electricity from the wall (AC electricity) at the right voltage and amperage.

Meanwell power supplies are cheap. Could you use another brand? Absolutely. Could you use a power supply designed for a computer? Sure.

The other big reason to use a Meanwell brand power supply is that there has been considerable research on this forum into how to modify them. If you want to get a particular voltage from a Meanwell, it's a good bet someone here has already done it. But you do have to pay attention to the model that they used.

Why modify? Because the voltage coming out of the power supply is pretty close to what we want, but close isn't good enough, and to add constant current capability.

In summary, people modify power supplies for 2 main reasons:

1. The power supply is already constant voltage, but we need the output voltage to be a perfect mulitple of 4.2v (Li-ion cells) or 3.65v (LifePo cells)
2. The power supply may not be constant amperage, and we need that.

It would be easier just to buy what we want, right? Problem being that you can get a Meanwell power supply for $50 and a pro charger is like $100 or more.

Different models of Meanwell power supply have different circuit diagrams, so they require different modifications. As an example, I recently bought a meanwell power supply that a friend is modifying for me. He's having quite a time getting the mod done because the particular model I purchased is a bit tricky.

Best way to go there is to find someone who has done the mod you want, and then walk in their footsteps, repeat their work. Or better yet, find a tech-savvy individual, and give it to them to work on!

Assuming that you can modify the power supply without major headache, a Meanwell power supply is a cheap way to get fairly high rate charging.


Katou


ps. I am not capable of modifying a Meanwell, so don't even ask.

 

[Jeremy Harris]

Just for the record, these Meanwell supplies are pretty reliable, too. I first started that thread on using them as chargers over two years ago and my original 48V modded one (that normally runs at around 59V) is still working fine. I have another, 24V one driving the Turnigy Aerodrive motor on my milling machine. It's been running the milling machine hard for nearly a year now, without getting even vaguely warm.

If you stick to the proven mods then these switched mode supplies work very well indeed and are great value. You couldn't buy a mains transformer, rectifier and regulator for the price of one of these power supplies, plus they are nice and light and not too big, either.

Jeremy