The battery builders club

[Linesflag]

@MysticalDork

ransparent insulation on speaker wire makes the conductors inside look bigger than they are

I’m not sure that this works that way, but yeah, the pack looks truly awful. All this godforsaken fucking insulation tape

[MysticalDork]

@Linesflag

I’m not that this works that way

The transparent insulation acts as a lens, the same way the glass of a thermometer stem magnifies the tiny capillary of liquid. If you ever break one, you’ll see how tiny the tube actually is when viewed from the end.

[Linesflag]

Yeah I know what you meant, I’m just not sure that this is applicable here. Look at the ends of the b leads, those are definitely overkill for balancing lol

[Battery_Mooch]

IMO the big issue, if see-thru “speaker wire” is used, is that it typically has a low insulation temperature rating. It’s typically 85°C or 105°C and softens at lower than that.

[Battery_Mooch]

@Linesflag

Speaker wire is pretty thick copper, so no objections there, but aren’t the main leads kinda thin?

There is some pretty low gauge (thin) speaker wire available.
Though it doesn’t look like it for this pack.

[TheBoardGarage]

That’s speaker wire? I thought they were McDonald’s straws.

[TheBoardGarage]

12s8p of Molicel P28A. Going into a Carver dual stack.

[glyphiks]

I gotta make a bunch of these packs, so I made up this little glue jig to make that bit a bit quicker

glue up jig

I spent all day cutting nickel. It fucking sucked.

[Linesflag]

@glyphiks

What are those big green spacers for?

[sleepless]

At some quantity, this seems like a job that would be worth outsourcing to a machine shop. Buy sheets in bulk, waterjet/laser into custom shape

[glyphiks]

They keep the two different packs the same size so they fill up the enclosure and require minimal padding.

Also allows me to use the same sized heatshrink and fishpaper end pieces for both packs.

@sleepless yeah i’ve done the math, its well and truly worthwhile, but i have to wait for them to be made and shipped. So in the mean time i have to cut them by hand

[xsynatic]

@sleepless

Have you considered child labor? It’s all the rage these days.

@glyphiks

@glyphiks

I told her that after she checked 100 cells we could go for a skate.

We went for a big skate (by her standards) 8.5km, and when we got home she went straight back into the workshop and said ‘Can I check more cells now?’

[glyphiks]

Always two steps ahead

[Darkie02]

I know battry temp safety limits is largely ignored in eSkate but for those that do add thermisteres might be interested in this on another topic.

@Battery_Mooch

If you are using thermistors for temperature sensing then their extremely slow response time and very poor thermal coupling to the cell can mean a big difference between the temp measurement and the actual cell temp.

The mounting of the thermistors is critical if the pack will be reaching high temperatures and the slow response time will need to be factored in if the cells are being used hard for short periods (where thermistors can’t keep up with the true temp changes).

@Darkie02

What would you recommend? My bodget methods so fare have included keption tape and hot glue in the crack between 2 cells.

@Battery_Mooch

Anything that can firmly hold the thermistor to as large a cell surface area as possible and increase the rate of heat transfer is good. Pressing it down between cells, firmly against both cells, is good and using hot glue can help transfer heat to the thermistor.

If I have to use a thermistor (instead of thermocouples) I like to embed the thermistor in a blob of thermal paste and press it firmly against the cell(s). It’s easier to force the paste into all the air spaces around the thermistor bead, it conducts heat better than other materials we can use, and cleans up fairly quickly.

Also tape down at least a cm or two of the thermistor wires to one of the cells as this helps keep the wires from sinking away any heat from the thermistor bead.

A lot depends on whether this is for testing or for a pack going to a client. If this is a permanent thermistor install for a client pack I would thermal epoxy the thermistor in place. Kapton tape over it to hold it in place and hold down the wires.

Hot glue can soften if the pack gets too warm and this could lead to the thermistor losing some of its already very limited contact with the cells.

[tech.shit]

Mooch is 100% right about this.

It’s a thermal probe. You want to give it the best thermal conductivity to whatever you’re trying to measure the temperature of. Thermal paste is a great tool for this.

Mind, if you’re measuring something else with the thermistor like the BMS it’s self you want to attach it to that.

Point is just leaving a thermistor loose in your pack is about as useful as checking the temp with rectal thermometer from the outside of the esk8

[J0ker]

So the ltt smart bms is pretty accurate in my experience. Have checked with 2 different thermometers and its within .5° of the bms reading.

That’s not to say @Battery_Mooch isn’t correct. Just saying MY ltt is pretty much spot on for my liking.

[Battery_Mooch]

Excellent!
This was during use or at room temp?

[J0ker]

Both. Under non operational use it reads average room temperature. I can even pull it from the enclosure and it notices fairly quickly the temp change.

Under operational use (let’s say the bench) I can watch temps rise and fall according to throttle and brake. Takes about a second for values to change but they change accordingly.

[Battery_Mooch]

Great, thanks.
For everyone else…the biggest issue with thermistors is typically not their base accuracy but their slow response time. That’s what can lead to temp readings that are much too low when the temps are changing relatively quickly, when accelerating for example. Some thermistors have response times over a minute. They start to respond almost instantly but take a very long time to settle at the actual temp.

@J0ker, glad that you are not seeing this and that your thermistors reach the true temp quickly.

[marketthrowaway]

@Fosterqc

Vat de fak is thees