12V packs X 4 or not, & other assorted ?'s

Hi. I'll be getting a live aboard sailboat shortly and I kind of like having a small emergency solar powerbank at home too. So, I'm thinking if I could make my ebike batteries in 12v increments and just hook 4 together for my bike when I need it and that way I could use them for the boat power as well as the home power system...just more versatile all around.FWIW, I plan to keep an ebike on board the boat. The 12V batts could also be easily used in the unlikely event I go with a 36 or 24V ebike system. Any significant problems with doing that? As I understand it, higher voltage is not a problem but we're talking about a choice of around what 16.5V or about 12.5V the way the voltage works out on these 18650's. Seems to me, I'd just about have to go with the 16V, is that OK? And aside from drawbacks from doing it this way, anything else you think I might need to know.

What I know and what I have to work with. I'm not particularly bright with hands on in this but have done a lot of reading. I've never built a pack or had any special training. I've done simple electric repairs most of my life, wired my own house and such so it's not a complete mystery to me, but that's about all. I'd like to end up with about 20AH packs. My batteries include, all new/tested from laptop batteries...about 140pcs all same batteries from 2100 to 2300mAh. A mixed batch of around the same count and capacity (about half those all same) and the 140 or so of the 1800 to 2000mAh I need to ask about.

I thought I'd go with some of the direction from the guy on youtube who did the beginners guide here. Everyone including myself at first, seems to want to rule out anything under 2000mAh but if at all possible, and since I have so many, I'd like to use those for my first builds, unless there is reason other than being just a lower capacity...a few miles or so less per pack won't bother me, and that is if I even use those packs for the ebike.

Thanks for some insight on if this is OK to do and if so, any tips would be helpful. Oh, I'm thinking 30 batteries per single 12V pack or whatever number less than that works out?

Welcome!

You can certainly do that. However, the usual sizes of batteries vary for your applications. Like the bike battery can't power your home and your home battery is too big for the bike. You have to find the sweetspot in between. Apart from capacity you might also get a current issue. You have to figure out what max currents the batteries have to supply. You can never design a battery properly if you don't know about the intended load.

12V doesn't work well with lithium cells, that is correct. 3S too low, 4S too high. So either limited runtime or overvoltage issues. Higher voltage is an issue of course. Or can be.

Your capacity threshold is entirely your own decision, usually based on what you have to work with. If you can afford to only use cells over 2000mAh, then sure, do it. However, if you can't, then you can also use lower ones.

Thanks, You make a good point on exact voltages. It was all right under my nose but the fact that wouldn't work with other batteries of 12/12.5V, escaped me. And to figure all that out at this stage of the game for me anyway, is a bit more than I want to tackle. Are step downs or some type voltage adjuster doable in this area...too expensive? BTW, money matters here.

So, guess it's back to just building a single ebike battery....easy decision.

Ending up with the very low capacity batteries I mentioned was unavoidable when buying batteries the way I was, I took what I could get. So now it's a matter of use them for a low capacity build or not use them at all (I can only power so many flashlights. Oh, found out during Irma, 3'll run my AT&T modem/router for about 4hrs ).

I figure for a first build on the outside chance something goes bad wrong, best to start with those. I'll decide on that but good to know they will work.

Voltage converters (buck, boost or buck/boost, usually buck) are doable but big ones are expensive while small ones are especially cheap at your nearest friendly chinese merchant.
24V to 12V, max 25A / 300W, DC-DC converter from Victron Energy costs about 80 EUR around here, bigger Ruideng DPS DC-DC modules are ~40-50 EUR from China. Small converters around max 8A / 80W or so cost about 10 EUR from China.

I'd always go for purpose made batteries. If you have x different use cases then you build x different batteries. Starting with the smallest one is usually a good idea for training.

What do you mean.."purpose made"?

Not too bad price wise, and thanks, I'll look into those converters. Decided to stick with the basics on this one, but that will be useful for future reference.

I've gotten a few recommendations on the configuration for a 22/24 AH pack but I'd like to hear yours if you have suggestion on that.

No real harm in not using holders, and just gluing these together for the sake of space? I mean I could use them if necessary but I see many don't.

Seems I read the bus bar requires a solid nickel strip, and I was going to get them from ebay/china but there are so many petty scammers there, it concerns me I won't get solid nickel. Is there a way to tell if it's solid or not? I was going to just go with the copper home wiring but I can't seem to find the proper size for this. I would think a single 12guage strand would work because as I understood it, that's what I'm was to, and am using for the main power coming from the battery so I would think that would be enough fo rht battery buss, unless I'm missing something.

"purpose made" means that each set of banks of batteries are designed for that purpose alone. Not a pack that is designed to go in a powerwall one moment, then an ebike another, then a mower another time, etc, etc. Each need would have it's own specific design of pack.

That's exactly what it means.

And yes, you can glue them together if you want. However this makes maintenance complicated if it is required some day. The size of your busbars depends on your load obviously, you need to know how many amps you will draw. You need to know that anyway because reclaimed 18650s from laptop batteries don't do high amps very well.
ickel strips are usually spotwelded. With reclaimed cells you would rather use copper and fusewires and solder your pack together.

Thanks to both of you. After starting with 25amp fuse I worked up to a 40Amp and no longer have blow outs so I guess that's a pretty safe bet on the amperage I draw?

Your right, I had thought about the maintenance difficulties with glue, but somehow got the idea there would be little maintenance. Being my first build though, probably best to go with holders.

I'm now looking for a 48v configuration that will fit on the rack above the rear tire (long) in my desired AH range to copy, then I can start ordering. Any exceptional step by step videos or otherwise out there that you can recommend? I have yet to look this site over, and will do that shortly.

OK on the strips, and now that you mention it, I had considered them when I was going to buy a spot welder, something I've since decided against so will do on that recommendation.

No, you don't design a battery on the specification of the fuse alone. The fuse can give you hints, but is there to protect the wires from getting hot, melting, burning and to protect your devices and yourself before anything else. You have to know how big the load is. And you do that by checking the specification of the devices you are running from the battery.

There are videos about how to build packs on Youtube, easy to find.

Spotwelding maybe is something that you can do with new cells but I would never do that on reclaimed cells. I would always fuse them which you can't do when spotwelding nickel strips onto them.

On battery design, I guess I was thinking these 48V or whatever premade/new batteries for ebikes we buy, must follow a general rule of thumb, but evidently not. Yes, I like the idea of fusing them all, especially when using wire fuses like that

These are new laptop cells, but maybe that's what you mean by reclaimed. Though the little spot welders, as cheap as they are, are tempting I'd decided on soldering them, but what you mention leaves no doubt/1 less decision to ponder.

Yes,. youtube is one of the best options, and it look like I'll have to choose from the easiest to understand there. Thanks. Think I 'll get back there and watch a few more vids clear through...

2 questions, on the fact these batteries don't handle high amps well, and just to make it easy for me to understand, does that mean the more batteries one uses for the pack, the better of they are when using those particular batteries or is my thinking off on that?

Also, I got this little gadget in the mail today for my bike:

http://www.ebay.com/itm/Electric-Gr...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

It appears to have just the two connections, and the large hole is just a mount/empty. I was wondering if anyone happened to know which was positive since it is for an electric car? I'm just worried it's not like a multi meter where a backwards hook up doesn't matter, and I'll blow it....or is it ok to just try it?

To make sure we are talking about the same thing:
Batteries are the end product and are made of cells. Sometimes, especially in bigger setups, we're talking about packs made from cells and then batteries made from packs.
I guess when you're saying "the more batteries one uses for the pack" you mean "the more cells one uses for the battery"?

If so, then yes. More cells means more capacity or energy and the current is spread across more cells which reduces the load on the individual cells, which is good, or simply gives more runtime.

Your device looks like it has an IEC 60320 type connector, specifically a C13/C14 or C15/C16 type: https://en.wikipedia.org/wiki/IEC_60320#Appliance_couplers
I've seen this on bike batteries, but specifically on older ones. They use C13/C14 as a charging port. However, for me they are more common in AC applications where the left pin in neutral, the right pin is live and the top pin is earth. I don't know about their polarity in DC applications and also it looks not 100% like IEC 60320 as you can see.
You can tell by the shape that there should be no way to put it in the wrong way. If it is at all possible in your case then this a probably not meant for your application. As a voltage meter it probably doesn't matter and you get a negative reading because voltage is just the potential between two points. However, as there is also DC-DC conversion going on to power the USB port I can't tell whether it matters or not.

If so, then yes. More cells means more capacity or energy and the current is spread across more cells which reduces the load on the individual cells, which is good, or simply gives more runtime.

Click to expand...

I'll elaborate a little more on this: The more cells that are in "parallel" will load share the amperage during charge/discharge. During discharge, this also gives you a greater potential to draw higher amps. The more in parallel, the more amps can be drawn. So as long as the wiring, fusing, electronics in between can handle it.
Also, the more cells in parallel, the higher the capacity of the pack/string. So, if you had 15 cells in parallel, you'd have 15X the capacity than if you had 15 cells in series. However, the 14 series would be 15X the voltage of the parallel ones.

Korishan said:

Also, the more cells in parallel, the higher the capacity of the pack/string. So, if you had 15 cells in parallel, you'd have 15X the capacity than if you had 15 cells in series. However, the 14 series would be 15X the voltage of the parallel ones.

Click to expand...

Exactly,but capacaty of a 15 cells-pack in parallel or a 15 cells-pack in seriesare the same... (only voltage is different.)
If you have 10 cells of 2000mAh it makes no difference in capacity if they are in parallel orin series, in total it stays 20Ah. ( but 3.7v in parallel and 48v in series).

Edit,

Never mind, i was wrong, Darkraven has enlightened me, it took some time but he did....

The capacity isn't the same, the energy is

Is it not Capacity in mAh ? and Energy in Joules ? Energy can be alldifferent things like mechanical, chemical, ....
We are onlytalking about mAh as unit for capacity, right?.... please correct me if i am wrong.
Abit off topic but we gotta have or units right, very important

Edit:
Joule not Joules

Yes, it is, and yes, we are
Capacity is current over time, energy is power over time. And power is voltage * current.

10 cells, 3.7V nominal voltage and 2Ah each, 3.7V*2Ah = 7.4VAh = 7.4Wh each and 74Wh for 10 cells

10S: 37V nominal, 2Ah, 74Wh
10P: 3.7V nominal, 20Ah, 74Wh

You said it yourself, the voltage is different, but if the voltage is different then the capacity has to be different as well because otherwise the energy within the system wouldn't be the same. And that is not possible. You have put in 74Wh and therefore need to get out 74Wh

You can use Joule as well, it is the SI unit for energy. It is not very common though. 1J = 1VAs = 1Ws (watt second) and there are 3600Ws in 1Wh. You can substitute 1Wh for 3600J in the calculations above if you want.
Ah and Wh aren't SI units, but they are approved for usage within the SI and together with other SI units. That is why Joule is rarely used for electrical energy.

You are 100% correct.... power (Wh) stays the same, capacity (Ah)changes depending on total batterie voltage.
Thanks to correct my correction...

You still haven't got it though

Wh isn't the unit of power. W is the unit of power, Wh is power over time and that is energy. And capacity has nothing to do with voltage. Capacity changes with ne number of cells in parallel, voltage doesn't.

Hahaha,you are right,energyWh stays the same.... but with the Ah changing in a battery iwant to say with more cells in series voltage rises and Ah is lower (= 1 cells Ah )while withmore cells in parallelvoltageis lower (=1 cells voltage)andAh rises....

I have seen the light, i amgetting there...

And the crowd....