Hi From Central Coast NSW

slimf

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Hi everyone, David here from Central Coast NSW.

I run a web/email hosting&web design business during the day but am here to learn moreabout building 18650 packs.

Im 40ish now, but Im the past have completed electronics courses at TAFE, so know my way around a soldering iron and the basics of electronic theory. (Its been a while)

I have two projects planned..

1. Small battery pack for my kids 12v Quad bike. This will replace a12v -12ah lead acid battery. This is really just a fun / quick project to get used to testing cells and assembling them into packs.

I do need some advice on a BMS for such a pack. Im thinking of 4s and as many p as I can fit into the space. Probably 5 or 6p.

I can always charge this pack with my hobby charger - and can do it with balance leads. Maybe I dont need a bms?

2. Adecent size camping pack to power camping fridge, freezer, lights and phone chargers. Probably in the range of 200ah. I wont attempt this till I am familiar with how Im going to charge and maintain the beast.

There are a few camping threads on here but none really cover making a camping battery. Im thinking 4s but I will have 2x 160w (320w)solar panels that will need to charge this pack as well as being able to charge from the car alternator while driving. My current lead acid setup has amppt dc-dc charger but these are suitable for lead acid/agm batteries. Any advice heres would beappreciated. Somthing like a MPT-7210A - this device is only suitible for 24v packs and up thou.

Ill besure to post some picks of the packs during their build.

Thanks David
 
Welcome!

1. 3S and 4S lithium is both not ideal for 12V. Check what the electric motor and its controller, if there is one, can handle. 3S is usually too low, 4S is too high. If you want to use a BMS or not depends. There are no definitive rules for when a BMS is NEEDED. It is never needed, but it can do certain things for you, like balance charging or low voltage cutoff amongst other things. It is generally helpful to achieve a high level of automation. However, if you can manage without then you can do that as well. I wouldn't use a BMS in such an application.

2. Is this supposed to be mobile or a fixed installation in a camper van or something? Your car probably produces 14.4V maximum so that is not high enough. But even if it was high enough, you can't charge the battery directly from it as there is no current limit. You probably need to run a charger from the cars onboard system to charge the battery if you really need this.
Also you should think about a 7S system, 24V. But if this is viable depends on your equipment. Charging the battery with a charge controller made for lead acid batteries isn't impossible but isn't very convenient either. There are charge controllers suitable for lithium but these are generally bigger devices. Smaller and cheaper ones are probably coming in the future.
 
Hey!

1. No bms is needed. Go with 4s if the controller handles it. You get a bit more umph. Just balance charge them and you are good to go.



2. I think DarkRaven answered that one. I have done somewhat like that but alot smaller. Its doable.
 
Welcome from Lisarow!
Yes as per darkraven your camping pack will be better at 24volts but will require a sizable DC-DC converter for most camping type loads. I think solar and vehicle charging will need separate charging devices?
 
THanks for the responses everyone.

The kids quad is a simple beast. Sealed 12v lead acid, there is no speed controller as such - it has two speeds, slow and fast which is switchable by the kids. Not sure how it achieves the two speeds.

I cant see slightly more voltage hurting it thou.. I might just build a fused 4s pack with no BMS for this one.

The camping battery needs to be around 12v - It will be portable and directly power camping fridges, lights etc.. All designed to run off 12v automotive style voltages.

Hoping 4s won't kill anything - the hardest part will be charging it via either solar or via the cars alternator supply. I know I will need some sort of DC-DC charger, but they seem to be hard to find.
 
Well today was different! I obtained 500 Samsung 26q batteries today..

My plan was to build a small pack for my Kids quad and then a larger camping pack, but with this many cells I could jump in to 7s powerwall with 80p (almost anyway, would still need a few more cells)

Hmm what to do.



Sent from my iPhone using Tapatalk
 
Just a comment on the "no BMS needed" thing... I built a 2p10s ebike battery a while ago, new cells, soldered them together. But since my soldering skills just suck (my tips keep oxidizing for some reason), a couple of the joints were a bit cold; after a while, the bike would not give to much oompph, so I cut open the battery only to find that a solder joint was broken, hence on earth of the batteries was down to or 0.6V. It recovered fine (new cell, remember?), but then added a BMS that will protect from this from happening again. BMS in a high-vibration application is a good idea.
 
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