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Advice for small battery

Alicanto

New Member
Joined
May 18, 2024
Messages
4
Location
Netherlands
Hi all,

I'm new to this forum, so nice to meet you all :)

I'd like to build a small LiFePo4 pack for my campervan. The main purpose is to learn about all the components as practice for a bigger system (next campervan). I don't plan on running the fridge from the battery, so only some lights and maybe charge a macbook or drone batteries. Therefore I'm looking for something cheap, like a 12V 10-50Ah battery.

I'm living in the Netherlands and stumbled upon these cells:

Do you have any recommendations on a BMS for them? Preferably cheap but sufficient (Aliexpress?).
Or cheaper cells of decent quality from Alibaba? Preferably with EU warehouse? 100Ah is also fine if they are cheap.

I was also looking at the Alibaba sellers (Jenny Wu Docan), but the 280-300Ah cells seem to be the popular choice and with the high shipping costs included it will be > 300 eur, which is more than I'm willing to spend on this van's battery.

Thanks in advance!
 
EU stock. No idea about the seller.
 
A ready built battery may be a safer solution,

Around the same cost as 4 cells and includes the built in bms.
 
Or if you want the experience of building a battery pack, for the educational value, you could try those local to you 32Ah cells and order a JK or JBD 4s BMS and have some fun with it.
I started with DIY E-Bike packs using cyl cells 18650's and had a lot of fun with these, and got some confidence in my work before moving on to bigger projects and prismatic cells. I like the learning opportunities, but that is me.
 
A ready built battery may be a safer solution,

Around the same cost as 4 cells and includes the built in bms.
Thanks! This seems like a good deal. :) Going to order it.
You can directly connect this to the car starting battery / alternator, right? With only a fuse in between.

Not really solar / batteries related so maybe a bit off-topic, but I also need a component to connect my fridge to the alternator. I only want to power the fridge when the motor is running and not from the battery. I will use propane/butane to power it when the motor is not running.
So I think I need something that only lets current trough when the voltage is about 14V and shuts it off when going back down to 12V. Should I google for 'low voltage cutoff' or something is there a different name for these things?

Or if you want the experience of building a battery pack, for the educational value, you could try those local to you 32Ah cells and order a JK or JBD 4s BMS and have some fun with it.
I started with DIY E-Bike packs using cyl cells 18650's and had a lot of fun with these, and got some confidence in my work before moving on to bigger projects and prismatic cells. I like the learning opportunities, but that is me.
Well yes and no. I do enjoy building the pack, but for now the convenience and price of that pre-built one wins. Mainly because I have lots of other things to do (such as installing solar! 10 x 450Wp panels!) and not enough time...
Probably for the next campervan with 100-300Ah battery I will build my own pack then. I also have plenty of 18650's and a spotwelder, so can play around with those for the educational experience :)

Would this bms be a good choice for a 30Ah pack?
€28 seems in proportion when spending up to €100 on the cells

And maybe this one for a 100-300Ah pack?
 
can directly connect this to the car starting battery / alternator, right? With only a fuse in between.
There may be a problem connecting a lithium battery direct to the starter battery. It's recomended to use a DC to DC converter/charger to limit and control the charge current. A 30Ah battery will have a recomended charge current of less than 15 amps.
only lets current trough when the voltage is about 14V
You need a voltage controlled relay , split charge relay, for this, example,
 
Ah I see. Thanks, but the BMS takes care of limiting the charging current, doesn't it? It will be connected to an old 'dumb' alternator + starting battery, so a simple relay will do.

Thanks for linking the maypole! That's a cheap solution that does exactly what I need.

A friend also linked this one: https://www.vevor.nl/batterij-isola...len-4m-140a-spanningmeetrelais-p_010263671729
What do you think? It's convenient that already all the terminals and wiring are included, but maybe a bit oversized (140A) for my application. I just measured the fridge uses 135W when connected to 230V A/C, so I assume it will be similar from 12V D/C, so 11A.

11A from the fridge + 15A for charging the battery is still within the maypole's 30A rating.
Maybe I'll order the maypole and look for cables and terminals for 30A as well.
 
but the BMS takes care of limiting the charging current, doesn't it?
Not really. Think of the BMS as a fuse. It can stop current flow if something goes wrong, but it should not be the device controlling the current limits. Most BMS units monitor the cells voltage, current flow, and may have a couple temp sensors. Then if anything goes out of spec, it just turns off the current flow completely.

Your charge power source should limit the current and provide the proper charge profile for the cells. The loads should have a low voltage shut off that stops the load before the cells drain too low. The BMS will try to keep the cells balanced, but if any one cell goes too high or too low, again, it just turns off. And some can be tricky to turn back on.
 
Ah thank you for pointing that out.
I'm a bit disappointed since that would more than double the costs (€110 for the cells + bms and €155 for a DC-DC charge controller), so €265 excluding cables etc. I think it's fine to spend €200 on a charge controller for a 300Ah battery, but think it might not be worth it for such a tiny one.

Then it would actually be tempting to not go the lithium direction, buy a simple 50Ah lead semi-traction battery for €75 and connect it using one of those €45 relays incl cables / terminals / fuseboxes for a total of €120. Or simply run everything from the starting battery :confused: T.b.h. option 1 below seems the best now and then later for the next van build go for option 3, but with bigger batteries, compressor fridge and including solar.

Option 1:
Screenshot 2024-05-19 at 18.31.53.png

Option 2:
Screenshot 2024-05-19 at 18.32.04.png

Option 3:
Screenshot 2024-05-19 at 18.32.14.png
 
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