Beginners Guide to Processing 18650 Cells | Cell Database


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Mini-Powerwall
#11
I fly quads too Smile

To charge above since you should not go below 80% you need around 1100 + some lossses. So if you need 10 chargs with you go with 15Ah atleast and so forth.

But if you going to charge the batteries skip the AC out... A proper RC charger works on DC and not AC. and if you have a cheap one only doing AC then buy a DC version. You can run it directly on the battery and you save both weight money and efficiency.

At home you run that charger on a Computer PSU or Server PSU is even better. Them you get for free and you can also charge the pack with that.

To be able to fly and charge in same rate you need atleast 500W worth of solar or even more... When I fly i empty a battery within 3 minutes and that would equal to 400W continous if my math in my head isnt wrong. A sunny day thats 500W solar and cloudy its more like 4000W solar Smile
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcomming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#12
(09-09-2017, 07:11 AM)daromer Wrote: I fly quads too Smile

To charge above since you should not go below 80% you need around 1100 + some lossses. So if you need 10 chargs with you go with 15Ah atleast and so forth.

But if you going to charge the batteries skip the AC out... A proper RC charger works on DC and not AC. and if you have a cheap one only doing AC then buy a DC version. You can run it directly on the battery and you save both weight money and efficiency.

At home you run that charger on a Computer PSU or Server PSU is even better. Them you get for free and you can also charge the pack with that.

To be able to fly and charge in same rate you need atleast 500W worth of solar or even more... When I fly i empty a battery within 3 minutes and that would equal to 400W continous if my math in my head isnt wrong. A sunny day thats 500W solar and cloudy its more like 4000W solar Smile

Hi there,

I have a charger that works on dc and ac, so at home I plug it in the mains, on the field I want to use the DC plug. I don't want to use solar to charge the pack though.

I'll charge the powerpack at home, go to the field, fly, and recharge the pack at home.

Regards,

Ivo
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#13
Getting down to the process of buying material,  what do you guys suggest for the design of the battery pack?  I have a larger number of 18650 batteries around so don't need to buy them.  Are they kits any good?  (snap and use)

As for the rest I'm looking to start small with this one.

Solar panel and charge controller:
https://www.amazon.com/ECO-WORTHY-Volt-S...roller+kit

Inverter:
https://www.amazon.com/Power-Bright-PW90...++inverter

Looking to get ideas so the above are in no way carved in stone. 

-ck
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#14
These Vru**** kits are crap. I have one or two left over, but I will not sell them to you. You can get one for free and only have to pay the shipping costs, if you want and if it is worth the shipping. Depends on where you live.

How big will your pack be, how many cells in series and how many in parallel? Depending on the size of you pack a 20W panel is very small. You should not expect much. The inverter provides 900W, what are you going to power with it? It is a modified sine wave inverter, you can't power all devices with it and some only with reduced efficiency. And it is a 12V inverter, so I guess you are going 3S or 4S with your battery? Then you have the usual issue: 3S voltage is too low, 4S voltage is too high.
3S: Inverter will trigger its low voltage cut-off early without using the whole capacity of your, especially under heavy load or a spike.
4S: You can't charge your pack all the way up (about 3,87V per cell, depending upon exact specs of the inverter, I couldn't find any).
And also, if you are going to use all its power of 900W plus a bit more for its given efficiency you will need a battery pack that can provide a continuous output of about 90A. With reused laptop cells that will not be a small pack if you want to be safe and reasonable.
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#15
A 900W inverter need atleast 90 cells in paralell i would say ( To be very very generic) thats total of 3s90p. 270 cells in total.

V kits will NOT handle that current. Solar to that inverter if you want to be able to run it 100% out then you need atleast 2kW solar if you ask me Smile
Follow me! >> YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcomming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#16
I'm thinking solar as more of a trickle charger at this point.  Once I get the understanding of how these are setup I can upgrade to a 100% run on solar if there are no clouds.  :Smile

Downgrading the inverter to something like this:

https://www.amazon.com/Power-Bright-PW20...32&sr=8-32

Thoughts?  Can I wire that directly into the battery pack?  If you guys don't like vkits is there something out there you have used & liked?

Thanks!
-ck
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#17
Well, what I said in post #14 still applies. Before you made some basic decisions it doesn't make much sense to comment on the inverter.

The TLDR version:

1. What will you power with your inverter?
2. Modified sine wave, you are ok with that?
3. What will your battery configuration be like? How many cells in series and how many in parallel? 3S and 4S is both not that good for a 12V inverter.

For now I can say, just based on the comments on Amazon, that this inverter probably isn't a quality device.

And regarding your last question, sadly no. But I think we will get there some day since there is a demand for it. By the looks of it I like this one: http://18650.lt/
However, it gets stupendously expensive for a bigger pack and is only designed for 6P maximum. That can be changed of course, but won't make things cheaper. Rather the opposite. Looks good for smaller applications though.
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#18
Ok, more knowledge and I think we're getting closer to me having an understanding.

1. What will you power with your inverter?
**Small items.  Lights, fans,charging phones,etc.  Think camping gear.  
2. Modified sine wave, you are ok with that?
**After doing some refresher digging, I'd have to say full/pure sine.
3. What will your battery configuration be like? How many cells in series and how many in parallel? 3S and 4S is both not that good for a 12V inverter.
**3S5P will give me 11V,11000mah and 122.1Wh according to this calculator:  http://www.diypowerwalls.com/newreply.php?tid=2241

https://www.amazon.com/BESTEK-Power-Inve...e+inverter

^Claims to be a pure sine and looks like someone actually tested it.  Do you guys like clips or eyelets better?

-ck
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#19
Well, yes, 3S will give you 11.1V nomimal, 12.6V fully charged, 9.0V discharged. That is a bit low for a 12V system. 12V inverters usually don't work down to 9V, they don't even work down to 10V. My 12V inverter starts its low voltage warning at 11V and does an emergency cutoff at 10.2V. That makes sense because they are designed for lead acid batteries. The one you have chosen has a low voltage cutoff at 10V to 11V, whatever that means. Quite a gap there, but lets assume 11V worst case. So this inverter might turn itself off pretty close to the nominal voltage of you battery under load.

Imagine it like this: 3S battery fully charged, 12.6V. There is not much juice at the top end anyway so it will quickly be down to 12.0V anyway. Then there will be a load which causes the voltage to drop. Size of the drop depends on the load, with used cells and even a small load we could already be close to the cutoff voltage of the inverter. You are probably looking at minutes of operation with this setup before it stops working.

That's why 12V inverters on a 3S lithium battery are no joy usually. Also, inverters like this one at 300W will draw at least about 30A under full load, even more when the battery voltage is lower. With a 5P configuration that is at least 6A per cell which is too much for reclaimed 18650s. You should have a 30P battery at least in this case. With a 5P setup you shouldn't really connect more than 50W worth of devices to the output of the inverter.

So, 3S is no good, nor is 4S. 7S works well for a 24V system (or with a DC-DC converter for 12V). And you need a bigger battery to handle the current or keep an eye on the power draw of the devices you run on the inverter.
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#20
DarkRaven, thanks for the reply and breaking down the math for me. 

Switching to a 24v inverter and a 8s8p would be a better setup while still maintaining portability?

Possible inverter (but open to suggestions like always):
https://www.amazon.com/Go-Power-GP-SW300...00153CXVA/

Thanks!
-ck
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