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18650 trolling battery solar charging
#1
Ok so have some questions on charging a battery pack built with 18650 cell. So basically the background of what im doing is every other year or so we go up camping up to MN up near ELY. Its a big camping/fishing trip. It is all canoe fishing, and a few years ago I put a small trolling motor on my canoe, which works great. But the 100ah battery im using is super heavy and just doesn't last. The place where we stay does not have any electricity. So in the past I have just pulled out the battery and put jumper cables on it from my running truck to charge it back up.

Now I want to change my set up for a couple of reasons. Some times we have to do small portages (carrying the canoe across land from one lake to another) and that huge lead acid battery is super heavy. And I also want another option for charging. So I'm in the process of making some battery packs out of 18650 cells. And I was going to charge them using 200W solar

The charge controller is a Renogy Wanderer 10 Amp 12V/24V PWM Negative Ground Solar Charge Controller
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

the solar panels Im using is 4 -50W flexible panels

https://www.ebay.com/itm/353095224156

So I was thinking of making 2 smaller battery packs rather then having just 1 big one like i had before, so 2 that are around 50ah ea, that way one will be on the solar charging up all day while the other is being used.

My old lead acid was a walmart "deep cycle" battery that was rated at 105ah and I could get around 2 ish days of use out of it before it would drop down to around 12.00V which is ballpark around 50% drained and everything I have heard is to make them last dont discharge below 50%

So one of my questions is in the AH rating of the different batteries. Is that 105ah battery rated for safe usable power? like the 105ah is based on only a 50% discharge rate? or is the 105ah based on completely draining the battery?

So I know that Lithium Ion has a much high % of usable power so im trying to get a ballpark number of cells to use to get comparable same "2 days of use"

Which brings me to my next question 12.6v or 16.8v? I have seen a lot of people building trolling motors using 4 in series rather then 3 to get 16.8v. a 18650 fully charged is 4.2v while drained is around 3v. So if i build it in 3 in series that gives me a 12.6v battery which sounds perfect. But drained im looking at 9v so not sure at what point the lower voltage will not work with the trolling motor. Which is why i have heard of people using 4 in series to get 16.8v down to a 12v drained battery. 

So I was leaning towards the 4 in series to get the 16.8 volts, but what about charging that high with my solar set up? 

So I guess I have rambled long enough, tell me what your thoughts are and thanks in advance for any help.
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#2
A 105 ah lead acid is rated 105ah if discharged over 20 hours. But thats only for high quality deep discharged batteries that can actually handle that type of use. Like the odyssey agm's (very expensive) they can handle being drained below 12 volts many times before they lose capacity. The cheaper lead batteries its best not to go below 12 volts.

For your situation I recommend the 3s li-ion, that will charge extremely well with solar. The voltage differential is great enough that you get a good charge. In my situation with a 240 watt panel and mppt controller I was getting up to 15 amps into my 3s li-ion battery. With lead acid and a 4s lifepo4 I only get about 12 amps from the same panel. I saw peaks of 17 amps every once in a while (which was close to 244 watts from reading the mppt controller lcd screen).

With a 4s li-ion, you need more than 16.8 volts bulk setting to charge, closer to 18 volts, you have to have a big voltage differential to fast charge. If its too close to the 16.8 volts, your controller won't put out too many amps. You need to check to see if your controller bulk voltage can be set high enough for a 4s. Don't use the lithium setting if it has one, it will charge too slow. With solar you need the bulk voltage setting high enough to quickly charge while the sun is out.

Since you will be charging with solar I recommend the chargery bms8t bms, its the only bms I trust with solar. Especially if you plan to fast charge the battery. This way you can set the bulk setting on your controller high enough to quickly charge the battery. If you want to see the status of your battery while charging its the bms to get, fully programmable, balances at 1.2 amps and has audio alarms, temps sensors.

As far as capacity, a li-ion battery can  be drained all the way until the bms shutsoff. So a 50ah li-ion would be comparable to a 100ah lead acid, except the voltage will be lower as it gets drained but still usable if your equipment can operate at those voltages. If you drain less it will last longer but fully draining everytime will still outlast any lead acid even the odessey.
dbldrew likes this post
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#3
I would add that 4 x 50w = 200w of solar panels.   200w/12v = 16.6 amps.   Even if you're only doing 75% of 200w, that's still 150w/12v = 12.5a - a bit above the 10a max in the charge controller you list. 

The practical range of 18650 is 4.15v high and 3.3v low.
For 3s, that's 12.5v high and 9.9v low
For 4s, that's 16.6v high and 13.2v low

The trolling motor would probably operate stronger on 4s...   but 16.6v high is higher than nominal (typical) 12v batteries and a 12v charge controller may not work that high.  That's probably one of the reasons @jonyjoe505 recommended 3s.    The remedy is to make sure you get a programmable 12/24v charge controller - where you can custom set the high of 16.6-16.8v for 4s OR 12.5v for 3s as neither of these are not quite normal for 12v.

Another angle is to go LifePO4 instead of 18650 - and then 4s will match lead-acid 12v voltage ranges. 

I'm sure others will add comments - sounds like a fun project Smile
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#4
thanks for the heads up on the charge controller, canceled that and now will look for a better option. What if i ditch the charge controller all together? Is there a good bms that can handle the charging and I connect the solar panels directly into the bms? The panels are listed as 18v so maybe a 4s would work in that situation? Or is that not a good idea?
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#5
(06-05-2020, 03:04 AM)jonyjoe505 Wrote: As far as capacity, a li-ion battery can  be drained all the way until the bms shutsoff. So a 50ah li-ion would be comparable to a 100ah lead acid, except the voltage will be lower as it gets drained but still usable if your equipment can operate at those voltages. If you drain less it will last longer but fully draining everytime will still outlast any lead acid even the odessey.

This was my worry, how well will it work when the voltage drops under 11v. Which is why everyone i have seen that has made trolling batteries have all done 4s. Which is why i was leaning that way but then the problem comes with charging. have to try and find a charge controller (thats not crazy $$) that I can adjust the charging voltage, unless having the solar straight into the BMS is an option
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#6
(06-05-2020, 11:51 AM)dbldrew Wrote: thanks for the heads up on the charge controller, canceled that and now will look for a better option. What if i ditch the charge controller all together? Is there a good bms that can handle the charging and I connect the solar panels directly into the bms? The panels are listed as 18v so maybe a 4s would work in that situation? Or is that not a good idea?
Not a good idea to try to charge Lithium-ion directly from panels.   The top voltage must be regulated to ensure it doesn't go above 4.2v/cell or you're at risk of fire.     For 3s/4s 18650 - you need a charge controller where you can set the top charging volts yourself - in the 12/24v range.

The one I started with (which is fully programmible) is this - https://www.amazon.com/Controller-Negati...52&sr=8-14

Another one that is cheaper, fully programmable is the famous MPT-7210a  (many youtubes on this).  Its limited to 10a on output but is fully programmable - and you could do 2 in parallel if you like the 1st one.    https://www.ebay.com/itm/LCD-MPT-7210A-M...Swe9tepqNQ

Perhaps someone can recommend a cheap 20a/24v they know is programmable.   

P.S. A BMS is for battery safety (shut it off if v is too high/low,  temp to hi/low) and many add a balancing feature... and is recommended!.   But they don't include charging.
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#7
(06-05-2020, 03:53 PM)OffGridInTheCity Wrote:
(06-05-2020, 11:51 AM)dbldrew Wrote: thanks for the heads up on the charge controller, canceled that and now will look for a better option. What if i ditch the charge controller all together? Is there a good bms that can handle the charging and I connect the solar panels directly into the bms? The panels are listed as 18v so maybe a 4s would work in that situation? Or is that not a good idea?
Not a good idea to try to charge Lithium-ion directly from panels.   The top voltage must be regulated to ensure it doesn't go above 4.2v/cell or you're at risk of fire.     For 3s/4s 18650 - you need a charge controller where you can set the top charging volts yourself - in the 12/24v range.

The one I started with (which is fully programmible) is this - https://www.amazon.com/Controller-Negati...52&sr=8-14

Another one that is cheaper, fully programmable is the famous MPT-7210a  (many youtubes on this).  Its limited to 10a on output but is fully programmable - and you could do 2 in parallel if you like the 1st one.    https://www.ebay.com/itm/LCD-MPT-7210A-M...Swe9tepqNQ

Perhaps someone can recommend a cheap 20a/24v they know is programmable.   

P.S. A BMS is for battery safety (shut it off if v is too high/low,  temp to hi/low) and many add a balancing feature... and is recommended!.   But they don't include charging.

if i get the MPT-7210a would there be any issue with running the 4 - 50W panels that could produce more amps then the output of the controller? Or is it just not getting the full potential of the panels?
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#8
(06-05-2020, 05:25 PM)dbldrew Wrote: if i get the MPT-7210a would there be any issue with running the 4 - 50W panels that could produce more amps then the output of the controller? Or is it just not getting the full potential of the panels
According to this listing (  https://sightsolar.com/product/lcd-displ...ontroller/  ) of features....
 "Overload protection: the controller will automatically cut off circuit if overload."

So it sounds like it would just not produce any power - in which case you could re-configure to use 3 panels instead of 4.    The thing is - if its shady or cloudy or angle is not great it will reduce the power of the 4 panels and may not be an issue.    

You can experiment a bit with panels - just hook them up into dead-short and use a clamp (amp) meter to measure the amps as you position them - flat or at an angle etc - and get an idea of how 4 will behave, then try 3 etc.  
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#9
I would use a Victron Smart MPPT for a charge controller
I would use a DC-DC converter or a RC balance charger to charge from the cars 12v system

Personally I think mobile solar is a lot of work, bulky, and inconvenient ... I rather just have a storage battery in the truck (like a Tesla EV module), so I can charge the trolling motor battery a couple times from an RC charger. Its going to be WAY faster than waiting for some solar panels.

The storage battery in the truck can be charged/replenished from a small solar setup, and from alternator when the truck is running. This way you dont have to worry about where the trolling motor battery is, or what its doing. I have a small setup in my truck I operate in a similar manner to run a ARB fridge when I camp.
Doin it likes this post
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#10
(06-05-2020, 05:25 PM)dbldrew Wrote:
(06-05-2020, 03:53 PM)OffGridInTheCity Wrote: Another one that is cheaper, fully programmable is the famous MPT-7210a  (many youtubes on this).  Its limited to 10a on output but is fully programmable - and you could do 2 in parallel if you like the 1st one.    https://www.ebay.com/itm/LCD-MPT-7210A-M...Swe9tepqNQ

if i get the MPT-7210a would there be any issue with running the 4 - 50W panels that could produce more amps then the output of the controller? Or is it just not getting the full potential of the panels?
The mpt-7210 can't charge a 3s or a 4s battery really not usable until 7s. Perhaps I missed it Did the battery change from 3s/4s to7 s? The voltage of the solar panels has to be lower than the voltage of the battery.
 later floyd
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