Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: nowty on February 13, 2018, 11:23:36 PM



Title: Mixing Lithium and Lead
Post by: nowty on February 13, 2018, 11:23:36 PM
Last year I bought several cheap second hand Growatts with 5 kWh batteries off fleebay, one of which I had been keeping as a spare. But my experience is once you buy a spare item, it never gets used so I started thinking of uses for it. The battery cannot be used without the Growatt controller as its operation is locked down. I was a bit bored the other day so decided to take the back off the battery and have a closer look to see if it could be easily unlocked. tumble:

(https://s5.postimg.cc/zeb5q896v/Growatt_Battery_002.jpg) (https://postimages.org/)

It contains 14 battery modules in series and a proprietary protection circuit board. Each battery module contains 18 of 5,300 mAh cells in parallel so a total of 252 cells. Each cell is apparently two 18650’s in parallel in a single package. :o

http://liionbms.com/pdf/bostonpower/swing5300.pdf

First thing was to rip out the protection board and then the two battery racks conveniently come out to give 24v each. Then I had a crazy idea, my Sunny Island runs at 24v using forklift cells. Would it be possible to add them in parallel to increase my OffGrid capacity ? wackoold

It sounded like an absurd idea, mix lithium and lead ?, but the more I thought about it, the more it started to be a possibility. Charge and discharge graphs are different, but my operating range of lead is typically between 100% and 75% SOC. Voltage wise, this matches favourably with lithium between 100% and 40% SOC. Although I would only be adding circa 20% more Ah capacity, the actual usable capacity might increase by 50% or more. At high SOC, the lithium ones would provide most of the power so may extend the life of my forklift cells which are now 6 years old.

I took out the two lithium racks and connected them in parallel with my forklift cells when the voltages were roughly equal to prevent any initial current surges. :crossed

(https://s5.postimg.org/bake1xj07/Growatt_Battery_001.jpg) (https://postimages.org/)

(https://s5.postimg.org/c1d48763b/Off_Grid_-_Batteries.jpg) (https://postimages.org/)

Then I reduced the charging voltage of my Sunny Island from the current 30.5v to 29.4v and set the temp compensation to zero. 29.4v gives the max 4.2v charging voltage per lithium module and is still good enough for the forklift cells. bike:

Next day was full sun chocpot:, so I measured the voltage of each lithium module regularly. Voltage increased more slowly than just with lead alone and the lithium was taking 75% of the current. When the voltage rose to around 28v the current was shared equally, then over 29v the lead was taking most of the current. The voltage of each lithium module was identical except for one with was 0.1v more, so cells looks nicely balanced so far. When the charging day was over at 29v, the lithium then discharged slightly and continued to charge the lead until the voltages stabilised at around 27v so continued the absorption charge of the lead even after the sun went down. ;D

On discharge, from 27v down to 26v the lithium was supplying almost all the load.
From 26v down to 25v, the lead started to supply some of the load.
At 25v lithium and lead were supplying exactly half and then the voltage hardly moved down to 24.5v by the morning.

My first result is encouraging, no dramas sh*tfan:, definite increase in capacity, better voltage stabilisation on discharge and batteries accepted the max charge from the Sunny Island all the time without throttling back. This is an advantage I had not even thought of. ralph:

Going forward I need to sort out some sort of protection circuit for the lithium as I cannot risk leaving it day after day charging the lithium to near 100%. :norfolk

Watch this space     …………………………..........


Title: Re: Mixing Lithium and Lead
Post by: rogeriko on February 13, 2018, 11:40:32 PM
There's hundreds on fleabay https://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=li-ion+protection+7s


Title: Re: Mixing Lithium and Lead
Post by: knighty on February 14, 2018, 02:07:27 AM
if you search for BMS it will give you a lot of options

there's a hell of a lot to chose from... most will just monitor the cells and dump power into resistors (making heat) to discharge any cells which are over discharging

but... you can get fancy ones which will dump power from high cells into low cells


if you parallel up the balance wires, then you'll only need one BMS for the whole lot :-)


Title: Re: Mixing Lithium and Lead
Post by: linesrg on February 14, 2018, 09:08:18 AM
nowty,

Now I know what the inside of my battery looks like!!!

I can see it wouldn't be that difficult to re-wire things internally to allow the cells to be charged by an external power supply. As I may have noted elsewhere simply connecting the positive and negative leads from the Growatt battery to a charger does nothing as the circuitry obviously needs a signal from the Growatt SP2000 unit.

I some very heavy duty (Albright) DPDT solenoids which can be used for this.

Regards

Richard


Title: Re: Mixing Lithium and Lead
Post by: biff on February 14, 2018, 09:15:10 AM
Wow,
    Exciting stuff Nowty,  I wonder what it would take to put together a 120volt bank, ?
   Could I chain a series of Growatts together, ?
                                       Biff
    I guess the thing to do would be to study the suitable BMSs first and then try and find the way to keep them happy.
 I could sell my Lead acid friends.. :genuflect


Title: Re: Mixing Lithium and Lead
Post by: Westie on February 14, 2018, 09:48:25 AM
Assuming the SI is set for charging LA batts  SI will trickle charge as is normal for LA,  so isn't there a danger of overcharging the Li batteries during trickle charging?

I would be thinking about protecting against fault current flowing between banks  by adding a fuse between them?

Would be nice to get a schematic of the Growatt BMS, if the 'authorisation' handshake could be faked the BMS would probably still operate.




Title: Re: Mixing Lithium and Lead
Post by: Fionn on February 14, 2018, 10:04:10 AM
Would it not make more sense to connect the pack in parallel with one of your existing growatt units, even if at the module level?

If you're looking for a cheap but useful BMS, this one is worth a look:
https://www.aliexpress.com/item/14S-Smart-Li-ion-Battery-PCB-board-Bluetooth-Mobile-BMS-for-48V-58-8VLi-Ion/32794186005.html

The majority of the ones on eBay have no adjustability on their settings so you can't vary the over voltage and under voltage limits.

Was there any fusing between the parallel packs in each module out of interest?

If you held onto the existing BMS it might be of interest to someone with a bare Growatt and other batteries.


Title: Re: Mixing Lithium and Lead
Post by: nowty on February 23, 2018, 09:38:51 PM
Project Updates,

Lined the shed with cement board to prevent the odd fire mishap. It won’t survive a full-on lithium fire, but it will mitigate against scorching by blown fuses, loose connections, etc. :crossed

Added an isolator.

Added fuses for each parallel battery string. :crossed

Picked up another cheap Growatt, so I now have four battery strings. exhappy:
(https://s5.postimg.cc/tiu35l2t3/Offgrid_Lithium.jpg) (https://postimages.org/)



Added a DC isolator to the lead batteries so I can just run off the lithium if I want to. In fact, in future, I am thinking of only running on lithium during the winter months. tumble:
(https://s5.postimg.cc/wcx8j0htz/Battery_Isolator.jpg) (https://postimages.org/)


I have been manually balancing the batteries by,

Using a 50w resister to reduce down any high cells. I found one cell which was 0.2v too high and bled it off for a couple of hours with a 1 ohm resistor. :ballspin
(https://s5.postimg.cc/kies8xbkn/Battery_Discharger.jpg) (https://postimg.cc/image/gysuj48ur/)

Using a bench low voltage supply to charge up any low cells, I found one which was 0.4v too low. Five hours of individual charging brought it back up in line with the others. :fume
(https://s5.postimg.cc/fp5qgi7mv/Battery_Charger.jpg) (https://postimages.org/)


Apart from those two cells all other cells were found to be within 0.05v of each other and all are now  keeping balanced after several charge / discharge cycles. :cross


I have been manually isolating the lithium when the bank voltage hits around 28v (cell voltages of 3.8v and 80% SOC), and then continuing the charge on the lead up to 30v. At the end of the charging day I reconnect the lithium bank.
I have ordered a heavy duty normally closed DC contactor relay which will be opened and closed by a voltage sensing relay to perform this task automatically. whistle


Title: Re: Mixing Lithium and Lead
Post by: biff on February 23, 2018, 10:48:34 PM
Wow Nowty,
         I am green wif impreszions. You have some crazy good gear. Yours is the battery thread of the century. Real porn.
       Biff


Title: Re: Mixing Lithium and Lead
Post by: knighty on February 23, 2018, 11:25:00 PM
you should really parallel up each cell in the packs

you could just join the balance connectors ?

should really have a fuse on each one too!


advantage is if one cell pack is a bit weak it should average out a bit with the others :-)


Title: Re: Mixing Lithium and Lead
Post by: nowty on February 24, 2018, 05:18:04 PM
you should really parallel up each cell in the packs

you could just join the balance connectors ?

should really have a fuse on each one too!


advantage is if one cell pack is a bit weak it should average out a bit with the others :-)

I actually did this with the first two strings, i.e. connect the balance connectors together via pin headers, but I was concerned that I would inadvertently short one out so I cut them off. facepalm

I am experimenting using some cheap crop clip test leads to parallel up in a couple of places to improve the balancing but I was only going to do this temporarily, then monitor cells over a long time to see how much the cells  drift. I agree that permanent linking should require fuses.
(https://s5.postimg.cc/cgnxhtvnb/Parallel_up_Cells.jpg) (https://postimages.org/)




And today my heavy duty DC relay arrived but I am still waiting for the voltage sensing relay to wing its way from China.
(https://s5.postimg.org/knt8v26av/Heavy_Duty_DC_Relay.jpg) (https://postimages.org/)


Title: Re: Mixing Lithium and Lead
Post by: fourfootfarm on February 26, 2018, 07:47:14 PM
Croc clips pretty much are fuses!

Really interesting stuff will be keeping this in mind for future upgrading


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 05, 2018, 03:30:30 PM
Picked up another two Growatts which were sold with red lights on the battery pack so were cheaper than usual. Batteries were fine, one had a low cell which needed some individual charging and the other had batteries down to 10% SOC so just needed charging up a bit. I think I might do away with my lead acid and just run on the lithium. tumble:


Other changes,
Upgraded the isolator as the original one was running a little hot. :fume

Added the isolating relay and tested it at a charge rate of 80 Amps. I was surprised as it did not even spark when breaking the connection. :o
But I am still waiting for my voltage sensing relay from China, so i am still having to disconnect the lithium manually. facepalm

I am currently making up some fused battery links to connect all the cells together. bike:

(https://s5.postimg.org/e0nsmut5j/Growatt_Battery_005.jpg) (https://postimages.org/)


Title: Re: Mixing Lithium and Lead
Post by: knighty on March 06, 2018, 06:25:22 PM
how big is your lead acid pack?

20kwh of LiIon is quite a bit?


how's the usable kwh or LiIon vs lead acid compare?


Title: Re: Mixing Lithium and Lead
Post by: biff on March 06, 2018, 07:01:51 PM
Neat work Nowty,
                        Biff


Title: Re: Mixing Lithium and Lead
Post by: Nickel2 on March 06, 2018, 07:03:44 PM
I'm starting to develop lithium envy! :genuflect


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 11, 2018, 04:44:13 PM
My voltage sensing relay finally arrived from China.

Its now installed so I have set the Sunny Island back to Lead Acid charging voltages and can happily leave it unattended.

(https://s5.postimg.cc/44zmdayg7/Growatt_Battery_006.jpg) (https://postimages.org/)


Title: Re: Mixing Lithium and Lead
Post by: peterboat on March 11, 2018, 05:48:40 PM
My voltage sensing relay finally arrived from China.

Its now installed so I have set the Sunny Back to Lead Acid charging voltages and can happily leave it unattended.

(https://s5.postimg.org/44zmdayg7/Growatt_Battery_006.jpg) (https://postimages.org/)
This is what I am doing with my Valence batteries could you provide links for the voltage sensing relay and the heavy duty disconnect please as long as you are happy with the quality and operation that is
Peter


Title: Re: Mixing Lithium and Lead
Post by: biff on March 11, 2018, 06:23:31 PM
Great thread Nowty,
        I wonder to they do the 120v version,?  Must have a look and see if i can find a similar set up, At least I know what it looks like now, :crossed
                                                                          Biff


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 11, 2018, 06:43:02 PM
This is what I am doing with my Valence batteries could you provide links for the voltage sensing relay and the heavy duty disconnect please as long as you are happy with the quality and operation that is
Peter

Yes I am happy with it, I tested the DC relay at 80amps and it did not even spark. I tested the voltage sensing relay with a variable power supply and it works as I want it to.

Voltage sensing relay,
https://www.ebay.co.uk/itm/DVM-A-DC24V-DC-over-voltage-protection-relay/232540318361?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

I also bought one of these (digital version of a voltage sensing relay) as an alternative,
https://www.ebay.co.uk/itm/Battery-Charge-Discharge-Board-Under-Over-Voltage-Protection-Module-DC-6-40V-DE/322885829605?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Heavy Duty (normally closed) DC Relay
https://www.intellitecmv.com/collections/relays/products/relay-spst-normally-closed-24v-150a


Title: Re: Mixing Lithium and Lead
Post by: Tinbum on March 11, 2018, 10:50:11 PM
Cheaper here;
https://www.aliexpress.com/item/1X-Free-Shipping-DVM-A-DC-Over-Voltage-and-Under-Voltage-Protection-Relay-With-Socket/1074413909.html?ws_ab_test=searchweb0_0,searchweb201602_5_10152_10151_10065_10344_10130_10068_10324_10342_10547_10325_10343_10340_10548_10341_10192_10190_10084_10083_10618_10307_10301_10303_10313_10059_10184_10534_100031_10103_10627_10626_10624_10623_10622_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=d12c7025-daba-47bc-b2b1-69d6d04049c1-0&algo_pvid=d12c7025-daba-47bc-b2b1-69d6d04049c1&priceBeautifyAB=0

Biff they only seem to do the 4 different voltages.


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 12, 2018, 10:30:08 AM
And another slightly more compact version made by the same company.

https://www.aliexpress.com/store/product/DVRD-DC-Over-and-Under-Voltage-Relay/1916063_32826508821.html?spm=2114.10010108.1000023.1.4aadba4d0aaQDh

http://en.ginri.com/products-mpid28.html


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 22, 2018, 11:23:46 AM
Installed fused links to interconnect all the cell modules and I can confirm that the DC breaker and voltage sensing relay are working in real life conditions.

I was hoping for the increased capacity to give me two days autonomy as we rarely get more than two consecutive poor solar days between mid Feb to end of Oct. But after being fully charged I managed to get through three really poor days with the recent snow. And just two more good days to fully charge again.

I seem to have around 20 kWh’s of real life useable storage which is a great increase from 5kWh’s just relying on the lead acid.

(https://s5.postimg.cc/uc7afwolj/Growatt_Battery_007.jpg) (https://postimages.org/)


Title: Re: Mixing Lithium and Lead
Post by: knighty on March 22, 2018, 01:43:34 PM
that's looking really good/tidy - nice job there :-)


it's nice to see LiIon available for DIY stuff without costing megabucks - hopefully it's a sign of good things to come


I'm not 100% sure I'm right... but I think even a half knackered liion pack is still just as efficient as a brand new one - it just has less capacity?
(where lead acid has higher standing/charing losses etc. ?)


Title: Re: Mixing Lithium and Lead
Post by: nowty on March 22, 2018, 05:28:09 PM
I'm not 100% sure I'm right... but I think even a half knackered liion pack is still just as efficient as a brand new one - it just has less capacity?
(where lead acid has higher standing/charing losses etc. ?)

Yeah, I think thats right.

I have noticed that as my lead pack is now only slightly charging / discharging compared with the lithium pack, its temperature has dropped to almost ambient.

The lead used to run nearly 10 degrees hotter which just shows the inefficiency of them.


Title: Re: Mixing Lithium and Lead
Post by: nowty on April 21, 2018, 06:58:53 PM
Latest and probably my last update on this project, not likely to be any more changes now.
Its working as well as I could have expected, very happy with it. :crossed


Added permanent voltage displays on each parallel cell so I don't have to use my multimeter any more and can see immediately if there is any voltage imbalance. tumble:
(https://s5.postimg.cc/erolvivyf/Growatt_Battery_008.jpg) (https://postimages.org/)


Added permanent charging current meter and voltage meters for both Lead and Lithium batteries. :ballspin
(https://s5.postimg.cc/avb9zjion/Growatt_Battery_011.jpg) (https://postimages.org/)


Final Picture ralph:
(https://s5.postimg.cc/ymanhnqlj/Growatt_Battery_012.jpg) (https://postimages.org/)


Title: Re: Mixing Lithium and Lead
Post by: biff on April 21, 2018, 10:12:47 PM
Dam,s impressive Nowty,
                      It is a lovely set up.
                                       Biff