Inverter/Charger dilemma

pfromero

Member
Joined
Jan 30, 2017
Messages
62
Hi all,

I am about to solder up my batteries, but I have (currently) only a choice of 4p, 8p, or 12p due to the restrictions of my battery holders (I bought 4x5 and 4x10 grids).


I have an exsting grid tie 240 VAC solar system, so I dont need a solar MPPT charger.

I looked at Outback Radian series inverter/chargers, and they told me "our inverters are not currently compatible with Li-ion cells unless they have their own BMS", adding $ to $$$.

I've looked at Aims Power and Sigineer Power charger/inverters (same exact design and well written manuals, but one is over double the price), and their charging voltage either will over charge or under charge the 4p, 8p or 12p packs I plan.

1) Does anyone use an AC charger/inverter with their 4p, 8p, or 12p battery packs? If so, could you suggest a manufacturer/model?

2) If I go with a BMS, does that allow me to have a different battery pack max voltage than my inverter/charger's max charging voltage? If so, could you suggest a manufacturer/model?

3) If you are using a different array count (example: 7p), how would I go about cutting my battery holders? Or, could you suggest an alternative?

Many thanks for your thoughts!

Paul


OOps,


It looks like Aspendell answered my 3rd question on another thread...THANK YOU!

Paul
 

LithiumSolar

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Oct 8, 2016
Messages
2,380
If the Outback Radian has the ability to set your own voltage, which is in the range of Lithium Ion cells, you can use it with your cells. That sounds like a general disclaimer to release them of liability if you use it without a BMS and something happens. Most of us are using similar chargers without any BMS. You really should have one but the availability and cost of BMS for the size battery banks we are building is unrealistic. There are a few guys there though building their own BMS that may be able to give you some pointers.
 

daromer

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Oct 8, 2016
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5,381
1. 4x5 or 4x10 is for me either 20p or 40p :) So i dont see the problem with limit you said. I use 80p in most of my setups but i also have plan for 14s22p setups. I dont use AC charger as such since my inverters will handle the voltage needed.
2. You should never use a standard BMS for sorting voltages or such. Thats always to be dealt with by the charge-source. A BMS is a system that can have some or all of below:
* Voltage monitoring
* Balancing(active or passive)
* Over voltage protection (Note the word protection, if this is hit it will shut of the inverter!)
* Under voltage protection (same here)
* over current protection (same here)
* Temperature protection and monitoring
* And in rare cases some more monitoring.

3. I suggest that you don't cut them and try to go with the size they are in. And if you want to split you can always split inside them instead for instance on a 20block you use 4s5p or whatever size you want on them.


You can set custom voltage and charge/discharge settings on almost all inverters. That's the main function needed to actually handle Lithium packs if you ask me.
Make sure you can disable float/bulk mode in the inverter since that type is not used on lithium!!

If those voltage limits is within the specification on the battery pack you are using its just go ahead and use it. The BMS is to make sure packs stay in balance and you in first case have individual protection on cell/pack basis since the inverter only monitors the full system!

Lead Acid batteries is a bit different where you balance by actually pulling them high. You don't do that on Lithium.

On some inverters you can also hook up the BMS to for disabling the inverter nicely if protection are needed due to any of above.


On a side note Im one of those guys building my own BMS. I'm constructing 2 systems in general
1. Bare monitoring system that monitors voltage and temperature and can control external stuff.
2. Full blown modular BMS system made for 14s. (Could potentially do 9-15s) This system will be a system that you can go all from monitoring to passive balancing to active and if you want add the protection circuits to disconnect.

Since a system like #2 in general cost up against 1000EUR..... I have as goal to have a system like theirs but to a 10th of that cost (hw cost that is)

If you are confident with building your own electronics there are some out there with designs already made up :)
https://libresolar.github.io/elements/bms-48v/
(There are more out there)

My #2 will be close to this system: http://www.autarctech.de/en/bms-balancer/

And if you only want balancing that do work and is active i have looked into this system: https://www.aliexpress.com/item/1S-...ce-equalizer-BMS-lithium-ion/32788338337.html (No im not affiliated with them)

I will be publishing a video of above 1s modular BMS tomorrow where i literally destroys a unit to see whats inside it :)


I hope i did answer some of your questions. Side note: p stands for parallel. a 4p pack will still be 3.7v nominal :) Meanwhile a 4s will be 4*3.7.

4s4p is 4in series of 4 in parallel. (I just added that as a FIY if someone reads it)
 

fprumbau

New member
Joined
May 27, 2017
Messages
8
Too late to go with the KickStarter project, I ordered one SBMS120 from his website directly. I'm very impressed with the project and already think of getting another one before they sell out (like the SBMS100).

Frank
 
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