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Using Victron MPPT to charge 7s18p 18650 set up.
#1
Planning a build at the moment in which I want to be able to charge from AC.

I have been trying to properly get my head around chargers to charge Lithium banks at high current, and it doesn't really seem like there are a huge amount of options.

I am toying with the idea of using a Victron bluesmart MPPT 100/30 to create a Lithium 'profile' and then feed the MPPT with DC via an AC-DC PSU.

So the setup would be:

AC240v to DC 60v20A to MPPT 100/30 to Battery bank.

This bank is a 29.4v charge, but as the Victron app focusses on Lead Acid batteries the terms they use do not relate and I'm having a little trouble figuring it out.

When you install the app without the hardware you can run a demo mode. The guide (found here) suggests you can set a 'bulk' voltage, which is what I would assume would be the setting you would need for a Lithium pack, however the actual app does not have this, it only has 'absorption' and 'float'...

Any references I find to using the MPPT to charge lithium online suggest you should set the bulk voltage, but this does not appear to be possible to me?

I am only experimenting with this idea at the moment, and my 'backup' plan is to purchase one of these from Omnicharge, they are not too expensive at £400/20A and £520/30A.

But I'm just trying to work my way through this idea as well to see what I think it best when it's all 'in place' in my mind.
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#2
Bulk is absorption and float is your well float voltage.

With Li-Ion  you want to set your absorption(bulk) to your max V you want the batteries to be charged at and float maybe 0.1V lower.

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#3
Ok, great, that is kinda what I was guessing but I didn't want to assume.

With the absorption (and 'equalization') voltage set to their lowest (18v) will the MPPT then follow a proper CCCV profile?
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#4
Sounds like algorithm number 7 needs to be enabled.
There should be no equalization on a Lithium battery.



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#5
Hmm, I don't see anywhere to set the 'algorithm' - there are presets but only one of them is for LiFePO4 and it does not remove the equalisation option.
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#6
There's a custom profile on my 150/60's.
I used that to set the float & equalize to the same as the bulk.
For my LiFePo4 batteries this is 3.41V/cell
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#7
If you choose LiFePo4 for the preset and then tweak the configuration from there the equalization option will be greyed out and non-selectable.Then you just have absorb and float. Whatever voltage you tell it to absorb at will be the top of the bulk setting and it switches from CC to CV and tapers off the absorption current as it reaches a full charge.
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#8
It would be better to bypass the mppt controller and instead use a buck converter, you can get a 30 amp buck converter for under 50 dollars.
The problem with mppt controllers is voltage surges if the bms on the battery activates, with buck converters it charges so slowly at the topend it be rare to activate the bms and if it does nothing happens.
With the mppt controller, you would have to set the bulk setting low enough so it never activates the bms, low bulk setting will result in the battery not receiving max amps.

These buck converters you can dial in the max voltage and max amps you want. You don't have to worry about equalization or float, as the battery gets full the amps drop. I use the smaller 20 amp buck converters to charge my 3s li-ion and 4s lifepo4 and even my agm lead acid, and it works excellent, better then any solar controller and more convienent then a balance charger. Having full control of the max volts and amps is a big plus in using these as chargers.

Install a 6 dollar LED 50 amp volt/amp meter and you can see the charge rate in realtime.


30a buck converter cc/cv with giant heatsink 20-70 volt in / 3-58 volt out


LED volt/amp meter
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#9
(06-11-2020, 01:37 AM)gpn Wrote: If you choose LiFePo4 for the preset and then tweak the configuration from there the equalization option will be greyed out and non-selectable.Then you just have absorb and float. Whatever voltage you tell it to absorb at will be the top of the bulk setting and it switches from CC to CV and tapers off the absorption current as it reaches a full charge.
Thanks for confirming that, thats basically the info I was after!

The demo doesn't grey it out so must be something that happens in the main app.

(06-11-2020, 02:52 AM)jonyjoe505 Wrote: It would be better to bypass the mppt controller and instead use a buck converter, you can get a 30 amp buck converter for under 50 dollars.
The problem with mppt controllers is voltage surges if the bms on the battery activates, with buck converters it charges so slowly at the topend it be rare to activate the bms and if it does nothing happens.
With the mppt controller, you would have to set the bulk setting low enough so it never activates the bms, low bulk setting will result in the battery not receiving max amps.

These buck converters you can dial in the max voltage and max amps you want. You don't have to worry about equalization or float, as the battery gets full the amps drop. I use the smaller 20 amp buck converters to charge my 3s li-ion and 4s lifepo4 and even my agm lead acid, and it works excellent, better then any solar controller and more convienent then a balance charger. Having full control of the max volts and amps is a big plus in using these as chargers.

Install a 6 dollar LED 50 amp volt/amp meter and you can see the charge rate in realtime.


30a buck converter cc/cv with giant heatsink 20-70 volt in / 3-58 volt out


LED volt/amp meter

I actually have a few DPS5020 programmable bucks on the way for a separate part of the project (I'll be supplying various electronic equipment from this battery). I was wondering if this was the case but I think the issue is that I want to be able to 'set and forget' these batteries. So when they reach 100% SoC they disconnect themselves from the charger and are not constantly being trickled a current. Can this last part be entirely handled by the BMS? (Tiny BMS) (I'll take a closer look at the manual today)
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#10
Right, after reading through the TinyBMS manual, it seems like this should work without issue and I also think I understand the whole process a little better.

I am going to write out the process as I understand it, which I believe I have correct:

1. Connect battery. PSU/buck supplies 30A continuous by regulating the voltage
2. Battery reaches 4.2V, as the battery no longer drawing max current from the buck the buck instead maintains voltage
3. The current draw from the battery tails off as it reaches 100% SoC
4. As current drops below 'X' (ad defined by BMS) the BMS 'switches off' the charging circuit, only switching it back on if the battery is disconnected then reconnected.

So there is never any risk of over charge because the BMS switches off the circuit. Should you plug the battery back in it will restart this process, almost immediately reach 100% SoC and less than the predefined min charge current and turn off again.
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