What charger for Lifepo4 and Daly BMS

gregster

Neues Mitglied
07.05.2021
17
Hi everyone,

I am struggling to identify what charger to buy to charge my 36V Lifepo4 batteries...

My questions are:
- Would a 42V charger be sufficient?
- Would I need to buy a charger specific for Lifepo4? As I will be charging through the Daly, does it make any difference?
- Amperage wise, would 30A be optimal? If I go lower, like 10A, would charging time be really long?

Thanks a lot for your input! Here is the current setup:

- 12 x 3.2V 105Ah lifepo4 in series with the specicifities mentioned below
- Connected via Daly BMS 12S 36V 200A
- To run a 36V 2.5KW motor

 

Kamikaze

Aktives Mitglied
As I have almost the same setup (although mine is 12S2P), maybe I can help a little.

42V Charging-Voltage should be enough. That means each Cell ist provided with 3,5V which should equal about 95% full. The charger I plan to use for overnight charging will use only 40,7V which should get the Batteries around 80% full (which is said to be near the optimum for battery-life).
My old charger cuts off at 43,5V. I will keep that for topping off the Batteries before really long drives. But being kept at that voltage for prolonged periods (i.e. every night) will significantly harm the batteries in the long run.

The old charger (the one with the high cutoff-Voltage) I bought there: https://www.akkukaufhaus.de/ladeger...10a-lifepo4-ladegeraet-fuer-life-akkus?c=3769
But I must warn you: I just recently discovered, that this charger will rise the charging-voltage even above 43,5V to keep the charging current up right until the cutoff happens. And the charging resumes as the batteries drop below 43,2V until the batteries are above 43,5V again. So this charger will fill the Batteries to 100% SOC, which will damage the batteries in the long run, but it is still handy a few times each year - be it for long-haul trips or allowing for top-balancing to be done.

The new chargers I got from @Martin Heinrich , which are basically just Power supply units for electronics, can be adjusted in the maximum current and the voltage.
As soon as I can trick the BMS of my EL to monitor the charging with these, I will use one daily with a Voltage-setting to about 40,7V. This should optimize battery life. The maximum achievable current is about 20A, but that drops to around 2-3A when the batteries are full. It will not become 0A ever. That is just how LiFePo4-batteries work.
Anyway - the current will decrease significantly as the Batteries gradually fill up. That's why I turned up the voltages of the ones I intend to use as a quick-charge option for long-haul trips to keep up a high charging-current for longer. There should be no harm in that bechause on these trips I presumably hardly ever will have enough time and patience to risk overcharging the batteries. (Just to be sure they will not exceed 43,5V. I quite like my batteries and don't want them to die early.)

If you use a CHARGER - make sure that it is suitable for LiFePo4-batteries!
Chargers for other chemical compounds might likely damage your cells by using wrong charging-patterns.
If you use "dumb" power-supply units make sure they are set to the right voltage and are capable of limiting their output-current. Otherwise you might damage your cells or the unit.
The charging-pattern for LiFePo4 is CCCV (constant current - constant voltage). That means the charger has to limit the charging current as long as the batteries will consume so much power to not allow it to come up to its voltage-setting, but as soon as the voltage can be met that has to be maintained while the charging-current gradually decreases.

Keep in mind that the EL will allow for battery-currents above 100A, so you are able to put significant strain on your cells. That means you should maintain a steady temperature for those. Putting them under that much stress at freezing temperatures might damage them which leads to premature degradation. Keep them above 5°C - better 15°C but under 45°C - better 35°C for getting the most lifetime out of them. (Cycles are not that important. Those are most likely never met in the battery's lifetime anyways.)

Hope that helps. :)
 
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gregster

Neues Mitglied
07.05.2021
17
Hi Kamikaze,

This is not the first you are helping me on this forum! Thanks so much. This is indeed most useful.

I think that I may actually order the old charger, even it does have some issues with max charge, it seems that it may be a really good option for me https://www.akkukaufhaus.de/ladeger...10a-lifepo4-ladegeraet-fuer-life-akkus?c=3769

I see that the connection is not compatible right for my city. I suppose that I just need to strip it, and put the connecitons for the +ve and -Ve, and then connect to the Daly (-ve) and to the main +ve on the batteries?

Could you please confirm?

Thanks again,

Greg
 
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Emil

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04.04.2006
2.692
Please be aware that the Daly BMS has only a minor balancing capability, and it balances only when charging.

Please look at the Andys offgrid garage for more information.

There are more than one video.

If one cells hits the maximum voltage it turns charging MOS-FETs off. At this moment there is no further balancing, until the voltage drops a bit and the charging MOS-FETs are turned on again.

So I would add an additional external active balancer, or passive top balancers that are able to bleed more current away.

I would stay at a maximum of 3,50 V/cell, as with a charge current of 10 A only, the cells are full at this voltage. A charger that allows adjustment of charge voltage would be best.

And keep in mind that you should charge all the cells in parallel to 3,60 V/cell at least, and keep them in parallel for a few days, before you connect them in series. This balances all cells perfectly and avoids long balancing on first use.
 
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Kamikaze

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I see that the connection is not compatible right for my city. I suppose that I just need to strip it, and put the connecitons for the +ve and -Ve, and then connect to the Daly (-ve) and to the main +ve on the batteries?
That is exactly how I did it.
(Although I'm not familiar with the cabeling of the Daly-BMS in particular. I'm using a Boostech-BMS.)
This Charger is small enough to be mounted under the seat and a connector-piece is included for using the charger with the attaced plug. I made a hole in the underseat-plate and fitted the connector there so I was able to test the charger a few weeks before I strapped it under the seat.
For that I had to strip the cable and cut off the plug as the cable is way too long to be feasible for underseat-usage, but I wanted to test it beforehand for garantee-reasons.

As Emil said the initial balacing is important and if the Daly really is that weak in top-balancing, then an additional top-balancer (passive) is the way to go. (Personally I don't like active balancers, but others here seem to use them successfully.)
Sadly the cutoff-voltage is quite high and can not be adjusted with that charger - that's why I bought some which can be adjusted. Maybe an additional Cell can mitigate that. (So 13S instead of 12S, if your BMS supports that.)
 
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Emil

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04.04.2006
2.692
You may also use a "42 V" charger indented for 10s Li-on battery packs. 42 V / 3,5 V/Zell match 12s LiFePO4 packs.
 
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