Charge both lead and Lifepo4 batteries at the same time

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xtaille@free.fr
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Charge both lead and Lifepo4 batteries at the same time




by xtaille@free.fr » 08/11/18, 13:03

Bonjour à tous
In my sailboat I have 3 groups of batteries:
-a battery dedicated to starting the engine at the PB
-2 6V batteries in series for bow windlass / bow thruster
-3 // batteries for edge services (instruments, fridge, lighting ...)
and 4 sources of energy:
-the engine alternator with its own regulator
-a dock charger at 3 outputs
-2 series solar panels controlled by a MPPT regulator
-1 wind turbine with its internal regulator

I want to replace the 3 service batteries with a big battery Lifepo4 200 or 300 AH that charges in DC / CV
it seems that I can adjust the regulators for that (except that of the engine alternator)
the problem is that I have no more regulation of lead batteries, and I do not want to change them all for lithium!
Or to charge a battery of 300 Ah discharged to 80% will take several hours to 14.4v
i have cyrix connectors to connect them during charging, but no load limiter (eg power off after 1 h charging at 14.4v)
charging currents can reach 40 A
is it essential to introduce a solar regulator for 40 A in front of each lead-acid battery?
please
Xavier
PS here is a diagram

Electric circuit.jpg
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izentrop
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Re: charge at the same time PB and Lifepo4 batteries




by izentrop » 08/11/18, 14:04

Hello,
xtaille@free.fr wrote:is it essential to introduce a solar regulator for 40 A in front of each lead-acid battery?
If 40 A is the maximum current generated by the PV, the battery must have a minimum capacity of 160 Ah and it will still be a cutoff system as soon as the voltage has reached the maximum voltage depending on the characteristics of the battery. http://www.ni-cd.net/accusphp/baba/plomb/charge.php

LifePo has more charge current, but has additional requirements for temperature monitoring and end-of-charge detection http://www.ni-cd.net/accusphp/baba/lithium/charge.php.
It is not justified on a boat that is not limited by the place and the weight?
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Christophe
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Re: Charge both lead and Lifepo4 batteries at the same time




by Christophe » 08/11/18, 14:22

Hi and welcome here

I'm also testing the mix of different technologies and it's not as easy as you might think.

The theory says that the lowest voltage battery and the highest capacitance will decide the paralleling voltage and the duration of the overall load: so if your Lifepo4 (much bigger) is not charged, your lead batteries will not be either. It will have a balance that will be created (= transfer of power from one battery to another). And this is not necessarily ideal for the life of the global installation ... it's case by case.

Ideally you should look at the charge / discharge curves of each battery to see "if it sticks" (more or less) and know how the BMS works (Internal charge / discharge regulator for lithium batteries for those who do not know what it means).

I was surprised to see that one of my BMS did not allow paralleling: it was only the other battery, with a higher discharge current capacity, which was discharging ... but, in my case, for the charge it's ok.

In short as I say the practice is not the theory! : Cheesy:

Your BMS indicates which charging voltage? Is it a common or separate port?

If you have a picture of the battery and especially the BMS it would help to see more clearly.

If not a solution already to implement quickly with your loader 3x45 A (diode internally I presume?):
a) load the 2 lead-in batteries AV and Engine with 1 phase 45 A, charging time at 80% = (50 + 75) * 0.8 / 45 = 2h15min about
b) load the lifepo4 with 2 phases of 45A, charging time at 80% = 300 * 0.8 / 90 = 2h40 ...

So you will reduce the difference ... at least when you load on the sector but I do not think that the batteries will discharge in the same way (in tension yes but not in capacity), that is why it is necessary see the voltage / capacity curves ...
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izentrop
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Re: Charge both lead and Lifepo4 batteries at the same time




by izentrop » 09/11/18, 01:03

Christophe wrote:It will have a balance that will be created (= transfer of power from one battery to another). And this is not necessarily ideal for the life of the global installation ... it's case by case.
It is clear that it is not interesting to put them in parallel, especially if they are reloaded at the dock.
It must be assumed that they are connected in turn is not it?
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xtaille@free.fr
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Re: Charge both lead and Lifepo4 batteries at the same time




by xtaille@free.fr » 19/11/18, 14:06

Christophe
I do not have the battery yet, so I can not say much about the BMS.
What the manufacturers say is that the LI .. charges at DC / CV (constant current / constant voltage) at about 14.4 V.
At this voltage, the PB batteries are also charged; but it is not necessary that it lasts too long, otherwise they s'esquintent.
And indeed, Izentrop, paralleling limited to the charging time.
So, for setting // I use Victron Cyrix switches, critters that I already use with satisfaction, and to limit the charging time it would limit the connection time depending on the voltage reached for a while which depends on the capacity of the monitored battery, basically a BMS adapted to a PB battery.
what comes closest to it is a solar panel regulator that is actually a current modulator depending on the relative voltage between input (PS) and battery output.
That's where I'm thinking.
Xavier
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