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tex260z asked

Victron 15/75 BlueSmart charger won't start

So the question has been asked before about charging LiFepo4 batteries with a Victron 15/75 e.g. BlueSmart charger, we all know about the +5V deal, the problem is everybody started blathering on about solar panel voltages, and then locked the comments, and the wasn't the question!

The real issue is Victron say to "Fully charge your batteries at least once a month", fair enough.

The question is how the hell do you do that with a charger if the van is in the shed in storage and there is no solar! The 5V difference means the battery would have to be below LVDC.

I have a changeover switch to go from solar to charger in my system, but it appears to be useless as the charger never kicks in. Am I right or am I right? It seems to me these chargers need a short duration "Trigger" voltage for charging Lithium batteries.

BTW everything works bonza on solar.

LiFePO4 & BMS connections + (with 3 way switch).pdf

charger
lifepo4-bms-connections-with-3-way-switch.pdf (1.6 MiB)
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jetlag avatar image
jetlag answered ·

I checked the values roughly and would recommend you to change the following:

JK-B2A8S20P BMS Start balance (V) - from 3,00V to at least 3,40 or even to 3,45V

Cell balancing unter 3,45V makes no sense, it will "destroy" the initial top-balancing.

The cells will always drift a little bit apart from each other, especially when there is load, and the active abalancer will try to compansate this, and through this it will unbalance the system.

So the balancer should be only active beyond the flat area of the charging curve. You can watch this up in a lot of youtube videos e.g. from Offgrid Australia. ;-)


One more point regarding "JK-B2A8S20P BMS Cell UVPR (V)":

I would not discharge that deep, the last few Ah below ~2,9V are ony 1-2% of the whole battery capacity. I know, this is only the disconnect voltage, but anyway try to not discharge that far down.

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jetlag avatar image
jetlag answered ·

Did you really connect the AC Charger (BlueSmart) to the PV Input of the MPPT Charger? This can't work out. Just connect it to the Battery (could be directly at the MPPTs battery terminals) and then this should work.

And in addition, this "load your batteries once a month" is not valid vor LiFePo4 batteries. This was fine for LeadAcid or AGM batteries, but LiFePo4 you don't need to keep fully loaded anyway. They will no degrade in low state of charge.

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ejrossouw avatar image ejrossouw commented ·

The once a month is intended to balance LifePO4 cells as it may otherwise not happen if the battery remains at say 60% SOC for extended periods. It is good practice and a battery manufacturer may even have such conditions for a warranty to remain valid. Other LA type typically requires a full charge per charging cycle.

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tex260z avatar image
tex260z answered ·

Yes Victron DO make that recommendation for lithium batteries (see their videos).

No, the switch switches out the regulator and switches in the charger and vice versa, (it even has an OFF in the centre).

Charger does (and should) go through the BMS and shunt, I would have though going straight to the battery and therefore back feeding the BMS would not be a good idea!

Batteries are balanced within 1 millivolt pretty much all the time.

At the end of the day the 5 volt question was still not answered??

My real issue is currently since fitting the new JK BMS it says the battery is at 61% and the BMV-712 says 100% even though I have set the SOC at reset as "Clear" because I can't get a proper cycle on the charger (or any charge with the battery currently sitting at 13.1V).

Guess I will just have to wait for a sunny day (not likely in Melbourne now) and drag the van out for a proper charge, annoying.two-way-switch-5.jpgtwo-way-switch-7.jpg


two-way-switch-5.jpg (1.4 MiB)
two-way-switch-7.jpg (940.9 KiB)
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tex260z avatar image
tex260z answered ·

Forgot I had this old HP power supply I sometimes use as a charger (works well), plugged that in and away she went charging perfectly.

The original question/assessment re. BlueSmart charger still stands, as I see it waste of money if you have lithium batteries?

hp-power-supply-1.jpghp-power-supply-4.jpg


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jetlag avatar image
jetlag answered ·

The BlueSmart Charger does deliver directly the battery voltage, so you should not connect it to the MPPTs PV input as it never will provide a high enough voltage to start the MPPT charging your battery. And yes, it should be conneted in a way, that all protective devices, like the BMS, are involved. I never said something different. ;-)

The +5V is a voltage-adder, a (Victron) MPPT charger needs to have more from the PV panel then the battery needs (e.g. 14V Battery -> 19V from PV, at least at the very beginning). This is to operate the MPPT intself and to allow some voltage drop during conversion.


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tex260z avatar image
tex260z answered ·

Do I really have explain it again? The charger does NOT go through the MPPT! I have a 3 way bypass switch! It goes directly to the battery via the BMS

So in the last couple of hours charging with 18 volt charger the battery is now nearly fully charged and the JK gauge and the BMV now both read the same state of charge, hoooray.

I think this proves my point that a BlueSmart charger (without any solar), is useless with lithium batteries, regardless of its "Lithium" setting

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Justin Cook avatar image Justin Cook ♦♦ commented ·

Part of the confusion is from the "BlueSmart Charger" being mixed in with the SmartSolar 75/15. They're two very different products, so the commingling of the titles is confusing everyone. The SmartSolar 75/15 of course requires vBatt +5V to charge, so yes if the van is without solar that won't work.

A BlueSmart charger is powered by AC, so it doesn't matter where you have a van parked, just plug in the charger. It will charge the battery, as it has nothing whatsoever to do with your solar.

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jetlag avatar image
jetlag answered ·

Your BlueSmart Charger might be defective.

I have the same charger (BlueSmart IP65 15A) and this works very good with my 180Ah LiFePo4 battery.

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tex260z avatar image
tex260z answered ·

No, it works fine connected directly to any lithium (or other chemistry) battery, I guess because everything! goes through the shunt, which is in turn connected to the BMV-712, that is where the limiting is being applied.

My issue is if I connect directly to the battery, what is that going to do to my brand new JK-BMS? I doubt that back feeding it would be a good idea, and there is no easy way to isolate it.

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jetlag avatar image
jetlag answered ·

I checked your diagram again, and the BMS should be connected directly to the battery and then the SamrtShunt should be connected.

And I don't know what you mean with "backfeeding", - putting current back through the BMS is just like charging... I have the same JK BMS for my 4S LiFePo4 battery and it is working great. I also load my battery through the BMS with the SmartCharger or with Solar when mounted in the caravan.

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tex260z avatar image tex260z commented ·

I was saying if I connect the charger directly to the battery terminals I am bypassing the BMS correct?

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jetlag avatar image jetlag tex260z commented ·
Yes, as I just answered further down in this thread, I see the BMS as part of the battery. So if I say directyl to the battery, the BMS is included in my mind. Otherwise I would say "directly to the cells". ;-)
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tex260z avatar image
tex260z answered ·

Ok, here we go again!
The old question arises, shunt before or after the BMS??
I went for before, for the simple reason that in the case of a LVDC from the BMS the shunt and BMV712 won't shut down and lose all it's data.
I realise it draws a tiny current but that doesn't concern me really, I have a google calendar routine to check the van voltage once a month, and I have never seen the cells very low even using the induction cooker, so I think I am good to go.
I can always set the LVDC a little higher anyways.

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jetlag avatar image jetlag commented ·

Yes, that is a valid point, but the BMS should be seen as part of the battery. It should have the shortest cables/connections to measure the best possible voltages (including all voltage drops caused by high currents) to be sure what is really happening with the cells. It is the "last line of defense". ;-)

This is a safety feature and should have more priority then some convenience features.

The terminals of the battery, where you connect all you loads and devices, is the point after the BMS like you would do with one of this commercially build batteries.

At least this is my opinion. ;-)

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tex260z avatar image tex260z jetlag commented ·

Don't think you could get them much shorter than that!

jk-bms-upgrade-17.jpg

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jetlag avatar image jetlag tex260z commented ·

Looks good, but nevertheless, the voltage drop across the shunt tells the BMS a different voltage at the cells as it realy is. And with e.g. 100A current and a lower SoC, the BMS might disconnect the battery because of low voltage then... Just my opinion. ;)

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tex260z avatar image tex260z tex260z commented ·

Victron spec says at 500 A current 50 mV (= 0.05 V) voltage drop over the shunt.

The JK can only do 200 A, so 20mV = 0.02 V correct?

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jetlag avatar image jetlag tex260z commented ·

Yes, should be correct.This should not cause major problems. ;-)

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tex260z avatar image
tex260z answered ·

Ok, another couple of months spent changing/checking/updating settings in all three devices.

Balance is now kicking in CHECK.

BMV is not reporting battery 100% at something like 12.8 volts, CHECK.

Under and Over voltages correctly set in JK-BMS, CHECK.

It appears at the moment this is the best this system has been in over five years.

Would anybody like to run their eye over my current settings for possible ultra fine tuning?

BMS & battery value variations.pdf

Oh and while I'm here just a heads up regarding the previous shunt before or after the BMS discussion. There is an ability in the JK-BMS control App to turn off charge and discharge, turning off discharge has two consequences, firstly your BMV-712 will lose all it's stored data, and second and more importantly, apparently with the current firmware if you then turn the JK-BMS back on it does NOT revert to the former battery type, but instead reverts to the initial battery setting in the unit when it is first booted, be WARNED!


bms-battery-value-variations.pdf (59.5 KiB)
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tex260z avatar image
tex260z answered ·

Thanks,

I have set Start balance to 3.45V.

I have set UVP to 2.75 (11V) and UVPR to 2.86 (11.44V).

As you can see cell manufacturer says 2.5V (10 V), so I think an extra volt should be good.

Incidentally Andy from TOGG says all the tests he has done over the years indicate there is nothing to be gained in using lower figures for LV and HV than are recommended by the manufacturer, he says use it all. Go figure?

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tex260z answered ·

Whoops! No I haven't for some reasons I cannot fathom I cannot set any of the UVP/UPVR/SOC 0% settings any higher than shown in revised sheet, some other setting seems to be blocking it. Tried variations of all three settings, no cigar.

Balance set to 3.45V fine. (trigger is set to 0.010V).

BMS & battery value variations.pdf


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jetlag avatar image
jetlag answered ·

Don't know why exactly you can't change the values now, sometimes it is a combination of other values...

But anyway, the setting is fine for a BMS. The main function is to protect the cells. And this is still given within the cell manufacturers voltage range.

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