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csf avatar image
csf asked

MPPT RS 450/100 charge voltage Flooded Lead Acid

I am hoping someone would be able to clarify the limitations on the maximum charge voltage of the RS 450.

I have a new batch of Rolls L16 Flooded lead batteries on a truck headed my way which is to be commissioned with a new 450/100. Upon looking at the manual produced by Rolls the charge voltage for my soon to be delivered batteries call for the following charge settings regular cycling:

bc32cbfa-1814-4c59-a0d9-482e4000b5d0.jpegI read the latest product update which states “Furthermore on the RS products, we found an issue in the derating of the output current by voltage, and when looking further into that decided to reduce the maximum programmable charge voltage. The highest configurable charge voltage is now 62V, and that will be changed to 60V. For most systems this will not be a problem, since they need charging at 57.6V or similar voltages below 60V. But for some it might and we apologise for the confusion around this.

The changes are:
1) Output current now derates from full rated current at 57V to 5A at 63V. Which will change to full current up to 60V and then derate linearly down to 5 amps at 62V.
2) The maximum configurable charge voltage will be reduced from 62V to 60V. Due to the internals, the MPPT RS really is not suited to work with batteries operating at those higher voltages.

In the coming weeks we will update the documentation to reflect above changes, as well as release firmware version v1.09, which implements them.”


I am hoping for clarification and or guidance with the setup of my new 450/100 related to this voltage limitation and the requirements of the battery manufacturer being higher.


Really hoping I didn’t purchase an expensive charge controller that can not charge or equalize a set of Rolls batteries?

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Alexandra avatar image Alexandra ♦ commented ·

@CSF

You have answered your own question.

Even at 62v the mppt cannot provide a high enough equalisation voltage. At 60v less so.

If you have a good relationship with your supplier you may be able to come to an agreement on an exchange.

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csf avatar image csf Alexandra ♦ commented ·

So in summary if I understand this correctly, if you are like me and purchased a 450 series mppt in 2021, which at the time had greater voltage capabilities for larger DC arrays, now being downgraded by firmware to something less capable, and with apparently less robust internals than say a 250/100. That particular charger as an example, that can handle a lead acid bank of Trojan (requires an even higher rate of 64.8 volts to equalize) or Rolls batteries in an off grid situation.

The answer can’t simply be to try and exchange it? That would imply an array that was wired for the 400+ volts would have to be redone, now requiring combiners, breakers/fuses and parallel strings with different wire gauges.

I will simply have to make this work with a combination of hopefully a generator and the Multiplus II and a manual charge, trusting that the 60v will still get me with temperature adjustment (hopefully) to a float at least, but I would love to see where exactly in the manual it stated in 2021 that the 450 is not suitable for off grid use using lead acid batteries the likes of Rolls or Trojan and that a 250/ would be better.

It is very disssapointing, a bit mind -boggling why this product was engineered in this manner that now leaves some of us in this situation.

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Alexandra avatar image Alexandra ♦ csf commented ·

Well, since I did not know the entire complexity of your whole situation, it was just a suggestion.


It was not expressly stated but even at the original 62v in the Tech Specs it was not enough for the install design you have in mind.

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2 Answers
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi @CSF , here the official answer:

After the issue was raised several weeks ago, we looked into it and the good news is that we are able to "relax" the derating compared to how it is in firmware now. But the bad news is that it still can't meet the specs as listed in the datasheet until recently.

The specs of the upcoming firmware update are:

----

The Charger set-point (absorption and float) can be set to max 60 V. The output voltage at the charger terminals can be higher, due to temperature compensation as well as compensation for voltage drop over the battery cables. The maximum output current is reduced on a linear basis from full current at 60 V to 5A at 62 V. The equalization voltage can be set to max 62V, the equalization current percentage can be set to max 6%.
----

I can understand how that is not meeting your requirement. And ofcourse you can get the product credited in full in case that is the situation.


This limitation, compared to our other products, is one of the side-effects of the technology in the RS, and not something we can easily address. So, for equalising batteries at such high voltages, another charger, or Multi will need to be used indeed. Or use another solar charger.

That is how it is, I can't make it any nicer I'm afraid. As also said in the other thread: this clearly didn't go as it should have - not good.

My apologies!


Matthijs

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csf avatar image csf commented ·
Thank you kindly for the explanation, and taking time from your busy schedule to answer my concern. Much appreciated.
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porcini avatar image
porcini answered ·

Hello,

normally there is no need for a 48V system or high PV voltages on a Truck.

Nevertheless almost every lead-acid battery can be charged with 2,35-2,45V/cell, depending on its usage. It also can be equalized using 2,50V/cell with a higher expenditure of time compared to the regular EQ voltage. Temperature compensation should hopefully work beyond these limitations.

However, if these batteries are for daily deep cycle usage this charger is not the way to go. You definitely need higher voltages then, especially when charging with time limited pv.

regards,

Porcini

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csf avatar image csf commented ·
Hopefully other folks looking at this system can learn from my situation with an off grid home running tried and true, and most importantly available for immediate purchase, lead acid banks at 48v (not truck) to perhaps look at other options seeing that this is still not clearly spelled out, but simply a footnote now in the fine print for these units.You need a different MPPT if you want your higher quality 2 or 6 volt banks maintained per manufacturer standards.
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porcini avatar image porcini csf commented ·

As already said there is no real need for voltages above 60V in good designed lead-acid offgrid systems since deep discharges only happen a few times a year. The Rolls' specifications are too high in my opinion and will shorten the battery life. Normally these are envisaged for traction use with daily deep cycles when it depends on time. I'm using lead acid batteries in off-grid systems for about two decades now and never charged them with more than 57,6V and -4mV/cell temperature compensation (60V for EQ). My previous battery lasted about 15 years. So if you want to keep the charger and you have a good system design with relatively flat cycles use the TABLE 2 (b) values and you'll be fine. For EQ use 60V with a longer duration when needed. If you have deep cycles daily then you have to use another charger with the Table 2 (a) values, but that's different from a real off-grid system then.

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