question

Jaco Reinecke avatar image
Jaco Reinecke asked

DC Ripple yet system is not running at full power as per Victron Wiring Unlimited manual.

Hi all,

I'm stumped.

Equipment:
Grid-tied, no feedback.
All on the latest firmware.
VenusGX
250/100 with 3.5kw array
MPII 5kva
BMV712
150ah Lithium bank with 50mm2 cables Less than 4m return.

The Victron Wiring Unlimited says, under DC Ripple, I quote: When measuring ripple, remember that this only occurs when the system is under full load. The same applies as for voltage drop. Ripple can only be detected when the inverter is powering a full load or when a charger is charging at a high current.


The scenario of today's 2 x DC Ripples warnings on the Venus:

On a SOC van 99-100%
AC Watts for the two DC Ripples:
Ripple 1) 1712w down to 562w
Ripple 2) 602w up to 1380w then down to 332w
Sunny clear day.

So I did a test with SOC 94%
Load powered 2000w.
Added another 2000w, inverter running at 4048w.
Removed the added 2000w load, inverter running at 2000w again.
SOC down to 93%
Never a DC Ripple.

Why is that, that under a small load, I get a DC Ripple, yet under max loads, no ripple?

A trick I pull that removes 99% of the Ripples:
Ripples tend to happen when I higher volts:
Bulk : 55.2v
Float : 54.4v

But if I set parameters to:
Bulk : 54.6v
Float : 53.4v
Nearly no Ripples, as I don't get to 100% SOC fast. :-)

Regards
Jaco Reinecke


Multiplus-IIMultiPlus Quattro Inverter Charger
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4 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Jaco Reinecke

99% sure your battery disconnects due to high cell voltage, what (kind of) BMS is in the battery?

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Jaco Reinecke avatar image
Jaco Reinecke answered ·

@Daniël Boekel (Victron Energy Staff)

I'm no expert with lithium banks nor BMS'es, but your answer mirrors my gut feel because it is not high loads causing the Ripples, but rather full batts with loads coming on, going off, the cause.

Would you agree I simply drop the volts to lower Bulk/Float, and carry on?


I have a Daly BMS, this one: https://lithiumbatteriessa.co.za/collections/frontpage/products/copy-of-bms-20a-8s-24v-lifepo4-lithium-ion-phosphate?variant=34759832273063

Temporary one till I find a BMS that interfaces with the Venus that does not cost a kidney, for DIY lithium banks ... or until we can find a developer to interface a BMS we found, that can give data, that is quite affordable to acquire.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Measure you cells to know for sure, probably one of them is higher than the rest.

you'll have to find the optimum charge voltage where the BMS will balance the battery, untill fully balanced, BMS will disconnect upon first cell reaching max voltage.

have a look at REC bms...

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Jaco Reinecke avatar image
Jaco Reinecke answered ·

Update ... the cells were out of balance, badly so, causing the DC Ripple.

On top of that, the BMS was not suited for running on a gird-tied solar system, it could never sort the imbalanced at 30mV balancing. On that point, even a 5amp balancer will struggle if ever get it right.

You have to have:
A grade Batch matched
That you have cells top balanced.
A BMS that gives you the voltage of each cell either on your phone and/or iPad.
And If the BMS can interface with the Venus using an RS485 port, then you are quite well positioned to avert a DC Ripple.

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marekp avatar image marekp commented ·
@Jaco Reinecke

18 cells ?

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Jaco Reinecke avatar image Jaco Reinecke marekp commented ·

Fixed my post to not confuse the matter as the reply was on the original problem I had, which was 16 x 150ah cells.

The 18 cell project is here: https://community.victronenergy.com/questions/111436/why-should-one-not-use-18-x-32v-280ah-cells-on-a-4.html

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David avatar image
David answered ·

150ah seems on the small side for a 5000va inverter?

.

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Jaco Reinecke avatar image Jaco Reinecke commented ·
150ah battery bank used off-grid maybe, but grid-tied used primarily to cover load shedding events, I reckon it is fine. Just be wise about it, as 150ah Lifepo4 cells can easily handle the max charge amps of 70a of a 5kva, if you want to do that.
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