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mahargrenrut avatar image
mahargrenrut asked

Parallel Multiplus Charging low

I have added a second multiplus 24v 70a 230v device in parallel to an existing multiplus.

I was expecting to see at least 100+ amps of charging when in parallel.

1 / Both devices are the same

2 / Both devices have the latest firmware

3 / Both devices are set up in to run in a Master and Slave configuration

4 / They are charging two Victron Lithium batteries (2 x 200AH 24v)

5 / The system delivers the correct passthrough current (now 32 amps)

6 / Inversion works at full capacity 5K+

7 / All settings are set to max charging 70a each (140a total)

8 / The original single multiplus delivered 60amps continuous charging from 50% to 99% seamlessly

9 / Tests have been run when all devices are cool

The two together will not deliver more than 77 amps in parallel. While I don't expect it to deliver 140amps I would have expected at least 100+. Lithium technology is capable of accepting more current than this. I added the second unit to help increase charging capacity as well as inversion capability

Can anyone shed any light on why this is happening.

Thanks in advance

Lithium Batterymultiplus in parallel
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7 Answers
mahargrenrut avatar image
mahargrenrut answered ·

CLOSED - I have now fixed the problem

Turning off Weak AC has now increased charging from 73 amps to 120 amps.


3.1 Derating of the power factor

Some generators have a waveform which makes it difficult to charge with the normal charge mechanism. Through activating the “Weak AC input” function, another mechanism is used which will enable the MultiPlus to charge under practically any condition.

Disadvantage of using this option is that the input power factor, normally equal or close to 1, will be degraded. This function should be used only when the preceding ones are ineffective.

This leading or lagging power factor will have the effect of demanding more kVa from the generator for the same or less DC Watts delivered to the batteries. You may need to further reduce the DC Current Limit in the Charger tab of VEConfigure if the generator continues to overload after changing this setting.

Effectively, when Weak AC is enabled, the total charge current possible will be less that the rated maximum charge current output of the charger (under normal conditions).

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Alexandra avatar image
Alexandra answered ·

@Mahargrenrut

Since the victron batteries have their own BMS control, they are the ones telling the system what to do here.

What size cable do you have on the system? How is it wired? It is also possible that the cabke resistance has come into play as well.

What inverters exactly do you have installed?

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mahargrenrut avatar image mahargrenrut commented ·
Hi Alexandra, thanks for the reply. My cable length is quite long (5m) from Multiplus to Batteries. I have 70mm cable (1.5m x4) exactly the same length from batteries (under seat to Lynx distributor. From there they run through 95mm cable to engine room where they meet fused cable 1.8m (all exactly the same length 70mm cable to two parallel multius units. They are identical Multius 24v/3000/70 units. Each unit will deliver 65/70 amps to batteries on there own but when in parallel they won't go above 79 amps. An extra 9 amps from an additional inverter does not seem right to me even taking into account resistance etc. If one can deliver 90% why can't two?
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mahargrenrut avatar image mahargrenrut commented ·

My 55 amp (24v) alternator manages to deliver 47 amps to the batteries (as measured on the smart shunt next to the Lynx distributor. When I run the multis with the alternator the current goes up to 120amps. Again if a simple alternator (with Balmar controller) can deliver 47amps why can't a second multius do the same?

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mahargrenrut avatar image mahargrenrut commented ·

Two multiplus together max 73 ampsscreenshot-20220430-165101.jpg

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screenshot-20220430-165101.jpg (253.0 KiB)
mahargrenrut avatar image mahargrenrut commented ·

Two Mtius with 55amp alternator running 120amps

screenshot-20220430-165054.jpg


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screenshot-20220430-165054.jpg (256.8 KiB)
Alexandra avatar image
Alexandra answered ·

@Mahargrenrut

Input current limit?


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mahargrenrut avatar image
mahargrenrut answered ·

The imput current is controlled by the digital panel and set to 32amps. It was limited to 16amps when I had only one unit. Even when I am charging at 74amps I can still pass through 2kw so I don't belive that is the issue. It doesn't matter if I have no loads or lots of loads it won't go past 74amps

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mahargrenrut avatar image
mahargrenrut answered ·

I have also put a meter on the DC outputs of each unit. They read 37/38 amps each. This shows that they are balanced but not running at full capacity.

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mahargrenrut avatar image
mahargrenrut answered ·

I would be grateful if an engineer from Victron could please shed some light on this issue.

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Philip avatar image
Philip answered ·

Hi,

I have excatly the same issue, two parallel Multi 12V 1600VA 70A on one phase L1. Inverting of the system works great at 3200VA but charging is limited to 70A (LifePo4 with DiyBMS). Did you find a solution ?


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