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dtg255 avatar image
dtg255 asked

Multiplus II-GX killed RS485 to USB adapter

Hello,

I tried to connect an EM24 RS485 to a Multiplus II GX using the original Victron RS485 to USB interface.

The EM24 is already installed and metering. I connected it with the interface cable to my laptop and had access to the EM24. Everything was fine.

Then I switched the interface cable from the laptop to the Multiplus. As I put the plug into the USB port all LEDs in the plug flashed an then it died.

At the moment the Multiplus is only powered via AC-IN. No batteries or anything else is attached.

Does anyone have an idea what I did wrong?

Thanks

Guenter

Multiplus-II
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5 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

Don't run the multiplus WITHOUT battery attached!!

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dtg255 answered ·

Thank you for your answer! I think this lesson had to be learned ;-)

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misterx1000 answered ·

Hi. I have a question about this topic.

Is it completely "impossible" to run the MP2 without either no battery, or no AC in connected?

Thank you very much for your help

Alex

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gazza avatar image gazza commented ·
I am also interested in this... I have run the Multiplus with "just" AC IN, for programming and testing of RS485 link to ET112 without any problems? So I was suprised to see that this may "kill" the RS485 to USB communication adapter? I can only imagine that this was caused by some sort of surge in voltage or current. If you put a multimeter , for example, across the battery terminals(with NO battery), and measure voltage what happens....? Well, basically if you plug the AC IN to mains 240v and switch the rocker switch to charger only then the voltage on the battery terminal starts to increase from zero very slowly to around 1.7v while the Multiplus boots up. Then the internal relay (that senses the grid voltage) kicks in and the battery terminal voltage increases rapidly towards charge voltage, but there is no battery which triggers the Low Battery Voltage alarm and the voltage drops back to just above 40V. I am thinking that during this transient change there is a possibility that the USB socket may also experience some transient voltage surge?
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crash-override answered ·
Hi, it is because of missing galvanic isolation of your RS485-USB adapter, most energy meters us a capacity-based power supply for its electronics, this power supplies are not isolated. Most energy meter vendors use a isolated RS485 interface. I recommend you a isolated RS485 adapter to avoid this issues. The Multiplus can run without batteries attached, but this is not recommended, the manual says this product is designed to run with a battery. I configured my too with open battery circuit breaker in charge-only mode, to avoid problems with a instable DC bus if it try to start inverting. My BMS blows the battery circuit breaker because of different cell balancing state and multiplus try to feed in with power from mppt directly, the DC bus fluctuate wildly and my Multiplus stopped feeding in properly without destroying anything. I hope this helps a bit. You can measure different voltage with a multimeter and rs485 lines to ground for example, if its tied to ground or neutral you see logic voltage levels 3-7V, if its isolated you have voltages aroung 50-60VAC.
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misterx1000 avatar image
misterx1000 answered ·

Thank you very much for your answers.

I think I understand it now. So it seems to make no difference if I use AC only or battery only to keep the MP2 alive because the RS485 adapter gets killed because of the missing ground isolation (to the EM24 energy meter).

I will try now to use an USB isolator. My plan is to connect this isolator directly to the MP2-GXs USB-port. There I want to connect an USB extender where I finally connect my USB/RS485-Adapter-->EM24.

Hopefully this will work and help :-) I´ve heard that the MP2 is a little bit "bitchy" which USB hardware it accepts. We will see...wish me luck :-)

Thank you again an best regards!

Alex

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