question

eliott avatar image
eliott asked

Significant parasitic current with Multis

Hi!

I have noticed that in a charger only setting there are significant parasitic currents consumed by Multis, especially larger ones. In the standard system design schema, however, there is nothing between the Multi and the Smart Lithium battery to shut off this connection in case of low voltage, the system relies on the BMS to turn off the inverter, but still the parasitic current remains.

In these systems the cell voltage of the batteries can go well below 1 volt.

What is the suggested solution to this problem? I was thinking of adding an extra Cyrix-li-load between the battery and the Multi but those would be too small for the inverter currents. Any suggestions? We are talking about legacy systems, so using the new smart BMS is not an option.


thanks

Eliott

Multiplus-II
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2 Answers
Trevor Bird avatar image
Trevor Bird answered ·

Hello @eliott , if you are leaving the multi for a long period and have no other way of charging the batteries, perhaps shut down the Multi when the battery SOC reaches a certain level. A CerboGX could be programmed to energise a relay at a predetermined SOC. That relay could be wired to the remote control input to the Multi. That provides a protection mechanism that is separate from a BMS and saves any current drain when the batteries reach a level that is set by you. You could set it so that say, at 60% SOC the multi switches off. The batteries can then simply remain at 60% SOC until the system is visited.

Regards

Trevor

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seb71 avatar image
seb71 answered ·

Disconnect the inverter from the battery if the system will not be in use for a long time.

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eliott avatar image eliott commented ·
Obviously. And what is the foolproof solution? What is the poin of having a BMS when it does not protect in all scenarios
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seb71 avatar image seb71 eliott commented ·

If there is no other protection (and even if there is), the inverter should be set to shutdown at no less than 48V (about 3V cell voltage for a 16-cell LiFePO4 battery). From here to 1V cell voltage there is some time to act. Or the Sun rises and panels charge the battery back.

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