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houser avatar image
houser asked

Help with Multiplus that does not start when no PV is available.

Hello,

Edit: as I got information from Victron that DVCC does indeed help with startup peak surge
so that is no longer a question. It does help.

When attempting to start a Multiplus 48 5000 during certain conditions, there are low voltage warnings and DC ripple and shutdowns of both battery and Multiplus. I assume this is something people with LieFePo Canbus battery have seen?

One main part of the problem is of course that a CanBus LiFePo battery will allow various different DCL and CCL depending on conditions so will for example not allow the Multiplus to start during certain cold conditions, so some form of acceleration resistance or the like may be required regardless but may not help during certain conditions.

I also assume attempting to start the Multiplus when the current is not there is not very good for the Multiplus, nor the battery when the current from the battery is not there. Is it dangerous?

I have built a conditional switch for now in Node Red that will not allow startup during certain conditions. I am also assuming that the battery is doing some form of protection that I can not see over CANBus/DVCC,

Grateful for any comments. Many thanks.







Multiplus-II
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3 Answers
Elimac avatar image
Elimac answered ·

Very confusing...

Resistance on the PV side of the MPPT should only translate into losses. See resistivity formula on Google. What may be helping is the fact that you have another source of power besides the Battery. If PV is not connected, maybe the MPPT charger has output capacitors that also need charge, and the resitance of output cables (not input) may slow down the spike.

Maybe the BMS is capping the initial spike caused by charging the input capacitors of the Multiplus? The typical problem of initial charge?

If so, maybe use a small value /high power resistor with a switch to provide initial charge, prior to turning on the Multiplus. Maybe a good idea to install a small panel voltmeter on the DC input to watch the voltage rise.


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houser avatar image
houser answered ·

Thanks @Elimac !
Sorry if my question is confusing. I am watching the system closely and trying to figure out what is happening. I know for sure that having some small current at the solar panels takes away the issue. All the specs for the system are well within the recommendations and the peak capability of the battery is rated as 500A. But that capability is also changed based on conditions by the battery BMS.
I also found this about other (Redflow) batteries that require a similar tweak to handle the same Multiplus II 48 5000 that might be related or similar?

Your suggestions make sense. Many thanks.

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Elimac avatar image Elimac commented ·
Very interesting document. Can be useful in some cases to know that. But in your case I don't think it will help. In fact, could make it worse if indeed you are having the initial charge problem. You start from the point where Multiplus is turned off, right? If that's the case I would rule out for now DC ripple and focus on the (possible) initial charge issue or continue investigate for another explanation.
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houser avatar image houser Elimac commented ·

Thanks @Elimac ,

Yes, Multiplus turned off is starting point for this issue.
What is empirically reasonably clear so far from tests is that:

1.
The Multiplus will always start without issues if the PV yield is at leat around 200W or more.

2.
The Multiplus will have issues when there is no PV wattage coming in which is obviously the case when DCL is 0 via CANBus battery/DVCC. That is a bit of a Catch 22.
The only way to start the Multiplus under such conditions is to start the generator.
I have not forced those tests at all, just noticed when it happened as I assume it is not good for battery nor Multiplus, but it has happened enough times that the pattern is pretty clear.

Many thanks.

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klim8skeptic avatar image
klim8skeptic answered ·

What is the capacity of the battery?

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houser avatar image houser commented ·
It is 120A, rated for 120A continuous and 500 peak.
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