Getting multiplus to float

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scraggs asked Feb 10, '23

Getting multiplus to float

Hi
I have my off grid setup working quite well now but I am having a problem getting the multiplus 2 to come out of absorption and go in to float, I can get the MPPT to go to float, I have a feeling this may be something to do with the tail current size which is not adjustable on the multi and the size of my battery pack, the only thing I can think of to get over the problem is to drop the absorption time further on the Multi.
Anyone have any better ideas ?
Setup is 48v 930ah (C5) traction battery
Victron 48/8000/110
Fronius 8.2-1
250/100MPPT ve can
Smartshunt 500
Cerbo GX
Thanks for any help

float

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kevgermany ♦♦ commented · Feb 10, 2023 at 09:41 PM

What tail current have you set on the multi?

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scraggs kevgermany ♦♦ commented · Feb 11, 2023 at 07:58 AM

Hi @kevgermany

The tail current can't be set on a Multiplus 2, I am sure I read somewhere that the Multiplus 2 tail current is fixed at 2 amps, I have it set at 18amps on the MPPT, which is 2% of the C5 rating.

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kevgermany ♦♦ scraggs commented · Feb 12, 2023 at 09:42 AM

Me being thick, sorry. The Multiplus only uses voltage, as JohnC pointed out.

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Answer 1 · 2023-02-11T04:26:49Z

JohnC answered · Feb 11, 2023 at 04:26 AM

Hi @Scraggs

I'm not a fan of the Adaptive algorithm in the Multi. It usually works out an Absorption time which is far in excess of what is sensible (at least for me). And even the Fixed time is only adjustable in full hours. A Tail setting like in the mppts would be a great improvement.

So you're really stuck with just a coarse Fixed setting, if the Adaptive isn't adequate.

Whether this is actually important to you as an offgridder depends on how you operate. I use a genset and rarely run it above 95% SOC, and never in Float. Just ain't worth the fuel for a Float current trickle. Maybe you're using the Fronius to finish off, so then understandable (sorta).

Maybe there's a way to use Assistants to terminate Absorb charge completely (no Float), using a Tail setting. For me that's like 99% SOC anyway at the same Tail I use in the mppt. Just thoughts.

This article is obviously old, but been redated 9/12/2019. See the end of Section 1. 20x times the Bulk period. Wow, not for me.. https://www.victronenergy.com/upload/documents/Adaptive_charging_how_it_works.pdf

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scraggs commented · Feb 11, 2023 at 07:52 AM

Hi @JohnC

Thanks for the reply.
It would be good if the Multi's had the same settings as the MPPT's, not being able to adjust equalisation voltage, amps and time is also a pain
I have looked at using an assistant to shut the charger off but can't really work out a way to do it, the only way I can see is to just give it an absorption time of one or two hours and let the MPPT take care of things if it needs longer.
The problem I am having is because the tail current can't be set the multi is always staying in float for the set max time time when the battery is actually where is should be charge wise and is making it gas unnecessarily.

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