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davidl avatar image
davidl asked

Help configuring generator for optimum use with a Multiplus II GX

Hello,

My system consists of the following:

4 x 320 watt solar panel

SmartShunt 500a

Bluetooth Battery Temperature

SmartSolar mppt 100/50

Multiplus II 24V 3000 GX

4 x 105ah Lead Acid Leisure Batteries

Kohler SDMO 6000A Diesel Generator

Its totally off grid there is no mains electricity.

Now its come to winter the solar is pretty much useless and as soon as I put a half decent load on the batteries the voltage plummets. The generator is set to come on using the assistants with the following settings:


Load Higher Than 1800w for 80 seconds & stop when load lower than 1000w for 60 seconds

DC input is lower than 23v for 10 seconds and stop when DC Input is higher than 28 for 60 seconds

Generator when started must stay on for at least 2400 seconds.


These are the settings I was told to use by the supplier of the multiplus II. So I accidentally left a water heater turned on and when its kicked in last night around 2000watts its dragged the batteries that low that the multiplus crashed and couldn't start the generator and everything went offline until solar kicked in this morning.

Tonight I had about 400watts of lighting switched on and the batteries read 24.4v as soon as i turned the kettle on (its a low voltage one) they dropped to 21v and when I turned it off again (straight away as i didn't want the generator to kick in) they went back up to over 24v.

I did this a few times to pull hard on the batteries then disconnected them and they read 12.5, 12.5, 12.4 & 12.3 (2 batteries are 2 months older there all the same make and model)

If anyone has any advice on what settings I should be using that would be great.


Multiplus-IIoffgridgenerator auto start
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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Davidl

If your batteries are subject to that winter cold, then indeed they'll show serious V sag under load. A Multi crash is a pain, and to avoid that at all costs, set it's trip point to the very minimum (18.6V?). By all means use alarms, as you need via VRM or however.

Not sure when you'd normally run that 'water heater', but if it's when the genset is running, then wire it to ACOut2. That way it can only start when the genset is on. ACOut2 can also be programmed with Assistants, so that doesn't preclude it's use at other times too.

Rather than using Vbat as one of the conditions to start/stop the genset, consider using SOC. I find it inefficient to run my genset above 95%, unless I have some decent loads on too. and I know 95% at the end of a solar day will get me through the night. I never look at Vbat, when winter cold makes it near useless to make decisions on when Pb batts need a genset boost.

The 40min minimum running time is also something you could take a closer look at. If batts are well up, and no big loads pending, then little point making it 'serve it's time'.


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davidl avatar image davidl commented ·
Hi John,


Thanks for the reply what is the trip point setting you mention?


The water heater I usually turn on first thing so I have hot water and then turn it off when I leave (my system runs a portacabin my acout1 goes direct to the main power input for the fuse board). I’ve changed the setting so that as soon as anything over 1500w comes on the generator will start within 15 seconds.


If I use SOC instead of Vbatt what %’s would you recommend I use?

As for generator runtime it was set to 30mins but I upped it to 40 mins but it could probably come down as after a while the charge wattage drops to like 200-300watts according to VRM.

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JohnC avatar image JohnC ♦ davidl commented ·

@Davidl

The 'trip point' is the 37.2V here (VEConfigure). 48V system shown. This is actually Victron default I think..

1672374691215.png

Really hard to suggest an SOC for you to work off. My 'emergency' level is 75% SOC, but I mightn't even run the genset if it's early morn and a good solar day predicted. But if I know poor sun coming, I may run it for a while when I know I can get max value from the genset. Usually organize it to run at the same time as any major loads planned for the day, like washers, etc. Hard to even program in all those preferences for an auto-start, so I don't.

And the lowest output I let my genset run down to is about 800W out of the 4800W I might get at full charge and loads. For your diesel genset I'd be somewhat worried about bore-glazing at low output. You may not be aware, and the maker/supplier might brush it off, but if you ever get that you'll wish you didn't have one.

With fuel costs as they are, look for any way to minimize genset runtime. Load er up for best results.

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