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"Blue" power trolley


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Hi "Blue team",

Here's my plan for a power trolley, as backup power for work-from-home:

- Victron MultiPlus 12/800/35-16

- 2x Omnipower 180Ah AMG/Gel battery bank

- 6A, 1-Pole, 6kA Input & Output Breakers

- 25A On-Off-On 1-Pole Change Over Switch

- 25mm2 Cables to battery bank

-  2.5mm2 20A AC leads from Eskom and to the load

(I plan to mount the inverter to the cabinet's lid )

 

IMG_20200813_143206.jpg

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1 hour ago, GreenMan said:

I have often pondered the following:-

As 220V is potentially lethal would an earth leakage not be advisable ? The ELCB would not be required if all devices connected to the backup power are double insulated but what if they are not ?

 

Thanks, I'm considering organising a qualified sparky to hook this all up, to be on the safe side

 

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Connected up the "power trolley" yesterday, in time for a 2-hr load-shed last night. Ran our 55" LED, a lamp and 2 routers fine.

I'm not finding many local source for a DC circuit breaker for the batteries. I've had suggestions from the 80A fuse in the diagram, to a 40A AC/DC breaker at a local electronics shop.

How do I identify which rating is best?

E.g 80A DC circuit breaker

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5 hours ago, [email protected] said:

I'm not finding many local source for a DC circuit breaker for the batteries.

It's usually best to use a DC rated fuse on the DC side; it can be a type that disconnects (so it can act like an isolator). Fuses will usually be able to interrupt the short circuit current of the battery; often circuit breakers cannot.

The one you link to above has 10 000 written on it, possibly meaning that it can interrupt up to 10 kA. That's probably just enough, unless you expand your battery to over 200 Ah (assuming LFP).

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1 hour ago, Coulomb said:

It's usually best to use a DC rated fuse on the DC side; it can be a type that disconnects (so it can act like an isolator). Fuses will usually be able to interrupt the short circuit current of the battery; often circuit breakers cannot.

The one you link to above has 10 000 written on it, possibly meaning that it can interrupt up to 10 kA. That's probably just enough, unless you expand your battery to over 200 Ah (assuming LFP).

I have 2x 180Ah (nominal rating is 150Ah) in parallel, so that puts me over the 200Ah mark? These are GEL, not LFP though.

I'll just order a proper 80A fuse to be safer.

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Those batteries can give 2x 180A/hour, but that does not mean they will. You are limited by the usage from the battery (i.e. the inverter). 

The fuse/breaker is there to safeguard the cable. The inverter will normally use 800W @ 12V. That is 66.7A. (P = I*V, so I = P/V)
It can peak over that for a short while, so 100A will be fine
And 100A will be fine for your 25mm2 cables as well at 130A max. Although 35mm2 is better for 125A, your inverter will not use that much.

So look for 100A-125A fuse/breakers. Some good value ones can be found here (I cannot comment on the quality, but the other items on Brian's store has had good feedback)

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20 hours ago, [email protected] said:

I have 2x 180Ah (nominal rating is 150Ah) in parallel, so that puts me over the 200Ah mark? These are GEL, not LFP though.

Duh, somehow I didn't see the first post with the photo.

Gels are about 20C short circuit current (thanks to my colleague Weber in this post), so that's 180 x 2 x 20 = 7200 A or 7.2 kA. But you also mention AGM; they're 40C, so that would be 14.4 kA. It depends on whether they really are AGM, or whether it's another abuse of the term for marketing purposes. Assuming that the battery modules will be paralleled (your diagram shows 12 V). I note that if they were put in series (so you had a 24 V inverter), then the current would be halved.

I wonder though it you'd be saved by the fact that arcs don't tend to sustain until the voltage reaches about 24 V. 

20 hours ago, [email protected] said:

I'll just order a proper 80A fuse to be safer.

Safe is good.

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  • 2 weeks later...

To date it's kept our laptops and routers running like a charm for 3 load-shedding slots.

I've hooked up a MK3-USB interface and noticed that after 2 of those, the inverter had switched to "Storage" mode, which I'd only expect if there's been no load with full batteries, within the past 24hrs.

The first was after a 2-hr session at night. The next morning I saw that the inverter was in Storage mode. I shut it down and after restarting, it ran the absorption charge setting and then switched to float, as expected.

The next one was after a 4-hr load-shed, it switched to Storage mode although the battery was on 89% SoC. A restart again resolved this. I'm going to speak to the supplier about this. Some googling indicated this could happen if the voltage had not dropped sufficiently to trigger the correct sequence. I'm a bit nervous that this could cause the batteries not to be fully recharged during consecutive load-shedding events, without intervention.

Next up I've connected a Raspberry Pi loaded with the Venus software image, so that it's easier to see what's ticking.

 

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On 2020/09/06 at 5:52 PM, [email protected] said:

I've hooked up a MK3-USB interface and noticed that after 2 of those, the inverter had switched to "Storage" mode, which I'd only expect if there's been no load with full batteries, within the past 24hrs.

The first was after a 2-hr session at night. The next morning I saw that the inverter was in Storage mode. I shut it down and after restarting, it ran the absorption charge setting and then switched to float, as expected.

The next one was after a 4-hr load-shed, it switched to Storage mode although the battery was on 89% SoC. A restart again resolved this. I'm going to speak to the supplier about this. Some googling indicated this could happen if the voltage had not dropped sufficiently to trigger the correct sequence. 

Info as I have it about the multi's "decision" about initiating a bulk charge is as follow:

This is for a 12V system. (Multiply by 2 for 24V and by 4 for 48V.)

For lead batteries, the system switches back to bulk when the voltage drops 1.3V, or more, below the configured float voltage.

For lithium batteries, the system switches back to bulk when the voltage drops 0.2V, or more, below the configured float voltage.

 

So most likely due to the fairly light load (about 100W?) on a basically new big (for your described load) battery, the battery voltage did not drop low enough (as you suspected). This will probaly also be more likely if the load shedding instances were fairly close on the heels of having just completed absorption stage where the battery voltage was still quite a bit higher than the float value.

On 2020/09/06 at 5:52 PM, [email protected] said:

 the voltage had not dropped sufficiently to trigger the correct sequence. I'm a bit nervous that this could cause the batteries not to be fully recharged during consecutive load-shedding events, without intervention.

ESS has an option "to keep" batteries charged" but I have no idea whether you can add the ESS assistant wihtout adding PV to the system ( @plonkster ??) .... If you are truly concerned about needing the batteries fully charged between sessions a low tech option could be to just up the load a bit to the point where you know a 2 (4 hour?) hours load shed will trigger a bulk/absorb charge.. or reduce the battery bank capacity (take out a battery).... but take a close look at how often you are likely to have frequent consecutive load sheds with a risk that more than one will push you beyond your selected Depth of Discharge or have no useful time for a recharge (if 4 hours used just over 10% you have quite a bit left in the tank for another session or two... then if needed you can still manually "reset").

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1 hour ago, introverter said:

ESS has an option "to keep" batteries charged"

No GX device in this system.

Storage mode activates if you've been at float more than 24 hours (if I recall). It's a non-gassing voltage (it extends battery life) but it doesn't completely counter-act self-discharge, so a periodic recharge cycle is done.

To get out of storage mode, however, the voltage needs to drop low enough, and I'm not quite sure what is low enough, but if it doesn't the charger does not go back to bulk.

Simplest solution: Use VE.Configure and disable Storage mode. Storage mode is no good for regular power failures. Only use storage mode if the batteries really spend long periods at float, by which I mean more than a week at a time...

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4 minutes ago, introverter said:

seems like a venus paai (OCD meter probably struggeling with that one 😉)  has been added in the mean time.. post 11 in the thread: "Next up I've connected a Raspberry Pi loaded with the Venus software image, so that it's easier to see what's ticking."

Aaah ok. I scrolled right to the top, didn't see one, and made assumptions 🙂

Yes, you can run ESS on a backup inverter... you still need to disable storage mode though. Otherwise the inverter will still drop the charge voltage after 24 hours... and will then Keep the batteries "charged" at this lower voltage. In other words, it would not really be any different to what you have now.

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