question

ehsab avatar image
ehsab asked

Small batterybank?

Hi,

I'm planning a 3-phase Quattro (5kVA 48V) setup and will use my system primarily as an UPS (until my genset kicks in).

I wonder what the minimum Ah is for such a scenario, would one string of 4x12V 190Ah suffice? Or is there something special to consider when designing the batterybank other then how long it will last?

I'm planning on adding solarpanels (or possibly a windmill) later on.

Anyone know if Enersys PowerSafe batteries are compatible or tested?
https://www.enersys.com/EMEA/PowerSafe_V_Front_Terminal_Batteries.aspx?langType=1033


Kind regards,

M

battery capacity
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5 Answers
kai avatar image
kai answered ·

Haven't checked your numbers - factors I would look at include:

* Genset delay (from grid loss to genset synchronised)

* Recommended discharge depth for the battery chemistry

* How often this happens (if not often maybe you can squeeze more from battery)

* Total weight, ease of replacement

* Nominal load or load profile during outage


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Kevin Windrem avatar image
Kevin Windrem answered ·

190 AH x4 implies about an 18 minute run time based on full load on the Quatro array (15,000 watts). That should be more than enough time to start a generator, and you could even wait a while before starting the generator. The down side in waiting is battery recharge time.

Check to make sure the current drawn from the batteries does not exceed their rating.

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JohnC avatar image
JohnC answered ·

Hi Ehsab. The real issue here will be how much power you have those Quattros delivering when your power fails. Too much V-sag could trip them before your genny winds up.

You could look to the batt maker's specs for a guide, and this can be pretty 'soggy' stuff. Let's say the spec is 0.1C recommended max discharge rate - so your 190Ah batts will be capable of 190 x 0.1 x 48 = 912W. A lot more than that might be too much. Time will be involved to some degree, and hopefully your genny isn't a laggard there..

You could wind your Quattro's trip points as low as they go, and let's say your genny takes 30sec to come onstream. A wild guess, but maybe you could make it with a load up to 3000W??

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ehsab avatar image ehsab commented ·

How are you calculating to reach a load of 3kW?

My goal is to be able to load 12kW from the batterybank, and i believe it will hold about 10-15min on that load.

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JohnC avatar image JohnC ♦ ehsab commented ·

Yeh, I did say 'wild guess', which I shouldn't do. My apologies, I owe you better than that, so I'll try again.

From this link (derived from your link):
https://www.enersys.com/WorkArea/DownloadAsset.aspx?id=25769807012chart

Using the 1.60 V/cell chart (which is awfully low but theoretically within your Quattro's limits), and without showing the math, you would appear to be quite correct at ~15 min rating.

They are actually rated down to 5 min (see Daniel's post), and they'd have no compatibility issues with Victron kit.

Lab conditions of course, and cold batts will have a hefty adverse effect. But those should actually work for you by the specs, if your genny doesn't take too long to warm.

My apologies again. You've done your homework, and I didn't do mine. I'd cringe at that sort of V-sag, but emergencies are what they are.. Good luck.


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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Eshab, for this purpose you want batteries made for UPS systems, as they are designed to handle high discharge loads, the batteries you linked to aren't.

UPS batteries will have 5 minute discharge rates, and up, while the powersafe batteries you linked to have the shortest rating at 30 minutes.

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ehsab avatar image
ehsab answered ·

Hi again,

So after some consideration i chose the PowerSafe SBS XC batteries instead.

Still two 48V strings of 190Ah (total 380Ah). According to the datasheet it should be able to handle 6000 DoD of 20% and 1500 DoD of 60%.

Anyone who sees any problems with this setup?


Range Summary
https://www.enersys.com/WorkArea/DownloadAsset.aspx?id=25769807928

Performance
https://www.enersys.com/WorkArea/DownloadAsset.aspx?id=25769807929

Operation Guide for Renewable Energy Applications
https://www.enersys.com/WorkArea/DownloadAsset.aspx?id=25769808085

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