Good day all

I have a newly installed system Axpert 5Kva 

SOL-I-AX-5P

8 x 200Ah 12volt sealed gel deep cycle batteries connected in two banks 48v each, series parrallel , so 48v with 400Ah battery. Currently totally reliant on the grid, no Solar connected yet.

If my average load is 1500 watts and I want to only drain batteries by 40%, how long will I be able on my batteries as per above. Is there a formula to work this out?

1st question, got it set to charge up to 58.5 volts and to float at 55 volts. When there is a power outage or I simulate one, the voltage drops down to about 52 volts within minutes, even on a 800watt load. It seems to then drop very slowly. If I switch on the aircon, as an example, it uses about 1000watts when running, this drops the voltage at a slightly faster rate, then if I switch the aircon off battery voltage improves again. Is that normal?

Also I set it to 48volts to shut down batteries, is that voltage ok to shut it off or is it to low or to high.

2nd question, the fans run consistently, although quietly when batteries charged and on float.  Is that normal? Obviously when the system is running on battery fans run faster and slightly nosier then on recharge the fans make quite a racket. Got the battery AC charger set on 40 A .

3rd question, where to get the latest power watch software - any links please, 

Lastly for now, if I relocate the inverter to get less noise, its currently in my living room, how far away from the battery banks can it be located. I have nowhere else to move my batteries, could put inverter in next room but that means the pos and neg to the inverter, those 16mm cables, will be 4 to 5 metres between inverter DC connectors and first connection to batteries. Any advice please. 

 

Another quick one, I have circuit breakers on each bank of batteries, could I isolate the batteries once fully charged and then just switch then on every week for a few hours. I am told these deep cycle batteries can hold a charge for 3 months - is that true?

 

Info, advice on any of these questions will be much appreciated. 

Thanks all

Mike

 

Edited May 25, 20197 yr by Mike Nofal
Mistake

2 hours ago, Mike Nofal said:

If my average load is 1500 watts and I want to only drain batteries by 40%, how long will I be able on my batteries as per above. Is there a formula to work this out?

Sure. You have a nominally 400 Ah battery, usually we use a battery voltage of 50 V to make the numbers round. So that's 20,000 Wh of energy, or 20 kWh. To only drain by 40% (40% DOD, down to 60% SOC), you are only using 40% of that, or 40/100 x 20,000 = 8,000 Wh. Ignoring losses, at an average load of 1500 W, your battery will last about 8,000 Wh / 1500 W = 5.33 hours. Now take off 10% for inverter and battery losses, that makes it 5.33 x 0.9 = 4.8 hours.

So the formula for other loads would be t = 7200 / p  where t is the time in hours, and p is the load in watts.

2 hours ago, Mike Nofal said:

1st question, got it set to charge up to 58.5 volts and to float at 55 volts. When there is a power outage or I simulate one, the voltage drops down to about 52 volts within minutes, even on a 800watt load.

That's 54 / 4 = 13.0 V per nominally 12 V module. That's totally normal. You have to "push" power into the battery to lift the voltage beyond 13 V per 12 V module.

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It seems to then drop very slowly. If I switch on the aircon, as an example, it uses about 1000watts when running, this drops the voltage at a slightly faster rate, then if I switch the aircon off battery voltage improves again. Is that normal?

 

Yes, totally normal. It's also normal for the battery voltage to sag a little with higher loads. Though 1000 W is C/20 for your battery (a twentieth of its amp-hour capacity), so that's pretty light, and the sag would be minimal.

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Also I set it to 48volts to shut down batteries, is that voltage ok to shut it off or is it to low or to high.

It depends on many factors. It's probably fine, and I suspect you can't set it higher.

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2nd question, the fans run consistently, although quietly when batteries charged and on float.  Is that normal?

Yes.

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3rd question, where to get the latest power watch software - any links please, 

https://www.mppsolar.com/manual/Watchpower (off-grid)/

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Lastly for now, if I relocate the inverter to get less noise, its currently in my living room, how far away from the battery banks can it be located.

It's one of those "shorter is always better" things. The longer the cable, the thicker it needs to be to minimise losses.

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I have nowhere else to move my batteries, could put inverter in next room but that means the pos and neg to the inverter, those 16mm cables, will be 4 to 5 metres between inverter DC connectors and first connection to batteries.

Cables are usually measured in cross sectional area of copper (ignoring insulation), i.e. in mm² (millimetres squared, sometimes written as mm^2). It happens that 16 mm² is a standard metric cable size, but it's way too thin for a 5 kW inverter. Perhaps you are measuring the cable diameter, including insulation; double insulated 50 mm² is just under 15 mm diameter. You should be using at least 35 mm², unless you are limiting the inverter power to perhaps 4 kW. I certainly would not be extending the battery cable to over 4 metres with 16 mm² cable.

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Another quick one, I have circuit breakers on each bank of batteries, could I isolate the batteries once fully charged and then just switch then on every week for a few hours.

I would not be disconnecting the batteries routinely, unless you have a pre-charge system. Connecting the batteries causes a massive (1000 A or more) surge of current to charge the capacitors in the inverter. This is very hard on the circuit breaker contacts. You can use the rocker switch under the inverter to turn them mostly off. But be aware that they still draw significant power (around 35 W, from memory). I would turn them on to top up the battery once a week.

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I am told these deep cycle batteries can hold a charge for 3 months - is that true?

It depends on many factors; when new, perhaps. But only about 3 weeks with the 35 W drain.

Thank you Coulomb,

Appreciate you taking the time to give me these answers.  Very helpful indeed.

Regards, Mike