battery drains unnecessarily on no load

Thread Starter

falade47

Joined Jan 24, 2017
153
i just changed new set of batteries after suspecting the batteries might be responsible for the inverter system not lasting as usual..but the same thing still happens ,it still drains down like before..could there be a problem with the inverter system?..
 

Thread Starter

falade47

Joined Jan 24, 2017
153
The problem is that you have provided no information to work with.

Les.
The problem is I don't know what other information to provide..if you'll please ask me..haven't opened the inverter yet..it just drops so rapidly on no load, just like a countdown..i need help before the client #kills me..
 

AnalogKid

Joined Aug 1, 2013
8,489
Your post #1 reduces to this: I have something that doesn't work well. Tell me why?

"before" what?
What is "usual"?
"inverter system" means at least three *very* different things. Which one is yours?
What batteries? Manufacturer, part number, capacity, photos - anything?
Does your inverter use a car battery to make 10,000 volts to charge an electric fence?
Photos of the unit.
Input voltage/current/power?
Output voltage/current/power?
Intended use?
a.n.y.t.h.i.n.g...

ak
 
Last edited:

Thread Starter

falade47

Joined Jan 24, 2017
153
Y
Your post #1 reduces to this: I have something that doesn't work well. Tell me why?

"before" what?
What is "usual"?
"inverter system" means at least three *very* different things. Which one is yours?
What batteries? Manufacturer, part number, capacity, photos - anything?
Does your inverter use a car battery to make 10,000 volts to charge an electric fence?
Photos of the unit.
Input voltage/current/power?
Output voltage/current/power?
Intended use?

ak
Yeah thanks for coming in..the system is a 48v 7.5kva inverter unit which initially takes up 60% load up to 3hrs. But currently even on no load I have on the lcd screen the battery capacity and percentage which goes down in no time(makes me sick)..the batteries are AGM batteries 12v 200AH each connected in series in line with a 7.5kva cyberpower inverter.i suspected one of the batteries to be at fault cause I tried a battery tester and found out one the batteries dropped so low to 9v while the rest maintained 10-11v..so I decided to change all batteries but same thing still happens..maybe battery again..
 

dendad

Joined Feb 20, 2016
3,566
How old are the batteries?
Those voltages sound like the batteries may be at the end of their life.
It is critical the you never let them get that low in voltage. Doing so will greatly decrease their life.
The min each battery should be allowed to go is 11.6V
Never let them sit in a discharged state. That will kill them.
Does your inverter have a low voltage cutoff to help protect the batteries or do you just run it until it stops?
 

LesJones

Joined Jan 8, 2017
2,667
What is the specified input current for the inverter with no load on the output ?
What is the MEASURED input current for the inverter with no load on the output ? (At the moment with the suspect fault.)
What is the voltage AT THE INPUT TERMINALS OF THE INVERTER when the display on the inverter shows that the batteries are low ?
0.6 x 7.5KW = 4.5 KW from the 48 volt supply this is 4500/48 = 93.75 amps. I do not think the battery capacity will be near to 200 Ah at such a high discharge current. The battery manufacturer probably supplies graphs of the capacity against discharge current. You need to look at them to get proper information. NOTE both mine and Alec's calculations are base on 100% efficiency. The inverter will probably only be about 90% efficient so the situation will be slightly worse than these calculations predict.
Another thing to consider is how good the design of your charging system is. It could also be that a fault has developed on the charger and the batteries are not being fully charged.

Les.
 

Dodgydave

Joined Jun 22, 2012
9,206
Y

Yeah thanks for coming in..the system is a 48v 7.5kva inverter unit which initially takes up 60% load up to 3hrs. But currently even on no load I have on the lcd screen the battery capacity and percentage which goes down in no time(makes me sick)..the batteries are AGM batteries 12v 200AH each connected in series in line with a 7.5kva cyberpower inverter.i suspected one of the batteries to be at fault cause I tried a battery tester and found out one the batteries dropped so low to 9v while the rest maintained 10-11v..so I decided to change all batteries but same thing still happens..maybe battery again..
Get yourself a Dvm and measure the current drain with no load, and also measure the battery voltage every 30mins.
 

strantor

Joined Oct 3, 2010
5,291
That requires 7.5 kW x 0.6 x 3h = 13.5 kWh of energy (assuming unity power factor).
Battery stores only 48V x 200 Ah = 9.6 kWh of energy.
Doesn't look like a good match.
plus the Peukert effect.
Assuming the battery brand matches the inverter brand, here are the batteries:
https://technowave.co.za/backup-battery/25837-cyberpower-cps-rbp200-vrla-12v-200ah-agm-rechargeable-battery.html
Nominal Capacity
20 Hour Rate (10.0A, 10.5V) 200Ah
10 Hour Rate (19.0A, 10.5V) 190Ah
5 Hour Rate (34.0A, 10.5V) 170Ah
1 Hour Rate (120.0A, 9.6V) 120Ah
following this:
0.6 x 7.5KW = 4.5 KW from the 48 volt supply this is 4500/48 = 93.75 amps. I do not think the battery capacity will be near to 200 Ah at such a high discharge current.
It appears that the 94A load puts the batteries somewhere between the 1hr and 5hr rate. So I'm going to estimate 140AH is the true capacity at this discharge rate.
94A/140AH = 1.5 hours runtime.

I think
the system is a 48v 7.5kva inverter unit which initially takes up 60% load up to 3hrs.
..i need help before the client #kills me..
I think either the client is lying to you about how long it used to run, or you've replaced the batteries with inferior batteries.

Curiously, this is the highest capacity CyberPower inverter (7200W) I was able to find around the stated power (7500W). It's stated runtime at half-load (close enough to 60%) is 13 minutes. Has the inverter in question been modified to have a higher capacity than from the factory? If so, I would suggest it be modified better.
 

JoeJester

Joined Apr 26, 2005
4,264
I would do an equalizing charge and test the batteries individually. 100 AH at the 20 hour rate is like a constant 5 amperes for the whole 20 hours.

You can build a disconnect circuit that would disconnect the load when the battery reaches the low cell limit, and stop a counter that would display the elapsed time.
 

Thread Starter

falade47

Joined Jan 24, 2017
153
What is the specified input current for the inverter with no load on the output ?
What is the MEASURED input current for the inverter with no load on the output ? (At the moment with the suspect fault.)
What is the voltage AT THE INPUT TERMINALS OF THE INVERTER when the display on the inverter shows that the batteries are low ?
0.6 x 7.5KW = 4.5 KW from the 48 volt supply this is 4500/48 = 93.75 amps. I do not think the battery capacity will be near to 200 Ah at such a high discharge current. The battery manufacturer probably supplies graphs of the capacity against discharge current. You need to look at them to get proper information. NOTE both mine and Alec's calculations are base on 100% efficiency. The inverter will probably only be about 90% efficient so the situation will be slightly worse than these calculations predict.
Another thing to consider is how good the design of your charging system is. It could also be that a fault has developed on the charger and the batteries are not being fully charged.

Les.
Thought so as well..might just be the system unit sending a wrong info(don't know how that is done) to the charging system that the batteries are fully charged perhaps the battery are still pretty low, I discovered the battery percentage moved up to 100 all the way from 60 within 10mins..-to me that is bad-..its probably not a high charging current, maybe a system malfunction..
 
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