Axpert Low Voltage Warning Error

[Bush Man]

Morning to All!

I have the 5KVA 48V Axpert connected to 2x4 150Ah Omnipower Batteries.  

The Axpert's low voltage cutout is set at the highest possible setting - 48V..

 It's very rare for me to go below 50V. On the odd occasion in the past that I did so, the HS04 Low Voltage Warning started blinking at around 49V, and the system cut out at 48V.

Of late, the low voltage warning starts blinking at around 51V, and the system cuts out at around 50V.  This is despite the low voltage cutout setting still being at the highest possible 48V.

Any ideas how to set this right?

 

[Guest]

My first inclination will be to check the batteries for a potential problem.

Why I say this is that volts may look right but the minute the battery gets under any kind of load, the volts drop very fast.

And that always points to a faulty cell / battery in my experiences.

[pilotfish]

To expand on what TTT has already said...

It sounds like you have one or more failed batteries in the bank causing voltage of the bank to fluctuate under load. If this is the case then continuing to operate under those conditions will cause failure of more and eventually (quickly!) all of your batteries.

• Disconnect grid feed and solar feed so that only the battery bank is supplying the load,
• wait for some time to allow surface charge to dissipate (or for your low battery alert if you have the time),
• then disconnect all loads so that the battery bank bank is idle,
• then measure the voltage of each battery individually, they should be virtually identical.

If you identify a battery failure you will need to consider your options,

• if the other batteries in the string containing the failed battery are still fresh and showing similar voltage then you may be able to replace just the failed battery
  • this is contrary to common advice but replacing 8x OPS150 will cost a bit, 
• if the bank is getting on or showing a wide voltage variation then you may need to visit your bank manager.

After carrying out the remedial action that you decide on you must implement some method of centre point voltage monitoring (look for BMV-702 on the forum) which will identify this fault at an early stage - it wont save the failed battery but may save the others. Also look up HA-02 battery balancer which may help to prevent similar failures in future.

 

 

 

 

[Gerald_db]

For a 5kva inverter is a 300Ah bank maybe a bit small and been pushed a bit hard hence a cell failure?

Sent from my SM-G920F using Tapatalk

[Arandoza]

As far as I recall the 5kva axpert recommends a
Minimum of 200ah battery pack, for a single inverter, 400ah for 2 in parallel etc.

200ah is not that much considering one probably can use only 25 ah - to
Keep the dod low and then also to allow any loses, and inverter consumption as well.

[Chris Hobson]

35 minutes ago, Gerald_db said:

For a 5kva inverter is a 300Ah bank maybe a bit small and been pushed a bit hard hence a cell failure?

Sent from my SM-G920F using Tapatalk
 

Just depends on loads. I have a 200Ah battery bank but the loads it needs to carry overnight are low. Nevertheless the small loads still results in a DOD of 30-40%. 

2 minutes ago, Arandoza said:

As far as I recall the 5kva axpert recommends a
Minimum of 200ah battery pack, for a single inverter, 400ah for 2 in parallel etc.

200ah is not that much considering one probably can use only 25 ah - to
Keep the dod low and then also to allow any loses, and inverter consumption as well.
 

25 Ah is DOD of only 10%. One probably would want 10% to get reasonable life out of standby batteries. If one has proper deep cycle batteries a DOD 10% is perhaps not economically sound as one is not really using one's batteries.

[Guest]

2 hours ago, pilotfish said:

• Disconnect grid feed and solar feed so that only the battery bank is supplying the load,
• wait for some time to allow surface charge to dissipate (or for your low battery alert if you have the time),
• then disconnect all loads so that the battery bank bank is idle,
• then measure the voltage of each battery individually, they should be virtually identical.

The above is right, but to properly test a battery, it needs a load on it, done per battery, using a load tester, on fully charged batteries.

On UPS'es, I used volts before to test, always showed 12v+. Only time I got instant answers was if they are like 10v, or 3v or 0v on a 12v battery.

Then I bough a small 12v little vacuum cleaner and let it run on the smaller batteries. Results are near instant on a problem battery that measured like 12v.

On the bigger batteries, one has to use a load tester like the ones they use to test car batteries. They put them under severe strain, you can smell it, to make sure the volts stay where they are for those few seconds. Results are again instantaneous.

And FWIW, never in all my attempts have I ever been able to resurrect a battery. Maybe I do things wrong, even though I bought a few devices over the years that claimed they can resuscitate batteries. After even weeks on them, never a success.  Sorry.

 

A suggestion: Because we all have devices that need batteries, nothing stops us from going small banks to just connect them. Problem is, the smaller the bank, the lower the amps the less the panels are used in the day.

So AN idea is to use 2nd hand batts with near no drain on them at night just to get the daily power usage. 

IF power failures return, then get a proper bank again, for there are no sums yet that can make batteries cheaper than Eskom at night - unless you are off-grid or have to use a generator. 

[Bush Man]

Thanks to all!

I'm in a remote off grid location, so that makes load testing a bit complicated.

The system was commissioned in September last year. About two months ago I checked and noticed that on the one bank there was a substantial voltage variation. The lowest was at 11V and the highest above 13V (no irregular low voltage warnings at that point).  The second bank was well balanced. At Chris Hobson's advice I brought the lot back to town.  I charged all the batteries to around 13V, and they all held their charge perfectly for the three weeks that I monitored them. The only exception was the 11V one, which wouldn't accept charge at all. Sinetech tested and exchanged it for me.

I re-installed the lot with a HA-02 battery balancer on each bank.  My typical load is very small - energy efficient fridge (600Wh per 24h) and LED lighting (say 300Wh per 24h) only.  6x250W panels in 2 strings of 3.

It's a big schlep to bring the lot back to town for testing.  Is there no reliable test that can be done with my voltmeter? There is a 1500W microwave oven which I use occasionally for a minute or two, so I can put a load on the system for testing purposes.  

My voltmeter readings have always agreed with the Axpert reading to within 0.1V.  If there were a bad cell, would the Axpert not show an actual low voltage reading? Why would the low voltage warning start blinking at 51V if it is only supposed to do so at 49V?

My sense is that I should start by resetting and reprogramming the Axpert in case it became confused somewhere along the line?

[Guest]

28 minutes ago, Bush Man said:

It's a big schlep to bring the lot back to town for testing.

Good point. Ask around town for someone who can lend you a Hawkins load tester. Or rent it if they don't want to just give it.

Voltmeter readings will not work and because they are such big batteries, a small load can take hours/days to show a result.

[pilotfish]

If you cant find the Hawkins load tester then try the following;

Borrow a 3kw oil heater (or similar load), plug it into the inverter and disconnect all other loads so that you have a constant current drain on the batteries, then measure the voltage of each individual battery under constant load - if you have a failed battery i am pretty sure it will reveal itself.

If results are difficult to interpret try the same test with only 1 battery string connected at a time (but test both strings because you may have more than one failed battery), I would suggest disconnecting both HA-02 prior to this test because they will probably confuse the result.

[Guest]

1 minute ago, pilotfish said:

... a 3kw oil heater (or similar load) ...

Will work.

Reason why I did not suggest similar is that in the end one always have to home in on the individual battery/ies that are problematic.

Unless you have a 12v inverter and a big load ... 

[Chris Hobson]

1 hour ago, Bush Man said:

My voltmeter readings have always agreed with the Axpert reading to within 0.1V.  If there were a bad cell, would the Axpert not show an actual low voltage reading? Why would the low voltage warning start blinking at 51V if it is only supposed to do so at 49V?

The problem is Axpert  voltage is over the whole bank and to identify a failing cell you need to look at individual batteries. You may have a situation where the cell holds charge but as soon as it is under load it fails and so you have a rapid drop in voltage the inverter shuts down and the voltage immediately recovers.

I think your 48V cutoff is too high. I assume that you are having the inverter shut down early morning. If a load momentarily causes you voltage to drop below 48V you have a shut-down.

[Bush Man]

Morning Guys!

Spring and overcast weather is with us again.  

In my off grid situation, when the Axpert shuts off due to low voltage, will it restart by itself when the batteries have charged again, ot do I have to reset it by switching it off and on again using the power switch at the bottom?

[___]

22 minutes ago, Bush Man said:

will it restart by itself

Having read many threads about this inverter's configuration, I believe it does have a setting for when it is supposed to restart after a low voltage shutdown... so it would be very odd to have such a setting and then not use it :-) I conclude therefore that yes, it will restart by itself, unless someone comes along and tells me it cannot do this.

I do know newer models dropped the small AC power supply that earlier models had, which would allow it to wake up if another AC source (grid connection, generator) came online, so at least on that end it is possible that it won't restart by itself.

[Bush Man]

Thanks, Plonkster

It's an 5kVA Axpert in a remote location and I have guests out there. Wouldn't like them to start fiddling with switches unless necessary.  Will give it until lunchtime. Fridge should be OK until then.

Low voltage cutout is set at 47V, but after a sunless day yesterday they had two hair dryers going this morning, with predictable results.  Sounds as if it is sunny today though.

[Bush Man]

For the record, it did come on by itself after a couple of hours of sun.

[Coulomb]

On 2018/09/08 at 9:08 PM, Bush Man said:

For the record, it did come on by itself after a couple of hours of sun.

Yes, the SCC has its own way to turn on the inverter, independent of the usual inverter on/off rocker switch.

[ Edit: I assume that firing up a generator will not wake a newer model from low voltage shutdown, however. I never let my battery get that low that it cuts off due to under-voltage, so I can't speak from experience. ]

[ Edit 2: However, it seems my assumption is wrong. ]

Edited October 21, 2018 by Coulomb