6kw battery back up

[maxomill]

I have a customer that has a 6kw 48 v battery back up . it has 2 sets of 4 100ah bats. the old bats are toast (3 yrs)and now im about to swop them for 2 sets of 4 Willard deep cycle bats. the old bats haven't hand much use in terms of load shedding and whatnot . which makes me wonder why the bats are finished.

5 of the 8 old bats (energiser maint free) all  are white  on the inspection glass and all fail a quick load test .

they are in  big garage so not getting too hot I don't think 

the charger is adjustable and I believed it to be correct but will check it with new bats

any one else got some suggestion's or  thoughts

I saw someone mention a balancing cable at the 24v point that had fuses  . anyone ?

 

thanks guys

cheers

 

 

 

 

[Chris Hobson]

1 hour ago, maxomill said:

I have a customer that has a 6kw 48 v battery back up . it has 2 sets of 4 100ah bats. the old bats are toast (3 yrs)and now im about to swop them for 2 sets of 4 Willard deep cycle bats. the old bats haven't hand much use in terms of load shedding and whatnot . which makes me wonder why the bats are finished.

Those Energiser batteries are not solar batteries. They're fine for the weekend camping trip but nothing more. Battery banks are like elephant herds (I can already hear Mark chortling "What the farmer on about now"). Large elephant herds are proportionately more destructive than smaller herds. If a herd is resting and a young restless bull snaps off a branch or breaks a small tree this will trigger other young bulls to follow suit showing their masculinity. So larger herds have more young elephants to provide the trigger.

Battery banks are the same. That is why a car battery tends to last as there are only 3 cells to fail - whereas a 48V bank has 24 cells any one of which has the potential to fail and there provide the trigger for the entire bank to fail. Energisers due their construction is like have a whole herd of young bull elephants.

1 hour ago, maxomill said:

I saw someone mention a balancing cable at the 24v point that had fuses  . anyone

I would recommend a HA02. These are excellent little devices. I know Chris-R and I are co-operating but I recommended them before our association and my partnership with him does not change how they perform. He has sold over 100 devices and has had not one return. 

[DeepBass9]

Hmm, analogy might be lost on the poor guy...

Not sure how you can get 6 k w out of 8 x 100, ah batteries, unless you discharge  them to 80%

[maxomill]

ta deepbass

15 hours ago, DeepBass9 said:

Not sure how you can get 6 k w out of 8 x 100, ah batteries, unless you discharge  them to 80%

but they are for a ups scenario  so if  the power goes down the load will never be 6 kw maybe 1.5 kw  . since someone seems to have the load shedding under control they rest alot

 

[___]

On 9/2/2017 at 9:36 AM, maxomill said:

I saw someone mention a balancing cable at the 24v point that had fuses  . anyone ?

That's a simple thin(ish) cable connecting the midpoints so that a single BMV can monitor both strings. In order to make it safe, a fuse is placed in this line. This is so that a failure in one string (which will immediately draw current over from half of the other string) does not burn that linking cable. It's only job is to transfer maybe a couple hundred milliamps during normal operation. Ideally you shouldn't link the midpoints at all, so this is a compromise, a "weak midpoint link" so to speak :-)

[___]

On 9/2/2017 at 9:36 AM, maxomill said:

the old bats are toast (3 yrs)

Sealed VRLA batteries for UPSes usually have a design life of 5 years, which means that if you keep them on float without ever discharging them, they'll be gone after 5 years anyway. Truth be told, I don't think these Energizer things are even of the quality of a good UPS battery, so that it didn't last 5 years isn't that surprising.

[SilverNodashi]

6Kw 48V, is that a Devel or IR inverter? I have seen those 6KW inverters drawing 6.7KW, full steam, till the batteries were dead. They don't have as an intelligent SOC calculator as the solar inverters have, so chances are the client has abused the batteries - even unknowingly. You should rather get batteries for UPS usage. The current bank you propose is also a big small. Depending on their budget, a BlueNova Lithium battery would be much better. It can handle the punch and will last much longer than a normal "deep cycle", VLRA or GEL battery could.