A heads up about some server rack batteries.

[FilterGuy]

I am seeing posts of people wanting to build 48V systems with 5 or 6KW inverters and server rack batteries. This is a nice, clean way to build a system, but be aware of the current limits on a lot of the server rack batteries.

I just saw this for the Pylontec batteries:



A 5000W inverter at 90% efficiency can draw as much as 116A, so a proper system would need 5 of the US2000C batteries.

The LiFePOWER4 is a lot better:


But you would still need 2 of them to properly provision a 5K inverter.

I have seen other batteries with surprisingly low current limits. My main point is: Be aware of the battery limits and make sure the battery bank meets the needs of the inverter.

 

[schmism]

I am seeing posts of people wanting to build 48V systems with 5 or 6KW inverters and server rack batteries.

5-6kw inverters.... seems like 280ah or so is a sweet spot for battery size. so for your examples, the 3000c to hit that kind of capacity you need 4 in parallel which then has an output in the 150a range which is reasonable for a 5-6kw 48v inverter

 

[FilterGuy]

5-6kw inverters.... seems like 280ah or so is a sweet spot for battery size. so for your examples, the 3000c to hit that kind of capacity you need 4 in parallel which then has an output in the 150a range which is reasonable for a 5-6kw 48v inverter

Yes, the 3000C has a recommended 37A, therefor 4 of them in parallel should be OK. However, the 2000C is another story. The 2000c spec 'recommends' 25A and says it will shut off after 60seconds of 50A. What the spec does not tell us is what happens if you run the battery at a continuous 30A or 40A.

I am hesitant to run something beyond the recommendation so I would probably not set a system up that could draw more than 25 amp from a 2000C for any significant amount of time. When you run the numbers, that means 5 batteries would be needed. If you are willing to run the batteries at 30A for an extended time, 4 batteries would work.

Either way, the spec for all of the Pylontec batteries have a crazy low recommended discharge current.

 

[robby]

I am seeing posts of people wanting to build 48V systems with 5 or 6KW inverters and server rack batteries. This is a nice, clean way to build a system, but be aware of the current limits on a lot of the server rack batteries.

I just saw this for the Pylontec batteries:

View attachment 89930

A 5000W inverter at 90% efficiency can draw as much as 116A, so a proper system would need 5 of the US2000C batteries.

The LiFePOWER4 is a lot better:
View attachment 89931

But you would still need 2 of them to properly provision a 5K inverter.

I have seen other batteries with surprisingly low current limits. My main point is: Be aware of the battery limits and make sure the battery bank meets the needs of the inverter.

Are you sure about this?
Reading the Lifepower4 manual it states 30A Recommended. (See below)


Then it goes on to state that those 100A constant numbers are actually for 10 & 20 Seconds.

Now normally I would give this a pass but we know the Lifepower4 has had problems starting Inverters that other batteries including the Eg4LL have started!

So on one hand you have the largest Pylotech at 3.5Kwh stating 37A Recommended Max continuous Discharge and the Lifepower 5.1KW stating 30A Recommended Max continuous Discharge. The surge on the Pylontech says 90A for 15 seconds and the Lifepower is 100A for 10 Seconds (Kind of a wash and actually better for the Pylontech considering it's a much smaller Battery pack)

Maybe I am missing something?

 

[FilterGuy]

Maybe I am missing something?

No.... It looks like I missed something.

Your additional clarification just reinforces my main point: The discharge rate for these server rack batteries is crazy low.

 

[timselectric]

No.... It looks like I missed something.

Your additional clarification just reinforces my main point: The discharge rate for these server rack batteries is crazy low.

Part of the reason for this is probably because these cases are unvented. Heat has a harder time dissipating. This is one of the reasons why I have decided to vertically mount mine. Rather than stacked, in a cabinet.

 

[mnd]

Wow, those are very low BMS settings.
Or cheap BMS's
Thanks for the heads up.

I've got a DLG which has similar (low) limits; they're using physically smaller cells so the current limit seems to be limited by the cell rather than the BMS (which doesn't seem to be cheap.)

The Amphenol RADSOK connectors also have a 120A rating, so you don't want to be drawing more than that from a parallel string.

 

[houseofancients]

No.... It looks like I missed something.

Your additional clarification just reinforces my main point: The discharge rate for these server rack batteries is crazy low.

it really depends on what bms is used.
the seplos bms does 100a for the 100a rated one

 

[robby]

it really depends on what bms is used.
the seplos bms does 100a for the 100a rated one

View attachment 90039

I would dig deeper. Just like the LifePowers first Spec sheet says 100A Constant and then goes onto clarify 30A recommended. Then they later clarify that the 100A is only for 10 Seconds. When Seplos says MAX 100A i suspect that has a small time limit on it and is not a sustained drain.

eFlex batteries which cost more than double the price uses a huge Relay instead of Mosfets and it can deliver 60A continuous and 100A for 60 minutes.

 

[robby]

No.... It looks like I missed something.

Your additional clarification just reinforces my main point: The discharge rate for these server rack batteries is crazy low.

I would add in the words "Budget Server Rack". The expensive ones can do double the Amperage or even 1C constant discharge rate for pretty long periods.

 

[jberger]

The lower continuous amperage models appear to really be made to be used as backup power for telco applications, like cell towers.
When I was shopping, the low C discharge rate was a clear difference in the models offered, so I'm guessing that they are built for a backup market, not really for ESS.

 

[Solar Guy Richard]

I would dig deeper. Just like the LifePowers first Spec sheet says 100A Constant and then goes onto clarify 30A recommended. Then they later clarify that the 100A is only for 10 Seconds. When Seplos says MAX 100A i suspect that has a small time limit on it and is not a sustained drain.

eFlex batteries which cost more than double the price uses a huge Relay instead of Mosfets and it can deliver 60A continuous and 100A for 60 minutes.

Just to clarify, it's GREATER THAN 100a is considered over-current and that's the 10s mark. Up to 100a does not engage over current protection.

 

[FilterGuy]

Just to clarify, it's GREATER THAN 100a is considered over-current and that's the 10s mark. Up to 100a does not engage over current protection.

OK..... Why is the recommended current so low? What happens if the system continuously operates higher than the recommended current but below 100A?

In other words: How do we use the recommended current for designing the system?

 

[robby]

Just to clarify, it's GREATER THAN 100a is considered over-current and that's the 10s mark. Up to 100a does not engage over current protection.

Same Question, so your saying run it at 95A all day and I will have no problems?
I am noticing the exaggeration in product statements and documentation by Signature Solar to be very consistent and that is really disturbing.

 

[houseofancients]

I would dig deeper. Just like the LifePowers first Spec sheet says 100A Constant and then goes onto clarify 30A recommended. Then they later clarify that the 100A is only for 10 Seconds. When Seplos says MAX 100A i suspect that has a small time limit on it and is not a sustained drain.

eFlex batteries which cost more than double the price uses a huge Relay instead of Mosfets and it can deliver 60A continuous and 100A for 60 minutes.

i am running their 200 bms ( with my own build cell pack, and it will happily do 200a continues.)
if you look at the resource section, i posted the manual for the 100a rs485 version of this bms.

please take a look at chapter 4

100a continues charge
100a continues discharge

 

[Solar Guy Richard]

Same Question, so your saying run it at 95A all day and I will have no problems?
I always find the lack of accurate documentation by Signature Solar to be consistent and disturbing.

It is rated, per the manual, at 100a constant output. I will contact the manufacturer and find out why there is a 'recommended' limit of 30a and let you know.

 

[Steve_S]

Ping to @Will Prowse as I think this is a thread he may want to chime in on and maybe offer some enlightenment as he has a fleet of server rack packs.

I have looked at Telecom Battery Packs (Rack mount) and several are indeed lower amperage but not all. I have suggested to people especially in the EU to look for "Telecom Battery", as they are more available there from what I've seen and always tell them to Check the Specs Carefully, which really applies to everything these days.

EditS: From the various reviews I've seen that Will has done, they have all had proper BMS' capable of handling full on ESS use.

 

[GXMnow]

Just something to keep in mind here, solar storage is rarely ever going to be even close to 1.0C rate.

I have now been running my house essentially off grid for a few weeks. My system charges when the sun shines, and discharges all night. I do have a 6,800 watt inverter, but my average power to or from the batteries is more like 1,500 watts. I have peaks that will hit 4,000 watts, but they don't last very long. The big test will be running air conditioning, but even then, It is 15 minutes on, and 15 minutes off of 3,200 watts. We need the storage to last for at least 5 hours to be worth while, so that means an average of 0.2C rate or less.

Last night, my house only used 11 KWH from battery over 12 hours. Let's just round that off to 1,000 watts. And I have 36 kilowatt hours of battery. We got very good sun again today, so the battery charged that power back in 6 hours of sun. So we can call it 2,000 watts average charge power, it hit a peak of almost 3,000 watts, but again, not for long. My charge and discharge rates are never exceeding 0.1 C rate. If I maxed out my XW inverter, it is still under 0.2C on charge or discharge.

If your system is cycling the batteries faster than that, it won't make it through a day, probably not even the 5 hour peak rate window. If I was using these server rack batteries, I would use at least 5 of them in parallel, and it would take 7 to match my battery bank. With 5 of them, that 30 amp current limit becomes 150 amps, more than the 140 amp limit of the XW inverter/charger. 30 amps on a 100 amp hour battery is 0.3C. SO you would only get a little over 3 hours at that rate. If you have enough battery for a useable energy storage system, you won't need over 0.2C charge or discharge rates in real life. The only place this might become an issue is if you have a pump or some other load that needs a lot of power but for a short time. In those cases, you do need to ensure your battery system is up for it. 1C for a few minutes should be good, but make sure.

 

[Steve_S]

Just something to keep in mind here, solar storage is rarely ever going to be even close to 1.0C rate.

Thank You for pointing that out.

 

[hammertoe1]

If your system is cycling the batteries faster than that, it won't make it through a day, probably not even the 5 hour peak rate window. If I was using these server rack batteries, I would use at least 5 of them in parallel, and it would take 7 to match my battery bank. With 5 of them, that 30 amp current limit becomes 150 amps, more than the 140 amp limit of the XW inverter/charger. 30 amps on a 100 amp hour battery is 0.3C. SO you would only get a little over 3 hours at that rate. If you have enough battery for a useable energy storage system, you won't need over 0.2C charge or discharge rates in real life. The only place this might become an issue is if you have a pump or some other load that needs a lot of power but for a short time. In those cases, you do need to ensure your battery system is up for it. 1C for a few minutes should be good, but make sure.

I guess one usecase that might go against this, is if you are wanting purely a battery backup system. ie. you want to use grid power/solar for the majority of the time, and just want a battery for backup in case of a grid outage. So maybe you want the battery to just give you an hour of power, say. So you might have a fairly small battery (Single digit kWh) paired with a larger inverter and might be expecting to discharge at a higher rate.