Hi Folks,
I'm thinking about trying to load-balance/share the battery banks of my multiple separate APC UPS.
The idea here is that the load against each UPS is not the same during an outage, and I'd like to maximize uptime for all my devices by pooling all of the batteries together, rather than having a separate battery bank per UPS.
In the DC power domain, this is relatively simple, just parallel each 120V DC battery bank, so you stay at 120V DC, but share the load across all batteries.
For example, if you have four UPSes, and each UPS has 10 x 12V batteries in series, you will now have say 4 sets of 10 x 12V in series, with each set in parallel, so 40 12V batteries in total, still maintaining 120V.
In this case, the DC chargers are also attached in parallel, which, since all the batteries and chargers are identical, shouldn't be an issue, either (though it could be if the chargers try to be too intelligent).
BUT, the catch is that there are a couple of APC proprietary "temperature/data" wires for each battery pack. I assume that if these aren't connected to satisfaction, the UPSes may do things like turn on the fans at inappropriate times. One idea I have is to run each set of temp sensors to a separate UPS (while paralleling everything else).
But, the UPSes do already support up-to 10 external battery banks each, so I sort of wonder if the "data" lines can already just be combined naively (or whether there's some extra complexity where the UPSes transmit the max(N) battery temperature, or something like that.
Really, I'm just wondering if anyone else has already done this before? It seems like a fairly obvious approach to improve load balancing and reliability if you have multiple separate UPS units, but everyone seems to opt for much more complex approaches where they either run UPSes in series or more rarely parallel on AC power, including synchronizing the sine wave outputs with one UPS being master and the others slaving to that. Much more complex stuff, and I'm not sure why people prefer to combine power in the AC domain instead of the DC domain (there are some benefits, but they don't seem worth the complexity to me).
For anyone who will say "just connect 4 battery banks to your single UPS like APC wants you to do" -- sure, now you have a single 3000VA UPS with 4x the runtime. Doesn't solve my problem. I want 12000VA net (4 x 3000VA, each a separate inverter, not a combined 12000VA like if I had combined the inverter AC outputs like many have done) AND sharing that combined runtime because they all draw from the same batteries - so they'll all "die" at the same time, not die at different times depending upon their relative current draw.
I'm thinking about trying to load-balance/share the battery banks of my multiple separate APC UPS.
The idea here is that the load against each UPS is not the same during an outage, and I'd like to maximize uptime for all my devices by pooling all of the batteries together, rather than having a separate battery bank per UPS.
In the DC power domain, this is relatively simple, just parallel each 120V DC battery bank, so you stay at 120V DC, but share the load across all batteries.
For example, if you have four UPSes, and each UPS has 10 x 12V batteries in series, you will now have say 4 sets of 10 x 12V in series, with each set in parallel, so 40 12V batteries in total, still maintaining 120V.
In this case, the DC chargers are also attached in parallel, which, since all the batteries and chargers are identical, shouldn't be an issue, either (though it could be if the chargers try to be too intelligent).
BUT, the catch is that there are a couple of APC proprietary "temperature/data" wires for each battery pack. I assume that if these aren't connected to satisfaction, the UPSes may do things like turn on the fans at inappropriate times. One idea I have is to run each set of temp sensors to a separate UPS (while paralleling everything else).
But, the UPSes do already support up-to 10 external battery banks each, so I sort of wonder if the "data" lines can already just be combined naively (or whether there's some extra complexity where the UPSes transmit the max(N) battery temperature, or something like that.
Really, I'm just wondering if anyone else has already done this before? It seems like a fairly obvious approach to improve load balancing and reliability if you have multiple separate UPS units, but everyone seems to opt for much more complex approaches where they either run UPSes in series or more rarely parallel on AC power, including synchronizing the sine wave outputs with one UPS being master and the others slaving to that. Much more complex stuff, and I'm not sure why people prefer to combine power in the AC domain instead of the DC domain (there are some benefits, but they don't seem worth the complexity to me).
For anyone who will say "just connect 4 battery banks to your single UPS like APC wants you to do" -- sure, now you have a single 3000VA UPS with 4x the runtime. Doesn't solve my problem. I want 12000VA net (4 x 3000VA, each a separate inverter, not a combined 12000VA like if I had combined the inverter AC outputs like many have done) AND sharing that combined runtime because they all draw from the same batteries - so they'll all "die" at the same time, not die at different times depending upon their relative current draw.