idiot-ranch
New Member
TL;DR:
Hi all, this is my first post to the forum, but it's already been incredibly helpful.
The existing system...
My wife and I recently purchased a ranch and with it a slightly older but really well designed off-grid solar setup that powers a couple small cabins, well pump, etc.
The system includes two strings of solar totaling 8kW theoretical, but offset directionally so that we get ~5kW max, but solid power throughout daylight hours in winter.
Most components are produced by Outback Power, which includes two Radian GS8048A's set up for split-phase output while also controlling a 9.2kW Stamford generator. Charge controllers are Outback's FLEXmax 80, and the system uses the other components from Radian like the communication hub, load centers, and Mate3.
I had never used their stuff before but have been very impressed! The only thing that is wrong with the system is a surprisingly under-sized and old bank of lead-acid batteries, which now faults when drawing over ~2kW.
New batteries...
Yesterday we ordered four 48V EG4 LiFePOWER's, which is the minimum needed to fully utilize the inverters. We don't yet have a good sense for daily energy needs, since many of the traditionally higher-power loads use propane (stove/oven, water heater, dryer) and we don't live there full-time. The major draws are the well pump and some mini-splits, but so far we've never used much more than ~4kW, and even then not continuously. We almost ordered 6 batteries to fill out the cabinet and provide longer runtime, but decided to play it conservative and potentially save $3k by starting with 4, with plans to add 2 more soon if we find we want them. We don't mind having the generator come on occasionally if needed, but really don't want it running continuously (especially under low [inefficient] load).
Question about fuses...
With the new battery bank, I want to make sure everything's protected from short-circuit loads. My inclination is to think of the cabinet as a self contained and protected system component, so I'd like to put the fuse or fuses inside the cabinet. This doesn't seem to be particularly common here, and I'm curious why? Is there something I'm not thinking of?
RE sizing fuse sizing, I'm working with the following stats from our 2 Radians, each of which list:
The BMS of the EG4 batteries has the following BMS behavior listed under "discharge":
Looking at the blow delay curves of the Blue Sea Class T fuses, it appears that I can safely size the fuses to the "continuous" values of our load without risking it tripping under normal peak/surge/instantaneous conditions. The real purpose is to protect the wiring/BMS from much larger short-circuit loads, though, and so it's presumably important that the fuse trips faster than the BMS. While I've found resources like this, I'm struggling to feel confident in determining the current profile of these batteries (which don't list internal resistance, etc), and thus the trip behavior of the various fuses in such a condition. My present operating assumption is that a true short circuit is going to result in many, many times the continuous current ratings of the batteries, and trip even a moderately over-sized fuse in 100's of ms or even faster. If this is right, I could safely size a single fuse at either 350A (sized for continuous load) or 400A (sized for peak load) without issue. Am I thinking about this right?
My final question is in regard to using a single fuse for the battery bank, vs a separate fuse for each inverter. Given that I want the fuse or fuses contained in the cabinet, the latter would require longer equal-length runs between the cabinet and inverters, and extra cost for the fuses and blocks, but all-in-all a pretty negligible difference in cost if there's a compelling reason for it. Given that the inverters are in a master/slave configuration, I'm not expecting that I could operate with half a system (only 1 fuse tripped), and if I encounter a high-current short circuit situation, the immediate availability of half a system is probably a very small concern. So I'm inclined to go the route of a single fuse.
It looks like I've written a novel. Thanks anybody who bothers reading this! ;-)
- I want to put the fuse inside my rack. Does anybody else do this?
- What is the short circuit discharge current for a 48v EG4 battery?
- I have 2 (coordinated) inverters, should I use a single 400A class T fuse, or two 200A fuses?
Hi all, this is my first post to the forum, but it's already been incredibly helpful.
The existing system...
My wife and I recently purchased a ranch and with it a slightly older but really well designed off-grid solar setup that powers a couple small cabins, well pump, etc.
The system includes two strings of solar totaling 8kW theoretical, but offset directionally so that we get ~5kW max, but solid power throughout daylight hours in winter.
Most components are produced by Outback Power, which includes two Radian GS8048A's set up for split-phase output while also controlling a 9.2kW Stamford generator. Charge controllers are Outback's FLEXmax 80, and the system uses the other components from Radian like the communication hub, load centers, and Mate3.
I had never used their stuff before but have been very impressed! The only thing that is wrong with the system is a surprisingly under-sized and old bank of lead-acid batteries, which now faults when drawing over ~2kW.
New batteries...
Yesterday we ordered four 48V EG4 LiFePOWER's, which is the minimum needed to fully utilize the inverters. We don't yet have a good sense for daily energy needs, since many of the traditionally higher-power loads use propane (stove/oven, water heater, dryer) and we don't live there full-time. The major draws are the well pump and some mini-splits, but so far we've never used much more than ~4kW, and even then not continuously. We almost ordered 6 batteries to fill out the cabinet and provide longer runtime, but decided to play it conservative and potentially save $3k by starting with 4, with plans to add 2 more soon if we find we want them. We don't mind having the generator come on occasionally if needed, but really don't want it running continuously (especially under low [inefficient] load).
Question about fuses...
With the new battery bank, I want to make sure everything's protected from short-circuit loads. My inclination is to think of the cabinet as a self contained and protected system component, so I'd like to put the fuse or fuses inside the cabinet. This doesn't seem to be particularly common here, and I'm curious why? Is there something I'm not thinking of?
RE sizing fuse sizing, I'm working with the following stats from our 2 Radians, each of which list:
- Max Continuous: 8000VA
- Max Peak (30m): 9000VA
- Max Surge (5s): 1200VA
- Instantaneous Power (100ms) 16970VA
The BMS of the EG4 batteries has the following BMS behavior listed under "discharge":
- >100A: 10s
- >150A: 3s
- >250A: 1s
Looking at the blow delay curves of the Blue Sea Class T fuses, it appears that I can safely size the fuses to the "continuous" values of our load without risking it tripping under normal peak/surge/instantaneous conditions. The real purpose is to protect the wiring/BMS from much larger short-circuit loads, though, and so it's presumably important that the fuse trips faster than the BMS. While I've found resources like this, I'm struggling to feel confident in determining the current profile of these batteries (which don't list internal resistance, etc), and thus the trip behavior of the various fuses in such a condition. My present operating assumption is that a true short circuit is going to result in many, many times the continuous current ratings of the batteries, and trip even a moderately over-sized fuse in 100's of ms or even faster. If this is right, I could safely size a single fuse at either 350A (sized for continuous load) or 400A (sized for peak load) without issue. Am I thinking about this right?
My final question is in regard to using a single fuse for the battery bank, vs a separate fuse for each inverter. Given that I want the fuse or fuses contained in the cabinet, the latter would require longer equal-length runs between the cabinet and inverters, and extra cost for the fuses and blocks, but all-in-all a pretty negligible difference in cost if there's a compelling reason for it. Given that the inverters are in a master/slave configuration, I'm not expecting that I could operate with half a system (only 1 fuse tripped), and if I encounter a high-current short circuit situation, the immediate availability of half a system is probably a very small concern. So I'm inclined to go the route of a single fuse.
It looks like I've written a novel. Thanks anybody who bothers reading this! ;-)
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