You can do this by using a high wattage 100 ohm resistor on either the positive or negative side of the battery just long enough to get them charge and reduce the chance of a massive inrush voltage. Regarding the capacitors - never just hook the battery up to the UPS (or inverter for that matter) without recharging the caps. The BMS (if you're building your own pack as I am) can be programmed for cut off voltages and currents to protect the cells, but again as pointed out USE A FUSE or high quality breaker inline with the battery! Bottom line, it is doable. The BMS will also cut off at 2.5V/cell - 20V for the pack if the UPS hasn't cut off before that point. At 27.35V that gives you 3.42V/cell, which is at a pretty good point for maintaining the batteries. Each LiFePo4 cell can take unto 3.65V, but you'll want to charge to a lower voltage to extend life. I just checked the voltage on my APC 1500 and it is about 27.35 volts. But as was pointed out LiFePo4 are more tolerant (and much safer) than Li-Ion to various charging voltages. The answers that reference Li-Ion are accurate, I wouldn't ever use Li-Ion with a charger that is designed for Lead Acid. The drop-in BMS has to also manage the lithium-based battery cut-off voltage independently of the UPS cut-off voltage, so it has to be smarter than the average charge-only BMS. Accordingly, the output of a lithium-based battery isn't going to match precisely the UPS VRSLA figures, but that's less of a factor, generally speaking, as such devices are supposed to handle 13.x down to about 10.x volts. The OP would have to discover a drop-in lithium pack that is designed to accept either 13.x or 26.x volts (typical VRSLA charging level) and adjust it to the native/healthy levels required of the lithium pack. The drop-in version would accept the voltage and massage it to keep the lithium battery comfortable. For example, in a conventional motor vehicle, the alternator can be expected to provide 14.1 vdc, which would cook a lithium battery in short order. One would expect that a drop-in replacement has at least the charging portion and has tailored it to expect the input voltage and current for the device in which it is installed. Some of them regulate charging and discharging, others manage only the charging aspect. This is not going to work within a UPS unit, which charges based on the lead acid profile.īMS terminology can be somewhat misleading. Consider to edit your question to include a product link.Īll of the search results I've pursued for this type of product (specifically 24v lead acid replacement) have text indicating that a lithium rated charger is to be used, not the lead acid charger. If your battery presents itself as you suggest, it's possible you've found such a drop-in replacement. They typically have circuitry that manages the charge profile for the new chemistry. However, there are battery replacements that are advertised as "drop-in" matches for lead-acid versions. The answer based on the information provided is NO.
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