Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 85 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings.
Full specifications: OutBack VFXR3648A and SimpliPhi PHI 3.8.
The four checks
Voltage window: Overlapping window 44 to 57.6 V
The inverter operates from 40 to 64 volts and the battery cuts off outside 44 to 57.6 volts. Both stay inside 44 to 57.6 volts, which covers a normal LiFePO4 charge and discharge cycle with margin at both ends.
Charge current: 85 A into a 150 A limit
The inverter tops out at 85 amps and the battery accepts 150 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.
Surge rating: Battery surge figure unpublished
A surge to 7200 watts draws roughly 150 amps at 48 volts. This battery publishes a 150 amp continuous rating and no separate surge figure, and continuous is the wrong number to check a motor start against. Confirm the peak rating and its duration with the manufacturer before running motor loads.
Closed-loop communication: Battery publishes no protocol
The inverter speaks Modbus. This battery publishes no communication protocol, so closed loop is not on the table and the pairing runs on voltage limits set by hand. Confirm with the manufacturer that no port exists before assuming it.
What this means when you install it
Set the inverter charge current to 85 amps or less. That is the inverter maximum, which this bank can absorb. Protect the battery run with a 100 amp Class T fuse and 2 AWG cable wired to a busbar rather than daisy chained, so all 2 packs share current evenly.
The inverter speaks Modbus. This battery publishes no communication protocol, so closed loop is not on the table and the pairing runs on voltage limits set by hand. Confirm with the manufacturer that no port exists before assuming it.
Figures side by side
| Field | OutBack VFXR3648A | SimpliPhi PHI 3.8 |
|---|---|---|
| Voltage window | 40 to 64 V | 44.0 to 57.6 V |
| Charge current | 85 A delivered | 150 A accepted (2 packs) |
| Peak draw | 7,200 W surge | surge unpublished |
| Usable capacity | n/a | 7.6 kWh (2 packs) |
| Comms | Modbus | none |
Manufacturer documents
Manufacturer documents: OutBack Power documentation. Figures here should be read against the revision that covers your serial number, because manufacturers revise specifications without changing the model name.
SimpliPhi has no public document library this site has been able to verify. Every figure on this page therefore needs checking against the paperwork that shipped with your unit.
Both units, current pricing
Prices on these move week to week, and the battery is usually the line item worth watching.
OutBack VFXR3648A on AmazonSimpliPhi PHI 3.8 on AmazonComms cableAffiliate links. As an Amazon Associate this site earns from qualifying purchases, at no extra cost to you. Prices and stock change often, and a listing appearing here is not a statement that the pairing above is approved.
Other pairings for the SimpliPhi PHI 3.8
EG4 6000XP with SimpliPhi PHI 3.8
Partial match, some fields unverified.
EG4 18KPV with SimpliPhi PHI 3.8
Partial match, some fields unverified.
EG4 FlexBoss21 with SimpliPhi PHI 3.8
Partial match, some fields unverified.
Sol-Ark 12K with SimpliPhi PHI 3.8
Partial match, some fields unverified.
Questions people actually ask
Will the OutBack VFXR3648A work with the SimpliPhi PHI 3.8?
Partial match, some fields unverified. Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 85 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings. The four checks below show which field produced that result.
What does this pairing cost to wire up?
Beyond the two units, a 100 amp Class T fuse and holder, 2 AWG battery cable cut to matched lengths, and a busbar if you are running 2 packs. A comms cable if you intend to attempt closed loop, and the pinout is rarely the same between brands.
Where does this pairing go wrong in practice?
The inverter speaks Modbus. This battery publishes no communication protocol, so closed loop is not on the table and the pairing runs on voltage limits set by hand. Confirm with the manufacturer that no port exists before assuming it.
What charge current should I set?
The inverter tops out at 85 amps and the battery accepts 150 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.