Notes Regarding Building a PriUPS using an APC SURTD5000XLT

Copyright Last updated on 10/23/2012

WARNING: The voltages and currents described in this website can cause injury or death. This website does not contain professional advice. This website is purely intended for informational and educational purposes. No guarantee is made that the information is up-to-date or currently accurate. I am not a licensed electrician and the information on this site does not purport to be a legal interpretation of any code or law. The information is presented to highlight some issues that one might want to consider. Always seek professional advice as needed or required by your locality.

Note that this is a work in progress. This page is not complete. More to come as the project progresses.


The idea is to use one of our Priuses to act as a backup power source in the event of a day or multi-day power outage. Since our house uses a well for water, a power outage also means no water. The common cause of extended power outages in this area are ice storms. In rare cases, the outage can last for several days. The inspiration for this idea comes from Richard Factor's excellent website This implementation is nearly identical to that of Doug Gaede .

UPS Selection


I was able to purchase a SURTD-5000XLT for a reasonable price from Weisscopower on EBay. The unit was shipped via a freight service and arrived quickly and safely. The unit is listed as refurbished (with new batteries.) Overall, I was quite pleased with this purchase. The particular EBay listing had listed it as a SURT rather than a SURTD model. The SURTD is a newer model, but some may prefer a SURT if they are using the Network UPS Tools. The SURTD models now use a proprietary interface that is not currently compatible with this software. I am in the process of testing the unit before I proceed with a Prius hookup.

Your mileage may vary, but the particular unit I received did not have a Network Management Card. I was able to acquire a Network Management Card for a reasonable price on EBay.

The SURT(D)-5000XLT units can output 208Vac or 240Vac. However, they do not have a neutral so a SURT003 Isolation Transformer is required to output 240Vac/120Vac for home use.

More to come.

AP9617 Network Management Card

I acquired an AP9617 Network Management Card. I initially had trouble communicating with the card and the card did not recognize it was connected to a UPS. To make a long story short, after updating the firmware on the card everything worked. The card provides a nice web interface to access the status of the UPS and to change parameters such as the operating voltage.

SURT003 Isolation Transformer

This transformer is able to convert 208 Vac or 240 Vac into 240 Vac and 120 Vac. It should be noted that as built, the unit I received has the neutral and ground bonded together. One implication of of this is that by my (miss-)interpretation of the National Electric Code (NEC), the unit might be considered a "seperately derived source." As such, it would require if connected to a transfer switch, one that also switches the neutral line. Simple load side transfer switches generally do not switch the neutral line. In any event, the NEC requires that the neutral be bonded to the ground at only one location within the entire system.

Here is a view of the components inside of the SURT003. The major item is a huge heavy torroidal transformer. The other item is a control and distribution board that powers the fans and distributes the power.

Here is a close up of the control and distribution board. Notice the screw in the center that has been circled in red. It is this screw that serves that serves as the single point to bond the neutral to the ground for the system. The screw is electrically connected to the board and to a standoff that is welded to the case. The board also electrically contacts the standoff. In theory, the unit could be converted to a floating neutral system by using insulated standoffs for the control and distribution board in order to remove the bond. Care would need to be taken to insure adequate isolation. A floating neutral would be useful to allow the use of a simple load side transfer switch. However, if the bond were removed, the unit could not be used as a stand alone unit not connected to the transfer switch. To be safe, the neutral must be bonded to ground at some point in the system.

APC Battery Connections

The APC battery connections are Anderson Power Pole SBS50 connectors. The specifications on these connectors can be found at These connectors are available from Mouser. These are very interesting connectors with several features that make them ideal for this application. First they are finger safe and hot pluggable. The connectors are unisex couplers so any two connectors can be joined together. The connectors are mechanically keyed and identified by color so only connectors of the same color can be interconnected. Anderson Power Products recommends that the brown connectors be used for 96 V applications and the white connectors are for 192 V applications. These are the color assignments used on the APC SURTD5000XLT UPC.

Alternative Options

An alternative is to use a DC to Dc converter to convert the Prius High Voltage to that used by a battery bank. Then use a traditional battery powered inverter to generate the AC. Batteries are optional but can be used to supply extra power during start up surges if needed. This concept is basically that documented on PriUPS Bonus: Multiple Supply Examples.

DC To DC converters

In additon to the versions documented on PriUPS Bonus: Multiple Supply Examples, I have found that Meanwell makes ac/dc converters that are specified to also support dc/dc conversion. Several models use 127--370 Vdc inputs (as well as 90--264 Vac) so seem ideally matched for use in the Prius. DC output voltages are available for 12, 24, (sometimes 27,) and 48 V. Note that for this use, it appears that the output overload protection is the other critical item. Current limiting without shutdown is needed. Only a few models in a few series have both the desired voltage range and the desired overload protection.

From my quick look, it appears that candidates include (xx is the desired output voltage):

RSP-1000-xx 1 kW and active current sharing for up to 4 units for 4 kW (Higher power units in this series either shutdown on overload or take a higher input voltage than desired i.e., 254--370 Vdc
SPV-1500-xx 1.5 kW and up to 3 unit current sharing for 4.5 kW

Two other interesting items are chargers that can take the Prius voltage and charge a battery bank, namely PB-600-xx and PB-1000-xx which are 600 and 1,000 W chargers that can be used for power at the same time as in a UPS.

Meanwell also makes a 3kW inverter that appears to be UL listed.

For those who are interested, I have noticed that Meanwell products are available from Jameco and Mouser (but not at the time of this publication at Digikey) I have found another source with more competitive prices in PowerGate LLC.