16 SLAs in series - typical UPS set up

MarkC

My "PriUPS" system consists of an APC SURT6000 and a SURT003 isotransformer.  The SURT6000 uses 16 - 5.5 Ahr, 12 V SLA batteries in series to power the back up energy (out of the box).  I've logged hours of data with this system with the Prius supplies energy only.  The voltage cycle is quite consistent at 7-8 minutes round trip with the lowest being ~200 VDC and the highest at ~245 VDC.  With wattages from 1200 to 4200, the cycle basically drains faster and rebuids slower, but the overall cycle time remains about the same (likely a function of the traction battery condition, which for my 2012 Prius is likely not good).

I've been reluctant to keep the standard battery packs hooked up during the use as a back-up gen system as I'm not sure if the SLAs will be damaged by this cycling voltage.  

Question is can the OEM SLAs be left in place for a short period of time without damage (maybe a couple of voltage cycles) - or could they be left hooked up for quite a long time with such a voltage cycle (not really necessary, but just wondering).

BB.

Mark,

You mean the 16x SLA batteries in parallel with the Prius battery pack?

The voltages (ref 12 volt standard):

• 245v/16 batteries = 15.3 volts
• 200v/16 batteries = 12.5 volts

Those batteries are not really being cycled much (assuming 12.7-12.8 volts is "full" and 200 VDC is measured "under load")... So, mostly just taking off surface charge/going from EQ to low Float charging (sort of)...

The battery mfgs always seem to say any "discharge" is a cycle--So even going from 12.8 to 12.5 volts is a "shallow cycle". Batteries that are "shallow cycled" do have more cycle life... Say yours is 25% discharge vs 50% cycle--That is typically approxmatly 2x longer cycle life to 25% depth of discharge vs 50% depth of discharge is "less bad" for the batteries--But still a cycle.

Small SLA batteries for UPS are generally "float rated"--Long life at 13.6 volts or so, and only a hand full of discharge cycles to maybe a few hundred discharge cycles (probably assuming to 50% or lower State of Charge)...

Between the relatively low cycle life for typical UPS SLA batteries, and charging to ~15.3 volts (albeit for short periods of time) is not great for the batteries... Watch their temperature and (if you can) check the electrolyte levels/bubbling/gassing.... If they get hot, bubble, or vent, then I would probably avoid using the SLA with the Prius battery bank.

Why are you interested in connecting the SLA bank--Longer engine cycles (longer off, longer on) and "easier" on the motor with fewer start/stop cycles? I don't know that you will save much fuel usage with 18 minute cycles vs 9 minute charge/discharge cycles...

But this is always the tradeoffs... Using your Prius for emergency backup power. Have you looked at fuel consumption (kWH per Gallon of fuel... maybe 3-5 kWH per gallon for a Honda eu2x00i genset or similar)? Get a second Prius battery back from a junkyard to increase capacity?

-Bill

MarkC

Thanks as always Bill.
This is the scenario that would use the SLAs in parallel with the Prius traction battery:
- Weather forecast is indicating that an extended power outage is a good possibiity due to a hurricane, bad storm, deep freeze (not likely to ever happen again in Texas).
- I'd start up the UPS on its battery pack under power.  
- Prius prepared with full tank and the extended cable hooked up in the trunk
- If power goes out, the SURT unit is running on the SLAs - no real load, so it will run for probably an hour or more - hopefully enough for me to get home and start up the Prius.  The point being that the SURT is running - no inconsistent "black start" is required - I've had this issue with this unit.
- As soon as possible, I'll hook up the extended cable to the SURT and start up the Prius for back up power - Hook up my fridge and a few other users with extension cords on the SURT003.
- within a few minutes, maybe a cycle or two at the most, I'll disconnect the SLAs and run soley on the Prius battery.

I can't see a reason to continue to run the SLAs once the Prius is hooked up, but just curious if running them in parallel for a more extended time might be harmful.  They don't have enough kWh to help the Prius much, so no real need.

Someone did a fairly rigorous test on his PriUPS system and he reported that fuel consumption was similar to the Honda EU2000.  I don't have any confirmation.  Of course, at the full load of 4200 watts, I'm sure the fuel consumption is higher due to the increase motor- on cycle time.  I don't plan on using the full load for any extended time - likely less that 1000 watts continuous.  

BB.

I would be a bit weary of connecting a Prius battery pack in parallel with discharged Lead Acid pack--You could see some (relatively) heavy currents as the two battery banks equalize. Without details (or testing) if the Prius is around 245 volts and the SLA bank at (16*12.0v under load = ) 192 volts--Don't know what could happen.

Ran 2x full size modern refrigerators and 1x modern freezer, plus ~500 Watt pond pump on an eu2000i for around 2.5 gallons per day or so... The eu did fine--But it was close on running all those loads at the same time (was brand new, had to break in for 10+ hours before could run on ECO throttle and start a random fridge).

Used the "gas cap siphon" method to draw fuel from 5 gallon gas cans (eu2x000i and similar small gensets can draw fuel from fitting in gas cap to refill main tank--Or keep it full--The small genset fuel pump can draw enough of a vacuum in the main genset tank to pull the fuel across).

-Bill

MarkC

You are spot on with my concern about the possible heavy arcing during hookup of mismatch voltages and/or some possible battery damage.  In the tests that I've run so far, my Prius battery voltages upon hookup are at the low end - around 210 VDC - but limited data.  Appears I need to do some more "experiments" before feeling comfortable with the "black startup" routine.  The SURT is a double conversion unit with settings of 240 VAC and 60 cycles, so I don't know why I've had problems with consistent "black starts".   As I enjoy these types of experiments - what the heck!
Appears a much easier solution to a limited back up power is a good gen set!  I'd guess if fuel capacity was the bottom line concern, use my gas tank siphon!  Again, I'm retired and enjoy such "experiments" anyway.