Paralleling Different Capacity AGM Batteries

[Delmar]

I am installing a UPS to run my Moms TV and satellite dish during short-term grid down. Measured around a 100W draw. The backup system needs to be granny-proof autonomous so have already purchased a APS sine wave BR1000MS. Cost $160 with tax & shipping and should receive next week.

The UPS is supplied with an internal 24V AGM Battery rated 130VA. Per the UPS specs the 100W draw should only run for 43 minutes. I plan to replace the internal batteries with a pair of external 35AH Harbor Freight AGM in series, cost will be $117 for the pair after my 20% coupon. Capacity @ 24V = 840VA. With the 100W draw should run 4.6 hours.

The batteries will be in float 99.99% of the time so I am not concerned with reduced cycle life from overly discharging the batteries. Our last rolling blackout lasted three hours.

Question: how bad of an idea would it be to parallel the internal 130VA battery with the external 840VA battery? Would give me 970VA and 5.3 hours runtime. The 130VA battery is already included and I have no other use for it.

 

[snoobler]

VA is not a battery rating. It's an alternate expression of Watts.

Most UPS are not duty cycle rated for long durations of inverted power. Adding/replacing batteries of substantially higher capacity may cause premature failure. If you don't care that it only works a handful of times. Additionally, the existing battery takes 16 hours to charge. A larger battery might take 5 days to charge.

https://www.amazon.com/Tripp-Lite-PowerVerter-APS750-connector/dp/B00JPRJ348 + a 12V of your choosing would provide the same function

750W PowerVerter APS 12VDC 120V Inverter/Charger with Auto-Transfer Switching, 2 Outlets | Eaton

Delivers clean 120V AC power from AC or DC power source 750W continuous output power; 1500W peak power Auto-transfer switching option for UPS operation Protects against blackouts, surges and EMI/RFI line noise Rugged polycarbonate housing resists moisture and impact

www.tripplite.com

" Auto-transfer switching option for UPS operation "

 

[Delmar]

Thanks for the responses. Any response if I could/should parallel the different batteries?

VA is not a battery rating. It's an alternate expression of Watts.

That's the only rating I could find for the UPS internal battery so based for my calcs. And I should have wrote VAH.

Most UPS are not duty cycle rated for long durations of inverted power.

Understood but I am only loading to 17% of its 600W rated capacity. Will add cooling if required.

Adding/replacing batteries of substantially higher capacity may cause premature failure. If you don't care that it only works a handful of times.

Did it successfully twice with my 12V 36W (edit) Belkin UPS using the same Harbor Freight battery, and my 48V 2700W APC using my golf cart FLA set.

Additionally, the existing battery takes 16 hours to charge. A larger battery might take 5 days to charge.

The batteries will float 99.99% of the time so am in no hurry. Otherwise I plan to purchase lightweight Windynation panels for my golf cart and will repurpose the existing HQST panels for her system.

Thanks for the info on the 750W PowerVerter. Never new it existed, could have been a better choice.

 

[snoobler]

If paralleling the same chemistry, should be fine.

 

[Delmar]

Thanks!

FYI the 750W PowerVerter is not pure sine. Would not want to damage her electronics.

 

[eXodus]

I've got an external AGM on my UPS for years. No issues, but I only run a tiny load.

What you might have not considered is - the battery is not your problem. The UPS will handle them just fine.
The issue is the extended runtime - those cheap UPS are not designed to run unlimited time. They don't have any fans or big heat sinks

They are designed with the internal battery power in mind and not more. So before you give it to Granny, hook up the big battery, put in the expected load and draw it down until it shuts of.

Stay with it!! It might get warm and potential melt or burn.

 

[Delmar]

I am hoping that 17% is also a tiny load and will prevent meltdown. The APC has pretty good protection however I will torture test at my home before transferring to hers.

And its not the cheap(est) APC which is modified sine, the one I purchased is pure sine. Fingers crossed...

 

[Delmar]

There she is in all her glory. Pictured for size comparison is one of the two Harbor Freight 420WH (35AH each) batteries next to the APC pair at 130WH (5.4AH each).



I so want to take it apart and see whats inside, however I cannot even reinstall the battery cover which is intended to come off ?

 

[Delmar]

If you are interested in my test results see Show & Tell