El-Cheapo UPS Battery replacement: Can I use Lithium (LiPo)?

supersunbird

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I just cracked open a 2000VA RCT UPS and found two really crappy 12V 4Ah batteries in there.

I replaced those batteries with 12V 8Ah lead crystal batteries, will be interesting to see how it performs now.

Seems that these guys try to save a bit on batteries.

But to RCT's credit, the rest of the insides looked well designed and constructed.

Struggled to find lead crystal batteries for sale.
 

Geoff.D

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I just cracked open a 2000VA RCT UPS and found two really crappy 12V 4Ah batteries in there.

I replaced those batteries with 12V 8Ah lead crystal batteries, will be interesting to see how it performs now.

Seems that these guys try to save a bit on batteries.

But to RCT's credit, the rest of the insides looked well designed and constructed.
Have you got spec for that RCT?
 

Jola

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Last edited:

gertvanjoe

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Don't know what you were doing to your batteries for it to explode, but my ( ignorant ) cousin had this battery in a cabinet blowing up for weeks. He's charger was fvcked.
Got called to go check out a gate motor for someone as a favour, said it started slowing down last week and now works at a crawl. Open the casing and found such a balloon, disconnected it first thing. Measured the charging voltage, 32 f@#Rcken volts, that poor battery was boiling
 

Geoff.D

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Here are some really important facts about the Blue Nova drop replacement batteries to take not of.

Yes, the batteries will give you extend life, and last longer when the mains fails BUT it all comes to nought IF the device you use them in can't charge them properly when power returns. The dangers that the battery will be run down below its minimum voltage is very significant. Most LA battery designed UPs WILL allow that to happen and the battery will not recover after being run flat during load shedding.

The information is courtesy for the Blue Nova.

1. The drop-in replacement is related to the form factor and NOT in relation to the charger/inverter design. Each application has to be checked to ensure that the battery will charge properly after it has been discharged.

2. The BN batteries do have an internal BMS system designed to balance the cells withing the BN battery, NOT to balance the power drawn between batteries. So IF more than one battery is used in a series application to get 24V or more, the batteries MUST be charged in parallel with a suitable battery charger for at least 30 minutes, at the absorption Voltage of 14.1-14.4 Volts and at a current of at least 5A for each battery placed in parallel. This will balance the batteries before they are connected in series.

3. The Charge/ inverter MUST be set to cut power to the load at a voltage of 11.6V. Failure to do so means the battery may not startup and charge after it has been driven down 100% DoD. Then a process is required to get the battery back up and running again which involves switching it off and "equalising the battery".

The equalisation process may mean charging the battery at 14.1- 14.4 V at 5A for 120 minutes.

4. Charger in the device ( UPS etc) must be capable of charging at 14.1 - 14.4 V and a current of 5A for at least 1 hour before returning to a trickle charge mode. This IS the most important aspect of ensuring that the battery will last as long as it is supposed and needs to be checked before just dropping it into any device, UPS, alarms system, gate motor etc. Otherwise, you fork out the price 3 x the LA price and get exactly the same life out of the BN battery and basically score nothing.

5. The float Voltage is ideally 13.9 V. The charger in the device must connect to the battery when the voltage drops to 12.5 V for best performance.

The above should settle and confirm what others' have already posted about what their experience is with these batteries as replacements in existing el-cheapo UPs and eve a few backup devices currently equipped with LA batteries.

In other words guys, this all not as simple as some would believe. Rather get a setup designed for proper backup power using Li batteries than trying jury rig something form units designed for LA batteries unless you are prepared to add external modules and things to existing systems.

Note most alarms systems running off 12V 7AH LA batteries are designed to trickle charge @ 200 - 400 mA, which is way below what is required for Li batteries. So a modification is required to an alarm system when using Li batteries as replacements. Similarly, you need to check out the charger spec in gate motors before making the change.
 

Geoff.D

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For a 20w load you need approximately 1ah of every 15 minutes of backup time (12 / 20 / 2 x 0.85 = hours/ah). So a 7ah battery (like a gate motor or alarm system) will give you 1h45m and a 8ah will give you 2 hours. If you connect 3 batteries in parallel you can comfortably get through a 4 hour load shed. You also get 60ah deep cycle batteries, which would give you 15 hours.

I see no one reacted to this post. So, either we are all geniuses or all of us were too embarrassed to admit that the maths used by @Dairyfarmer is shall we say quite overwhelming. Therefore in the interest of us slobs who were rather bamboozled at the time and maybe still are, here is an explanation of what he was up to.

The calculation he did is based on sound principles.

So maybe there a bit of room to explain it @Dairfarmer if you have no objections I hope :unsure:?

1. Assuming there are no losses and conversion losses, efficiencies and power losses involved then,

a 7Ah, 12V battery will have an energy capacity of 7 x 12 = 84 Wh [Ah x V= A x V x h] = Wh.
2. The load is 20 W
3. So then the run time would be Wh (battery capacity)/W (load) = Rt (hours); 84/20 = 4.2 Hours,
IF the battery is completely discharged to 100% DoD.

4. Now IF you want to only discharge to the battery to 50%, then the available Capacity would be
84/2 = 42 Wh.
Then the Rt would be 42/20 = 2.1 hours.
{50% of battery capacity[Wh]/load [W] = Rt [hrs]}

5. If you now assume that all the losses etc mean that 15% of the capacity would be lost,
then only 85% of the capacity will be available to drive the load.

ie 42 [Wh] x 85% / 20 = Rt = 1.785 hours = 1h 47min.

6. For a 20w load you need approximately 1ah of every 15 minutes of backup time (12 / 20 / 2 x 0.85
The line at the top, therefore, is a shortcut calculation designed to confuse the masses that allows for both a 50%DoD and a loss allowance or efficiency of 85% and comes up with hours required per battery Ah.

12 [V] / 20 [W] x 50% DoD x 85% [efficiency] = 15.3 minutes/Ah

7Ah = 7 x 15.3 = 1h 47.1 min ( rounded to 1 h 45min, to confuse the masses some more)


:unsure: :D
 
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SDM

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I’m looking to replace my SLA as the current one is busy dying again after 12 months and am considering a LiFePo4 replacement like the BlueNova with a built in BMA.

My setup draws 6A from a 100Ah battery when the power is off, which is fine for loadshedding stints. However, with Tshwane power supply being so unpredictable these days, it has become hard to manage the battery discharge levels. I have experienced several outages in the past few months ranging from 5 to 19 hours.

I found this informative article on charging a LiFePo4 battery, including some advice on using an SLA charger. In summary, they can be used on a properly designed SLA charger within certain limitations. The compromise will be reduced battery life due to constant float charge being applied.

Power Sonic - how to charge LiFePo4 batteries
 

Jola

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I see no one reacted to this post. So, either we are all geniuses or all of us were too embarrassed to admit that the maths used by @Dairyfarmer is shall we say quite overwhelming. Therefore in the interest of us slobs who were rather bamboozled at the time and maybe still are, here is an explanation of what he was up to.

The calculation he did is based on sound principles.

So maybe there a bit of room to explain it @Dairfarmer if you have no objections I hope :unsure:?

1. Assuming there are no losses and conversion losses, efficiencies and power losses involved then,

a 7Ah, 12V battery will have an energy capacity of 7 x 12 = 84 Wh [Ah x V= A x V x h] = Wh.
2. The load is 20 W
3. So then the run time would be Wh (battery capacity)/W (load) = Rt (hours); 84/20 = 4.2 Hours,
IF the battery is completely discharged to 100% DoD.

4. Now IF you want to only discharge to the battery to 50%, then the available Capacity would be
84/2 = 42 Wh.
Then the Rt would be 42/20 = 2.1 hours.
{50% of battery capacity[Wh]/load [W] = Rt [hrs]}

5. If you now assume that all the losses etc mean that 15% of the capacity would be lost,
then only 85% of the capacity will be available to drive the load.

ie 42 [Wh] x 85% / 20 = Rt = 1.785 hours = 1h 47min.

6. For a 20w load you need approximately 1ah of every 15 minutes of backup time (12 / 20 / 2 x 0.85
The line at the top, therefore, is a shortcut calculation designed to confuse the masses that allows for both a 50%DoD and a loss allowance or efficiency of 85% and comes up with hours required per battery Ah.

12 [V] / 20 [W] x 50% DoD x 85% [efficiency] = 15.3 minutes/Ah

7Ah = 7 x 15.3 = 1h 47.1 min ( rounded to 1 h 45min, to confuse the masses some more)


:unsure: :D

Yep, and similar logic applies to alarm systems, etc.

This is why the 4 to 5 hour loadshedding periods in Johannesburg are just not acceptable, none of the UPS's, gate motors, alarms, etc, can handle those periods without the batteries suffering damage, even with new batteries.
 

Geoff.D

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Great post! Thanks for sharing.
I’m looking to replace my SLA as the current one is busy dying again after 12 months and am considering a LiFePo4 replacement like the BlueNova with a built in BMA.

My setup draws 6A from a 100Ah battery when the power is off, which is fine for loadshedding stints. However, with Tshwane power supply being so unpredictable these days, it has become hard to manage the battery discharge levels. I have experienced several outages in the past few months ranging from 5 to 19 hours.

I found this informative article on charging a LiFePo4 battery, including some advice on using an SLA charger. In summary, they can be used on a properly designed SLA charger within certain limitations. The compromise will be reduced battery life due to constant float charge being applied.

Power Sonic - how to charge LiFePo4 batteries
 

newby_investor

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Yep, and similar logic applies to alarm systems, etc.

This is why the 4 to 5 hour loadshedding periods in Johannesburg are just not acceptable, none of the UPS's, gate motors, alarms, etc, can handle those periods without the batteries suffering damage, even with new batteries.
Indeed. I've always wondered why they do that, unlike Cape Town which does 2 hours.
 

newby_investor

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Nevermind the extra stress on substations allowing them more time to cool and burst into flames.
Transients are the only thing I can't really think of justifying four hour blocks instead of two hours. They'll have less switching things on and off. But it seems a stretch to me still.
 

Jola

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Transients are the only thing I can't really think of justifying four hour blocks instead of two hours. They'll have less switching things on and off. But it seems a stretch to me still.


Yep, whatever the reason, Joburg CC is doing it.

IMO they are trying to shift the damage that results from rolling blackouts onto the consumers, instead of being responsible for it themselves.

I'm going to have to spend some R10k on new batteries, that I'm quite sure would have lasted for another few years with 2 hour blackouts.
 

thehuman

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I’m looking to replace my SLA as the current one is busy dying again after 12 months and am considering a LiFePo4 replacement like the BlueNova with a built in BMA.

My setup draws 6A from a 100Ah battery when the power is off, which is fine for loadshedding stints. However, with Tshwane power supply being so unpredictable these days, it has become hard to manage the battery discharge levels. I have experienced several outages in the past few months ranging from 5 to 19 hours.

I found this informative article on charging a LiFePo4 battery, including some advice on using an SLA charger. In summary, they can be used on a properly designed SLA charger within certain limitations. The compromise will be reduced battery life due to constant float charge being applied.

Power Sonic - how to charge LiFePo4 batteries
Charging could get yourself a victron smart charger , 12v or 24v system ?
 

Geoff.D

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Are there any 1kVA - 2kVA UPS that come with Lithium batteries instead of lead acid?
Yes there are but typically 3 x the price because of the batteries used. But now, a far better buy.
 

ginggs

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Yes there are but typically 3 x the price because of the batteries used. But now, a far better buy.
Do you have any links please?

Three times the price for batteries that potentially last five times longer is not a bad deal!
 
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