Bunch'a Questions regarding UPS/Inverters for Solar use

[bhvm]

Dear all,

I am trying to work out a small Solar backup unit. I got the solar part right,I can now charge 2x12v 150AH tall tubular batteries at about 10~11A (In Series) Using a state of the art MPPT solar charge controllers. Now what remains is the UPS/Inverter part. Please provide guidance on the following questions-


1> I have 2 UPS options to use. Both are rated at 800VA. Made by Same manufacturer- Microtek (reputed manufacturer in our area). The Only difference is , One unit runs on 24v (2 batteries in series) and other is 12v Unit.
Surprisingly, the 12v unit is beefier & heavier. Does it mean that 24v units can use smaller transformer for the similar VA ratings? What is the underlying reason. I have modified Both units with fans for added cooling.


2> For this application, I am leaning towards the 24v Unit. As Charging batteries with 24v config appears more efficient. Is that correct?

I have connected the 24v 800va UPS for the moment.


3> There is a slight shock/ Stray current at battery terminals when UPS is ON. Is this normal?
The shocking is not present in 12v Unit.


4> The Lights connected to 24v UPS (On battery mode) Flicker a bit when there is hardly any other load on the UPS. I am using Seoul LED modules with appropriate Drivers & Heatsinks. The Flickering Vanishes when some additional load (Eg a Fan) is started on UPS. What is causing this behavior?

P.s- No Bulging caps in any of UPS visually.

[budm]

Re: Bunch'a Questions regarding UPS/Inverters for Solar use

Some interesting info:
http://www.homemade-circuits.com/p/s...inverters.html
http://www.homemade-circuits.com/201...c-circuit.html

I did not read through them yet to see how correct they are.

12V system will require larger wire gauge than the 24V system to produce the same VA at the output.

'3> There is a slight shock/ Stray current at battery terminals when UPS is ON. Is this normal? The shocking is not present in 12V Unit.' If the charger circuit is not isolated type and has electrical connection to the Line (Primary hot side of the circuit) then it is consider hot circuit, it may also have X/Y cap between the Primary and Secondary side. You need to look at the battery charging circuit.

4> The Lights connected to 24v UPS (On battery mode) Flicker a bit when there is hardly any other load on the UPS. I am using Seoul LED modules with appropriate Drivers & Heatsinks. The Flickering Vanishes when some additional load (Eg a Fan) is started on UPS. What is causing this behavior?
What is the full spec and what is indicated in the user manual with regarding the minimum load requirement for the UPS to operate correctly?

[bhvm]

Re: Bunch'a Questions regarding UPS/Inverters for Solar use

That was quite and in depth read, Budm, The squarewave article is particularly interesting.

I would still appreciate some straight answers though.

[bhvm]

Re: Bunch'a Questions regarding UPS/Inverters for Solar use

'3> There is a slight shock/ Stray current at battery terminals when UPS is ON. Is this normal? The shocking is not present in 12V Unit.' If the charger circuit is not isolated type and has electrical connection to the Line (Primary hot side of the circuit) then it is consider hot circuit, it may also have X/Y cap between the Primary and Secondary side. You need to look at the battery charging circuit.

4> The Lights connected to 24v UPS (On battery mode) Flicker a bit when there is hardly any other load on the UPS. I am using Seoul LED modules with appropriate Drivers & Heatsinks. The Flickering Vanishes when some additional load (Eg a Fan) is started on UPS. What is causing this behavior?
What is the full spec and what is indicated in the user manual with regarding the minimum load requirement for the UPS to operate correctly?

3> I didn't fully comprehend what you said, however it appears true. Perhaps the charger circuit has not as sophisticated and has skipped the "Isolation" part. Apart from the annoying shock, it shouldn't be a problem for the health of batteries or connected MPPT charger, should be?

4> The user manual does not mention anything about the Minimum Load etc. As per my understanding, putting a load of 100w appears to help.
Also, Putting on a Fan/Motor load (even in just 50w) Seems to instantly help.

The Spec of UPS is follows-
800 VA (Double battery)
Over Voltage Protection
Automatic Voltage Regulation
Fuse Protection / Pulse to Pulse Electronic active Protection
Extended Input Voltage Range of 135-300 Volts
Smart Boost function for Low Input Voltage
Smart Buck function for High Input Voltage
Over Load / Short Circuit Protection
Battery Deep Discharge / Over Charge Protection

Extended Input Voltage Range of 145~300 volts : When the voltage fluctuates to as low as 150 volts & as high as 290 volts, these UPS give you the corrected line voltage output of 230 volts ± 9% and don't switch the UPS to "Battery Backup mode" like most other UPS.
Smart Boost function for Low Input Voltage : When the mains voltage is low, the smart boost will correct it back to its normal range without draining the internal battery.
Smart Buck function for High Input Voltage : When the mains voltage is high, the AVR or smart buck will correct it back to its normal range without draining the internal battery.
Over Voltage Protection : The UPS will switch to backup mode and offers power from its internal battery when the mains voltage is too high.
Over Load / Short Circuit Protection : If the UPS is excessively overloaded in backup mode or encounters a short circuit, it will go into protection mode. The output will be shut down in this case and will instantly recover on the removal of this condition.
Battery Deep Discharge / Over Charge Protection : The UPS has in-built electronic protection circuit which protects the batteries from getting deep discharged or over charged.

[Longbow]

Re: Bunch'a Questions regarding UPS/Inverters for Solar use

I got the solar part right,I can now charge 2x12v 150AH tall tubular batteries at about 10~11A (In Series) Using a state of the art MPPT solar charge controllers.

Interesting project. Any photos that you would like to share? Maybe a block diagram of your project?

First, why did you decide to charge the batteries in series? Even with the same battery type, the batteries will never receive equal charging. What is your expected load? How long is the load expected to operate on the 2 batteries?

1>Surprisingly, the 12v unit is beefier & heavier.

For the same VA rating, the 12 volt unit has to handle twice the current. Also consider the efficiency of each UPS unit by itself.

2> For this application, I am leaning towards the 24v Unit. As Charging batteries with 24v config appears more efficient. Is that correct?

Overall system efficiency will depend upon how your batteries take a charge. Series charging is not optimum, so I expect the system efficiency to be lower using 24 volts. Also, the source impedance of 2 batteries in series is higher, even assuming that they are equally charged. External wiring gauge must also be accounted for, since the current in the 12 volt system will be 2x.

3> There is a slight shock/ Stray current at battery terminals when UPS is ON. Is this normal?
The shocking is not present in 12v Unit.

A shock when touching both 24 volt terminals with your fingers? You may not have 24v d.c. but instead a pulse waveform with higher peak voltages. Or, you might have low body resistance.

4> The Lights connected to 24v UPS (On battery mode) Flicker a bit when there is hardly any other load on the UPS. I am using Seoul LED modules with appropriate Drivers & Heatsinks. The Flickering Vanishes when some additional load (Eg a Fan) is started on UPS. What is causing this behavior?

Most likely the UPS needs a minimum load to deliver the specified output voltages at specified output ripple. In your case, why not operate the LED's directly from the batteries? Strip LED's are available in both 12 volt and 24 volt, so drivers are not necessary. Keep in mind that there is a wide range of quality when it comes to LED drivers. [/QUOTE]

[bhvm]

Re: Bunch'a Questions regarding UPS/Inverters for Solar use

Hello Longbow, Thanks for detailed input.
1> I'm using the project since 2 years now. It used to be a 12v system. I had dedicated 12v wires running around the house. However voltage loss in a large house was too much, so I am looking to upgrade 24v inverter and various LED constant current drivers or SMPS for run the loads. That should save me some cabling loss.
+
WIP Pics & Discussions-
http://www.theautomotiveindia.com/fo...me-office.html


2> Expected loads on Inverter are as follows-
*Daytime when I leave to work- 5~20w (used only for Modems, Cordless Phones & Mobile charging)
*Evening 7pm to 10pm- 150~350W (Used for dinner Lights, TV, laptops, Music etc etc)
*Night 10pm to 6am- Max 30w, (Used for street lights, modems & Night lamp)

Street light design-
http://www.instructables.com/id/DIY-...Find-The-LEDs/

Night lamp design-
http://www.instructables.com/id/DIY-LED-Glow-Blocks/

http://www.instructables.com/id/Charming-LED-Flowers/

USB charger-
http://www.instructables.com/id/DIY-...ger-LED-light/

Reading lamp-
http://www.instructables.com/id/Tran...o-2800-Lumen-/



3> Yes the 24v UPS is MUCH more efficient. It consumes 0.3A idle. & Runs Modems, cordless phones at 0.9A battery draw.

4> I don't see series charging a problem, as my solar MPPT supports equalizing overcharge which i use once a month or so. I can also set equalizing voltage as per ambient temperature. Earlier I had 2x 12v batteries connected in Parallel. The charging efficiency wasn't good.

5> The shock is there at either terminal, and only when UPS is ON. The shock dissapears when I press UPS Switch OFF. Thats what I do when adding distill water.

6> As discussed above, I am gravitating towards
Inverter>230vAC>Constant current driver> LEDs

Rather than
12v battery> LEDs

For the reason of Cabling losses and trouble running heavy gague wire 6.0SQMM around the house.

I guess we are playing Tesla vs Edison now!

7> Perhaps. The voltage is all over the place on Idle. It keeps jumping from 190v~260v on DMM. Is that how an Idle should behave?


8> My MPPT solar charge controller is rated at 20Amps. It does not care if its 20A at 12v or 24v. Naturally, charging at 24v system is doubly more effective.


PS- I have connected the 24v UPS since 2 weeks now and its working beautifully. Apart from Idle flicker problem, it has no issues running loads upto 480w (Thats the peak I can use to test with ALL lights, fans, TV on).

I have added a small fan to suck hot air from the UPS.

The 12v Street lights & LED strips have been converted to 12v transformers or CC drivers as required.