24V Battery back up

Thread Starter

bowlingo

Joined Jun 29, 2011
162
Hi all,

I currently have someone coding and mapping the I/O's for one of these..

http://www.mikroe.com/eng/products/view/419/picplc16-v6-plc-system/

It will end up being 2 of the above connected together due to the amount of inputs and outputs that are needed and will have a GSM controller on the main board.

I need to put some kind of a battery back up on the system so that when the 230V supply has a power cut it will keep the boards running and trigger an input thus sending a txt message telling the user the power has been cut.

The way as I see it this would work is if there is a 24V battery of which is continuously being charged and the boards are run from this battery. Once the 230V source goes open circuit it will then trigger a relay and close an input but not be effected by the power loss due to the system running from the battery all the time?

Another possible way would be to have it so it runs from its 24V power supply all the time then if the supply drops it will engage a battery and at the same time trigger the input.

A UPS might be an option but they seem very expensive?

Thanks
 

K7GUH

Joined Jan 28, 2011
190
I run all my critical radio equipment on a heavy duty battery. Ahead of the battery is a PowerGate unit from West Mountain Radio and ahead of that is a conventional mains to battery charger. The system fails if and only if the battery fails. My system is all 12 volt, but I'll bet there is someone in this galaxy that manufactures similar devices for 24 volts.

If you are interested in a cheap implementation, a simple relay might suffice if your system can tolerate being without power for the time it takes to transfer from power supply to battery.
 

ifixit

Joined Nov 20, 2008
650
Hi bowlingo,

The best solution is to just buy something that just plugs in and works. However, if you want to challenge yourself...

What input voltage can the PICPLC16 board tolerate?

What kind of battery? What is the load current?

Using diodes, you can OR the two power sources together and feed the load. The mains voltage source should be the highest voltage so as to allow for charging a battery to its fully charged float voltage. It can then be on standby to take over if the mains source fails. This method (figure 1) allows for easy battery removal for maintenance.

Alternately, you can just attach your load directly to the battery on float (no diodes). In this case the battery is usually required to be connected all the time. The system can be shut down for maintenance if this is allowed. This method may require a more complex charger.

Regards,
Ifixit
 

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Thread Starter

bowlingo

Joined Jun 29, 2011
162
Thanks for your replies.

I think the way forward is to have the PICPLC running from a small 24V battery (yet to find one) the PICPLC current is very low. Have the battery being permanantly charged (not sure how safe this is) Once the charger circuit disconnects it will then continue to run off the 24V battery but trigger a NC relay of which will trigger an input on the PICPLC so the user can recieve the text message "POWER SUPPLY FAILED"

Anyone further ideas on this?...It should be easy enough to do its just finding the 24V small battery, good quality and safe charger and the relay of which might have to be 24V or if put across the chargers supply circuit 230V?

This is an expensive system £3K in total to build so its going to have to be as reliable as possible.

Thanks
 

strantor

Joined Oct 3, 2010
5,329



The 230V relay is normally held closed as long as mains voltage is present. Then the mains drops out, the relay opens and the PLC signal goes through the normally closed contact and back to the PLC input. The trickle charger you can get from an auto parts store for cheap. The diode probably won't be needed, but I put it there just in case the trickle charger starts to act as a load when mains is removed (not likely).
 

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Thread Starter

bowlingo

Joined Jun 29, 2011
162
Hi all...

I had a chat with the guy who is coding the 2 x PICPLC's today..

If PICPLC one is run from a continuously charging 24V battery and PICPLC two is run using a 24V power supply. If the whole power supply cuts off it will cut the supply to PICPLC two and PICPLC one will detect it is no longer comunicating with it and send out the custom text message "POWER SUPPLY LOST"

I hope the above makes sense..

I am concerned about the reliability of the battery as PICPLC one will be running from a continuously charged battery.

The power consumption of the PICPLC that will be running from a battery is 120mA with all modules off...technically all or most will be off so going on the side of safety I would say it draws 200mA and I need it to remain powered for around 24 hours..I am not sure how to calculate the 24V battery rating I would need?

What I now believe I need it a 24V small battery and a charger than can be permanantly connected to a 230V supply?

Thanks
 

Thread Starter

bowlingo

Joined Jun 29, 2011
162
Had a look on the net and according to my calulcation to get 200mA to run for 24 hours would be 0.2 Amps x 24 hours = 4.8 AH

I have found this 24V 6AH scooter battery

http://www.ebay.co.uk/itm/24v-6ah-Sea-Scooter-Battery-New-L-K-/110811431052?pt=UK_SportingGoods_Scuba_SnorkellingEquipment_SM&hash=item19cce0408c

There are various 24V scooter battery chargers on Ebay of which range from 1A - 5A and the price varies a lot here is a 1.6A affordable one

http://www.ebay.co.uk/itm/24V-MOBILITY-SCOOTER-LATEST-SMART-BATTERY-CHARGER-UK-/180715170331?pt=UK_ConsumerElectronics_Batteries_SM&hash=item2a1376aa1b

I am wondering if a 1.6A charger is powefull enough?...When the unit is powered from the mains does it mean it will be using the 24V from the charger or it will be draining the battery then the charger automatically tops the battery up?

Thanks
 

bwack

Joined Nov 15, 2011
113
...
I am concerned about the reliability of the battery as PICPLC one will be running from a continuously charged battery.
It is a very important thought.
You linked to a battery charger tha will quickly recharge a scooter battery. Remember, you want long-term use with conditioning _and_ quick recharge when needed. Therefore I would have the battery in standby mode with a dedicated charger that is made particularly for the battery technology you choose. The battery on ebay in your link looks like a SLA (Seal Lead Acid). Thats fine for long term use. They are not so fine for continuous cycle charging. You said something about £3000 pound /reliable system. Get a commercial available SLA battery, and a long term SLA charger. To calculate the Ah, remember to be able to have x Ah at the end of the warranty, you should select a x*1.25 Ah battery (4.8Ah * 1.25 >= 6 Ah), well you did this allready :)

I learned alot from this document when working for with PSUs for a IT equipment manufacturer a couple of years ago. They (and other PSU vendors too) have PSUs with Power OK warning signal that will give you time to switch from the PSU to a second power source before the DC drops. Unfortinuatly you must select a >100W to get that feature and I think maybe its a bit overkill, anyway.

http://www.xppower.com/pdfs/techguide.pdf
See pages:
- batteries 14-22
- Status Signals and Controls: page 50 (power ok/ac ok)
- DC Standby Systems: page 59

Edit you may also want to see this thread: http://forum.allaboutcircuits.com/showthread.php?t=40131
 
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Thread Starter

bowlingo

Joined Jun 29, 2011
162
Hi..

Ive had a read of above link and as you said it looks like I am after a 24V SLA battery...My problem is now a charger that I can easily put on it. There are not many 24V batteries around so I might have to get 2 x 6AH 12V batteries and wire them in series so the voltage will increase to 24V and I will still get 6AH out of them.

So this would mean I still need a 24V charger of good quality that will charge at the correct rate?

Does anyone have further ideas on this i.e links to specific batteries and chargers so I can order the bits and get this prob sorted?

Thanks
 

Thread Starter

bowlingo

Joined Jun 29, 2011
162
Just had a look at the tech specs of these batteries

http://www.gnhealthcare.co.uk/images/documents/datasheetnpseries.pdf

These are the chargers that are by the same manufacturer...any ideas which one would be best for my application?

Features​
Micro processor controlled
Short circuit protection
Reverse polarity protection
igh temperature protection
Soft start current control
Fast constant current bulk charge
3 stage charging CI-CV-float
Constant voltage float/standby
Proportional timing
Flexibility, to match battery specification.​
Standard Range​
YCP03A12 300mA 12v
YCP03A24 300mA 24v
YCP03A6 300mA 6v
YCP06A12 600mA 12v
YCP06A6 600mA 6v
YCP1.5A12 1.5A 12v
YCP1.5A24 1.5A 24v
YCP1.5A6 1.5A 6v
YCP10A12S 10A 12v
YCP1A12 1A 12v
YCP1A6 1A 6v
YCP2A12 2A 12v
YCP2A24 2A 24v
YCP2A6 2A 6v
YCP3A12 3A 12v
YCP4A12 4A 12v
YCP6A12S 6A 12v
YCP8A12S 8A 12v​
YCP8A24S 8A 24v
 

Thread Starter

bowlingo

Joined Jun 29, 2011
162
It might be best to charge each battery separately. Charging series connected batteries can overcharge one of them.

The charger at this link can charge 2 series connected batteries at once.
http://www.batterystuff.com/battery-chargers/24-volt/gel-cell/GU2607A.html

Regards,
Ifixit
Judging by the price of that charger I think it would be best for me to get a 24V battery...Although as I see it if you have 2 x 12V batteries and connect the + of one battery to the - of the other battery then have it charging using the + of one battery and the - of the other I dont quite see how its possible to charge one more than the other?

Thanks
 

ifixit

Joined Nov 20, 2008
650
When you buy 2 batteries off the shelf they will not be closely matched with respect to internal impedance. I.E. they may not take a charge at exactly the same rate. This usually is not a problem if charged at a slow rate like C/10, but if you want to fast charge them at 1C then there could be a problem. I'm sure you want a reliable charging solution that will last for years.

Inside a 12 or 24 volt battery all the 2 volt cells are match to each other by the manufacture to ensure they charge and discharge at the same rate. However, don't charge them faster than the manufacturers recomended rate. If you need a fast charge battery then be sure it is specified for that rate. They usually cost more.

The least expensive solution is likely two 12V SLAs charged from one 24V charger at C/10. Would that work for you?

Regards,
Ifixit
 

Thread Starter

bowlingo

Joined Jun 29, 2011
162
The least expensive solution is likely two 12V SLAs charged from one 24V charger at C/10. Would that work for you?

I am very sure this would be fine does this mean if i am using 2 x 12V 4AH batteries in series C/10 is a 10th of 4AH so a 400mA charge i.e a YCP03A24 300mA 24v charger...


http://www.google.co.uk/search?hl=en&q=YCP03A24&meta=#q=YCP03A24&hl=en&prmd=imvns&source=lnms&tbm=shop&ei=U4gbT5TnBpaosgbO_q1H&sa=X&oi=mode_link&ct=mode&cd=6&ved=0CBIQ_AUoBQ&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=ce2122b9af33b928&biw=1280&bih=693

I am looking to use two of these

http://www.ebay.co.uk/itm/Yuasa-NP4-12-Battery-/120821861637?pt=UK_ConsumerElectronics_Batteries_SM&hash=item1c218b4d05

The trouble is it looks like the charger will only do two of the NP2.3-12 (2.3AH/12V) I am looking to charge the next 3 sizes up
 
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