Problem In Substation Battery Charger 125DC /30A

You need to check the charger circuit. Seems soem are by-passed/ not working. Check the circuit thouroughkly. If it is giving 2oov as agisnt 220 V no wonder that that the battries are not getting charged.

You say you have a charger problem, but you could actually have a battery problem. You have 10 batteries, nominal 12 volts, (assuming lead acid) normally would sit at 13.2 volts per cell, ie 132 volts, and float a bit higher, depending on the battery type. However these are working batteries, whilst you have given no figures on the load the coil, etc. would draw, it may be large, or, during a blackout, (which is presumably why there are batteries needed) the batteries may be heavily discharged, so will need a higher voltage to recharge, up to 2.5 volts per cell, so 150 volts required by the charger, and as chargers have to have a higher voltage for current to flow, the charger will actually be putting out more than that, particularly if it is open circuit, (as you said the batteries are damaged.) - it is not inconceivable the voltage open circuit could be as high as 200 volts particularly if it was made for 220 volt operation so the voltage is a tad higher. This would not normally be a problem, the charger itself would be controlling the output voltage to the batteries, depending on what charging algorithm it has, - so if the voltage you measured was open circuit there is no cause for alarm. However there is a question to my mind on the battery size, - your charger claims to put out 30 amps, normally batteries can only be safely charged at 10% of their capacity at C10, so that would imply the battery bank would need to be 300 Amps @C10, - 300 amps is very big for a 12 volt battery, normally that size would be 6 volt or even 2 volt units connected in series, (actually there is no such thing as a 12 volt battery, it is just salesman spruik, lead acid batteries are made up of 2 volt cells, whether stuck together or not, connected up in series, the number of cells giving the total battery voltage) and also normally a 300 amp "12 volt battery" is hard to get with the characteristics for long term float/cycle use such as your situation describes. I would suspect that the original batteries, when they failed, were replaced by smaller amperage batteries, - to save money or because they were too heavy or whatever, so now they have had far too much current for too long and have been severely damaged. If you check out my assumptions and find they are correct I would suggest you replace those batteries with 2 volt cells of at least 300 ampere hours capacity @C10, preferably Tubular Positive, which are now available with a design life of 22 years, and unless the charger has been designed for sealed batteries use flooded, with re-combination caps to reduce water use. - That is assuming they are in a proper battery enclosure with appropriate ventilation, - with flooded, not only will they last longer but if the charger is putting in too much you will have warning because of excessive water use and harm will normally be limited to high water use. If that happens, you may need to replace/re-calibrate the charger. Cheers, Geoff Thomas.

Correction, I said in line 2-3, 13.2 volts per cell, should have been per "battery" Geoff.

thank you sir for your reply to my query. but then again, your comments made me more confused. i am certain that the problem is in the battery charger. there aren't any problems in the batteries since these equipments were operating just fine just before the battery charger failed. what i am asking is that what would have cause the battery to fail considering that in the normal charging operation of the charger, the charger would have an output voltage of 125vdc based on its plate and i have confirmed this through measurement. in went off to 200vdc just this month and i wasn't able to figure out what went wrong on the circuitry of the charger.

sir, i am certain that there isn't any problem on the load, e.g coil, protection relay.

hoping for another idea from you.

Dear Prometu, I suspect you need to much more carefully read my letter, - I took quite a time to write it for you but you are just repeating your self again without checking the points I raised. Of course if you have been told by God that it is the battery charger I would have to defer to higher authority, but would God support your not reading the letter? Cheers, Geoff. PS if you need me to clarify any point please ask. G.

Hello Prometu,

First of all, if you have a 10 12 VDC batteries, it means you have a "120" V system. In reallity, you need to keep your batteries in "floating" operation, which means around 13,8 VDC per battery (assuming they are lead acid batteries). This means you need a voltage of around 138 VDC to keep them charged. If you had this over voltage of 200 VDC over the system, than for sure the cells wont work anymore. Tell us, what is the brand of the battery charger? what options do you have in the front pannel? can you use software to set parameters for charging the batteries? What type of batteries do you have there? Chances are, your charger was set incorrectly. Let us know, so we can help further.

There is DEFINITELY a problem in the battery charger. Control circuit which regulates the output voltage to within permissible limit, has failed AND/OR output voltage adjust potentiometer is open. There should be a "charger fail" or "output voltage high" alarm going on. Pls. confirm if this alarm is available or not. Pls. check the voltage adjust potentiometer, if it is there.

We manufacture battery chargers for power plants & substations and hence I am sure about this.

Hi Ashok, I submit we need more information, on whether the voltage he reported was open circuit, what was the damage to the batteries, what is the size of the batteries, @C10, also the type, - whether flooded or sealed, and also more info on the charger, as you request. Selling battery chargers doesn't mean you know, there are some bad battery chargers out there, but also wrongly designed systems and in-appropriate batteries, which is why I always suggest suspending judgement until all the facts are in. We now await Prometu providing his information. Cheers, Geoff.

Dear Lookfar

Thanks for your posting. I will clarify few points mentioned in your posting.

First & foremost, I donot intend to criticise, directly or indirectly, any company in any field, including competitors ( you wrote, there are some bad battery chargers out there ). Failure of equipment is possible, including those supplied by us, for various reasons.

Second, my posting was based on the "symptoms" mentioned by Prometu.

Third, 200 V open circuit voltage is very high EVEN for Flooded or tubular lead acid battery which has max. boost charging voltage of 2.75 V/cell. Thus for 125 V system with 62 cells, max boost charging voltage is 170.5 V. Prometu mentions 200 V DC.

Last but not the least, I donot intend to promote our products on this forum, which I consider is a forum to share technical problems and querries. My statement of being a manufacturer was only to inform about first hand experience in the equipment under discussion.

Rest is fine, Good wishes, Cheers and enjoy, stay fully charged!!! ( we are talking of battery!!! )

Ashok Toshniwal