Battery Charger Load

Well the first problem is the clarity of what you are trying to do? Are you trying to use a battery charger as a DC power source for a fixed DC load or are you trying to bypass a substation protection relay? Depending on the type of battery charger being used, one can easily use one to power some DC loads without modification of the charger. Now nearly all substation protection relays operate on an AC signal instead of a DC signal that all battery chargers produce. These relays also respond to anticipated fault conditions that a substation can experience. These responses protect the substation from a cataclysmic event from damaging the substation. If the relay gets signals from a battery charger instead of the appropriate sub station signals, the protection has been defeated.

I think that you are trying to sabotage a substation with our assistance. This is why you're trying to ask this question anonymously. Go away, fool.

what i am trying to say is that i wanted to use the battery charger as a DC power source for a fixed DC load. i am trying to look forward on what problems will arise for this kind of set up? it is for sure that this power source will be out in cases of power outage.. the battery charger that i am speaking of is the kind of which doesn't have a float. it is basically a local battery charger on which you need to turn it off manually when the battery had been fully charged.

some advices please.. im not trying to sabotage this one.

That does not explain cogently what you are trying to do. You need qualified technical help, or at least a good translator.

It depends. If you are relying on DC to provide some protective functions in case of AC power loss, the charger will also lose power and will not do the job. Doh!

You can buy dedicated substation battery chargers that will supply a base load as well as charging the batteries. The batteries only come in to play on mains failure. Provision is included for mains failure alarm. I've fitted several made by Cloride.

yes sir i understand that buying a suitable station battery charger is better than thinking of other ways. but what i am trying to ask is that what will happen to the relays, the trip coil and other devices which requires DC power source if an ordinary battery charger will supply them? and on the other side, what will happen to the battery charger? is this possible? regardless of the fact that if the power source will be out, the battery charger will also be out.

Yes but want you want is DC power pack. Don't know it's a good thing on a substation. You loose power you loose control functions. That's why it's ran on batteries.

How much amp output from your charger? How much amp your equipment need?

How long, what voltage do you need after the power goes off? Seconds, minutes, hours? Relays, motors, lights? I'm thinking ultra capacitor here, or AGM battery.

Another point in line with RAMConsult's notes on cheapo battery chargers- usually the rectifier is a half bridge, resulting in some significant ripple at twice the line voltage...

additionally the relay contacts may be driving a switch with a motor load that draws significant current. A battery, especially a larger battery has very low source impedance and may supply very large currents to start and run winding motors. Such a DC supply would not likely supply the required current.As many others have suggested it is just a BAD IDEA.

---->Many el-cheapo battery chargers are simply a transformer followed by a rectifier. What that means is that there is no filtering and no regulation, the output will vary according to the nature of the load, especially if it is not directly across a large enough battery.

thank you sir. that is what i want to know. but we have this instance wherein the batteries were out of service for some time and have replaced the DC power source from batteries to the station battery charger. the protective relays had its power source directly from the station battery charger. all i wanted to know is that will the ordinary battery charger will not send off too much current to the relays? will the battery charger only send current to the relays and other loads with the specific amount of current the the relays need?

Hai !

Protection relays(indications) required backup power when the main power fails also.If battery replaced with the charger, when main power fail charger alone cannot give DC power and entire system fails so battery back up is very essential for sub-stations.

NO: Do not substitute Charger supply to power "Safety/ Protection" relays as they are designed to work on Battery.

YES: You can use a battery charger as DC power source; may be some minor modifications require.

<< what i mean is to make the battery as the direct source of power for some protection components of a substation such as the protective relay, the tripping coil of the circuit breaker and etc in replacement of the battery in the substation. what will be the problem if this is the case? >>

Have you not mixed up your question in 2nd para.

But I reply as the other members has understood.

1. Mind it that that all devices in power distribution / control if operated with Battery Power then you never try unless you fully understand Why?

What when power fails or brown-outs?

2. As mentioned by so many members 'NO' I second it unless you modify it with adding DC filter [Try to understand the difference between a Charger and an Adapter]

I would not recommend in doing this as many lead acid battery chargers (we are talking about LA Battery chargers I assume!), when unloaded, provide a far higher voltage than a nominal 12 volt battery. This could damage delicate equipment. It could get to over 17 volts, depending upon the design.

Voltage regulation is usually non-existent as well....

But a charger can be a cheap source of a good metal box, a current meter and a transformer, far cheaper than you can buy them separately. So its not a bad place to start.....

Not knowing how many amps you need makes answering your question for a power supply difficult to answer, but if 5 or 10 amps is enough, look at LT1074 chips (use two for 10 amps). They are DC step down regulators, very efficient and as safe as when building yourself.

Don't forget that the mains voltage part can be dangerous in the wrong hands.....

Best of luck.

There is one most important point that is missing from the replies I see till now.

When a short circuit occurs near to the substation the voltage at the substation will collapse, thus the input voltage to the charger will collapse (if the charger supply is from the substation). This will mean no output DC to power the trip coils of the circuit breakers and for the protection relays (if electronic). Result; the circuit breaker on the faulty circuit will not operate, the fault will not be cleared as intended, and most likely extensive damage will be done to the equipment carrying the fault current, and there is high risk of injury or death to persons in the vicinity of the fault.

The battery in protection schemes is acting as a UPS, and is there to ensure that the protection scheme will work at all times.