Help with voltage drop

[brianmay27]

Hello all. At my job, we have a problem. Our APC batteries are bad and would cost 250 for new ones. But we have a "battery backup" the past compiney left us with 8 car batteries. thay have it so it is 58 volts and so is the charger. We were going to just make the batteries 12 volts and the max AH. and get a very good inverter. But that would require us to reduce the voltage from 58V to about 14V with a max of 12 amps possibly going through. Does some one know of a cheep way of doing this?

[Externet]

You will have to phrase your explanation properly. And we do not need to guess whatever your APC means.

Make it clear and will be able to help.

Miguel

[brianmay27]

ok i will try to help as much as possible. I will make it a before and after so what we have now and what we want after doing what ever. Before: a large battery charger. (input 112V output now 58V at 12 amps max.) there are 8 deep cycle (gel) batteries linked to make 58V and 160 AH (each battery is about 14V EQ and 13V float and each have 80 AH) This was used as a backup for a phone system that used DC so no need to convert it. But the phone sys is broken and we want to use the batteries as a backup source. So we want to get a 12V DV to 110V AC inverter. After: 8 batteries linked up so 14V total with 640 AH and have a 12V DC to ac inverter attached. running continusly.

 

The problem. Need some way to bring down the power from the charger from 58V to 14VDC so it can charge the batteries. BUT 12 amps MAY be going from the charger to the inverter. So resisters are probly out of the picture. So just if this is needed. we will be using at least 10A from the inverter to our computers.

 

Hows this?

[Spyman]

First I need to point out that 58V x 160 Ah is 9kWh and 12V x 640 Ah is only 7.7 kWh. You are not going to get more duration out of the new configuration. Whitout the mains supply and with a load of 1.1kW the batteries will only last for 7 hours max, I would guess 5 hours.

 

Second, if the converter uses more than the charger can support the batteries will eventually drain, even with the mains supply. The converter will at least use 12 VDC 92 A to support 110 VAC 10 A.

 

Third, the charger can probably be rebuilt to an output of 12 V but not likely to 92 A, I would guess more than 100 A is needed if to be running continusly.

 

You are going to need a new charger to be running continusly.

 

Even with a different converter for 58 VDC to 110 VAC you will start to drain the batteries with a load of around 5-6 Amps with the old charger.

 

What you need is a converter with a bypass system so it will only use power from the batteries when the mains supply is off, then a good car battery charger should be enough to recharge and keep the batteries fit for fight. (Or a converter with bypass for 58 VDC to 110 VAC and keep the old charger.)

 

Link about UPS: http://en.wikipedia.org/wiki/Uninterruptible_power_supply

[Rocket Man]

for a bypass, you could use a normally closed relay in parralel with the charger to control the output to the circuit. (when the mains are on, the relay removes the batteries from the circuit)

 

if you use a common ground, the normally open portion can link the charger to the batteries when there's voltage on the mains.

 

you should probably put all the batteries in parrallel, then they can run at optimum voltage or close to it. a 12V charger shouldn't be too expensive.

[Externet]

Hi.

The battery bank of around 58 V has a 12 Ampere capable charger but that does NOT mean it's meant to work at its full rate; probably less than half that, and after a mains failure.

The 80 Amperes hour battery bank can supply telephones for a small town.

The 12 V backup power you want to use cannot be for a telephone system. Telephones work with ~50 Volts.

 

Then, I assume the backup system you want to implement is to supply 115VAC for computers or whatever else but not telephony.

Those 640 Amperes hour in 8 batteries paralleled to 12 Volts are to supply how many watts of 115VAC? That is neccessary to know.

 

If your answer is say, 240 Watts You need an inverter capable of around 500 Watts continuos duty.

 

The battery charger has to be an 12V automotive type. Its Amperage capability is to be calculated by the time you expect to need to charge the batteries after a power failure.

 

Modyfying the existing 58V charger would need to parallel secondaries of the transformer (if there are taps on it, which I doubt) and add rectification and regulation capability (major surgery)

 

In other words, you may not be able to use the telephony charger, and you have to buy an inverter capable of supplying the computers power needs and powered by 12V if you insist in paralleling them.

 

---->Look for a continuos duty inverter (or UPS) that uses FOUR 12V batteries in series for nominal 48 V DC input AND capable of supplying the power demands of your computers and then you are done, reusing the same telephony charger.

 

Thinking on using a 12V input inverter is shortsighted, I do not think they exist for large powered outputs.

 

Find a 48V input inverter and you can use the existing charger and batteries, BUT in series. And do not exceed 56 Volts during charge. If it is not an inverter but a UPS, it will have a charger circuit built-in anyway.

 

Miguel

[Spyman]

Thinking on using a 12V input inverter is shortsighted, I do not think they exist for large powered outputs.

I would also go for higher battery voltage, but there exist solutions for large power outputs from 12V.

 

Here is one with 12.5 kW of output power: http://www.victronenergy.com/upload/documents/PIN012601000-D-cUS.pdf