dc voltage generator

[hankthegonk62]

i would like to build an ac supplied variable dc output generator for creating a specific voltage (12 to 82 vdc) to set up battery chargers as used on forklift trucks . i need to be able to get a specific voltage to adjust gassing/equalising to be able to adjust control pot on control card rather than wait for hours for the battery to reach this voltage to be able to set this up . it does not have to have a built in voltage readout as i should be able to monitor this at the control card with a meter . any help or advice would be grately appreciated .

 

[ronv]

That's a biggie. I don't know to much about forklifts but have some experience with golf carts. I think forklifts have really big batteries. How many amp hours? This will limit your maximum charge current. But lets say they are 200 amp hour. That would put your charge current at 20 amps maximum. This would put you on 220 input voltage to your transformer. Do you have some existing transformers?

 

[Diver300]

Do you need the device to produce much power, or is it just simulating a battery being charged?

How much power or current does this device have to produce / absorb? You might be able to get away with something quite simple if the currents aren't too big.

 

[hankthegonk62]

it is only to simulate as you say battery voltage at the control card which needs to be only about 0.5amp to 1 amp and further to my post i neglected to work out that it would need to be around 100vdc output . it basically simulates for example a 48v battery (24 2volt cells) reaching a gassing voltage calculated at 2.35vpc(volts per cell) to allow me to adjust the control card to switch to gassing state by way of a potentiometer at 56.4v . so for a 80v battery the same calculation would apply but just change the number of cells ie. 40 x 2.35 and so on . the main thing it should be adjustable to whatever voltage i need as there are different batteries i need to work with . thanks

 

[hankthegonk62]

this is the reply i posted to someone else maybe it would clear up my misleading you a bit sorry.it is only to simulate as you say battery voltage at the control card which needs to be only about 0.5amp to 1 amp and further to my post i neglected to work out that it would need to be around 100vdc output . it basically simulates for example a 48v battery (24 2volt cells) reaching a gassing voltage calculated at 2.35vpc(volts per cell) to allow me to adjust the control card to switch to gassing state by way of a potentiometer at 56.4v . so for a 80v battery the same calculation would apply but just change the number of cells ie. 40 x 2.35 and so on . the main thing it should be adjustable to whatever voltage i need as there are different batteries i need to work with . thanks

 

[Reloadron]

OK, so all you need is a variable DC source to simulate a battery or batteries. You don't really need any current to speak of. Maybe just consider a Variac with a full wave bridge on the output. Even though 5 Amps is overkill a simple 5 Amp 0 to 140 VAC Variac should work with a bridge hung on the output and fuse the output at about 1 Amp. That may work.

Ron

 

[hankthegonk62]

thanks for that it gives me some idea now . appreciate your help .

 

[Diver300]

You should note that variacs are autotransformers, so they don't isolate. You should have an isolation transformer as well.

You don't say what the mains voltage is, a step-down transformer will usually be an isolation transformer anyhow.

There will have to be a capacitor to keep the ripple down. A battery will have no ripple, and I don't know how much some ripple will affect your circuits. If you are taking 1 amp, you need about 10,000 uF to keep the ripple below 1 V. That will be quite an expensive capacitor.