I am trying to get a man lift JLG T350 to work with not so good batteries. I has four 6 volts batteries giving a nominal 24 volts. I don't want it to charge the batteries, but just keep them from reaching the "Low Voltage" fault.

I have this huge Toroidal Transformer: Input 220V, output 0-20 / 0-20 volts, with 2.75 mm secondary copper wires that I connected in parallel (double the current). I added 5 turns of wire which gave me extra 4.16V, and my mains are 240V totaling around 26.5 volts. I added a full wave bridge rectifier using 4 Eupec power blocks DD104N16k 104 amps using the outside connectors, leaving the center pin (Thyristor tab) disconnected. (outside connectors are just diodes) which outputted 26V.

The weird thing that does not make sense at all, is when I connected the Negative clamp to the battery, the output voltage raised to 40V (just the negative!). The Lift is in the yard with the outriggers on the ground, so I thought maybe it was a feedback from ground to the non grounded transformer, but the primary is isolated from the secondary...

I also thought maybe it was just EMI voltage. However when I connected the positive clamp, the current raised to 40A and it dropped slowly to 12A as the voltage reached 30V (way above the supposed 26V), so no EMI here. If I new the voltage would increase, I would not added copper wire I would left it at 20V paralleled... Are Toroidal Transformers suppose to act weird? I retracted then lowered the outriggers all the way and them the ground: The voltage dropped to 22V and amperage increased to 60A, the diodes barely warmed up!!!

-Does anybody have any idea of why the Voltage is Increasing?
Thanks in advance!

 

You seem to be ignoring the fact that the peak voltage of 26.5 volts RMS is 26.5 x √2 = 26.5 x 1.414 = 37.47 volts. When this is connected to the batteries it will try to charge them to the peak voltage. Without a schematic of EXACTLY how your diodes are connected AND what point if any on your circuit is earthed and any earth connection to the batteries I cannot explain why the voltage output from the rectifier rose from (An unspecified value.) to 40 volts when just the negative output was connected to the batteries.

Les.

 

It could be how You are using your Meter,
but without an accurate Schematic it's all just speculation.
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Thanks for the quick answer guys! Attached is a rough representation of the circuit.

I think I figured out the "phantom" 40V when a single clamp was connected to the battery terminal: A rod on the ground would do similar, also when I touched the clamp the voltage would rise a little too. You're right, the circuit is not earthed...

But I am still having a hard time trying to understand the RMS and Peak deal... Everytime I connected a charger to a battery before, its voltage dropped and the battery's increased a little, I've never seen both voltages increase, except this time...

1 - Is it possible that the impure DC (no capacitor) ripples of sine wave valleys is adding to the (+), the crests to the (-) and a digital meter then reads the peak voltage?

2 - If I install a capacitor, would the voltage rise to peak?

Thanks again,
Luiz

 

One issue with modern electronic meters over the old moving coil versions is they can measure spurious voltages, e.g. from an isolated secondary etc, you can often get a reading to earth ground, place a low resistance in this path and the voltage often will disappear.

 

What is "D-6" ?
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Thanks for the quick answer guys! Attached is a rough representation of the circuit.

I think I figured out the "phantom" 40V when a single clamp was connected to the battery terminal: A rod on the ground would do similar, also when I touched the clamp the voltage would rise a little too. You're right, the circuit is not earthed...

But I am still having a hard time trying to understand the RMS and Peak deal... Everytime I connected a charger to a battery before, its voltage dropped and the battery's increased a little, I've never seen both voltages increase, except this time...

1 - Is it possible that the impure DC (no capacitor) ripples of sine wave valleys is adding to the (+), the crests to the (-) and a digital meter then reads the peak voltage?

2 - If I install a capacitor, would the voltage rise to peak?

Thanks again,
Luiz

Sorry, but your schematic is all messed up without any idea of Polarities. All you will get in this is a lot of smoke.

 

D6 is rough representation of the DC Motor Controller which hasn't been a problem so far... I have an old version of EWB that has some funny symbols like AC Source with (+) and (-) on it.

 

I agree! I ran thru that a while back where this company had a cabinet with a transformer PS for the PLCs etc, but it didn't have common ground. You would get 70VAC between cabinet and (-) negative. But when I touched both leads of the meter, the voltage dropped to 10-12VAC. It was difficult to troubleshoot in the beginning until I caught the non common ground. Perhaps they should have a 100 ohm drop down resistor... don't know...

 

What is "D-6" ?

D6 is rough representation of the DC Motor Controller which hasn't been a problem so far... I have an old version of EWB that has some funny symbols (supposed to be an SCR and I could not edit "D6")

 

One issue with modern electronic meters over the old moving coil versions is they can measure spurious voltages, e.g. from an isolated secondary etc, you can often get a reading to earth ground, place a low resistance in this path and the voltage often will disappear.

You're right! I ran thru that a while back where a company had a cabinet with a transformer PS for the PLCs etc, but it didn't have common ground. You would get 70VAC between cabinet and (-) negative. But when I touched both leads of the meter, the voltage dropped to 10-12VAC. It was difficult to troubleshoot in the beginning until I caught the non common ground. Perhaps they should have a 100 ohm drop down resistor... don't know...