11 Fixed Voltage Settings For a 130 Ampere Charger

BFL13 wrote:
BTW, Some folks want a voltage sensing wire to get the battery voltage showing at the charger.

But that voltage drop gets smaller as current tapers, so by the time the battery is nearly full, there is hardly any voltage drop. So who cares about this magic sensing wire? It doesn't help you with anything I can figure out.

The idea is to have whatever voltage the charger is set for actually show up on the battery(ies) terminals - regardless of wire size - from the beginning right on through until the charger (automatically), or the operator (manually), changes the output voltage setting of the charger.

This extra sensing wire makes up part of a feedback loop that enables the charger's circuitry to at all times compensate for voltage losses in the cabling between the charger and the battery(ies). (Basic EE feedback loop principles.)

What you get is battery terminal voltage during charging stages exactly what you want it to be - and maybe exactly what voltages the battery manufacturer specifies to be held on the terminals during the Boost, Bulk, and Float stages.

A charger that - can force exact voltages onto battery terminals, adjust this voltage in accordance with the air temperature around the battery, and power factor correct for the incoming AC power to the charger would be "ideal", IMHO. Whether any of us could afford a charger like that might be an issue. :)

Mex seems to be getting closer and closer to this ideal with his excellent component searching. What may be taking so long is he probably is trying to arrive at this ideal in a way that we mortals can afford.

P.S. In my previous life we used $300K-$400K automatic testers that could present whatever voltage onto the leads, at whatever current flow that could be accepted into the leads - of integrated circuits we were testing. But the $$$$ four-quadrant power supplies in those testers did indeed border on "magic".

With 11 voltage settings the charger should easily be able to match the battery specifications.
However I am sticking with my automatic charger ;)

"The idea is to have whatever voltage the charger is set for actually show up on the battery(ies) terminals - regardless of wire size - from the beginning right on through until the charger (automatically), or the operator (manually), changes the output voltage setting of the charger"

Phil, I cannot see the value in that, because the battery voltage at the start is say 12.2v and you set your charger to 14.8v and connect up. The resulting voltage on the connecting wires is somewhere between 14.8 and 12.2. It will kick off at say 13.7 and rise from there. It is not going to be 14.8 until the battery is charged.

What difference can it make to anything if there is some voltage drop along the wires? It does matter for telling a solar controller when to start controlling. In that case you want the controller to know the battery voltage is actually at the controller's high set point so it does not stop charging too soon.

But with a normal charger, the battery voltage continues to rise all the way through the absorption stage, so who cares what voltage it gets to before that starts?

That end of bulk voltage has to do with the charging amps wrt battery bank size. It does not occur at the charger's set voltage which is still at 14.8, but at the voltage existing between 14.8 and whatever the battery is up to by then. Might be 14.3, eg.

What can the sensing wire do? It cannot change anybody's voltage. The battery voltage is from the chemical goings on inside it. The charger's amps are set by its own current limit for Bulk, and then by the battery acceptance for Absorption. The sensing wire can't change the charging amps. So what good is it doing anybody?

Well, here's what happened when a good old Parallax 7345 single stage converter can do, charging-wise, when it's 13.6-13.8 volt output voltage is forced to actually be present on the battery terminals via the 7345's output feedback loop sense point being moved right to the battery terminals.

Read Salvo's 12/21/10 07:32pm post in this thread:

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/24657912/gotomsg/24658238.cfm#24658238

Phil, thanks. I note Salvo never did answer my question. :)

He seems to say he got better results by jacking the voltage up from 13.8 to 14.3? so of course it did better. I am not sure this is the same thing as a sensing wire per discussion.

AFAIK a sensing wire just senses (sends?) what the voltage is at one end of the wire to the other end of the wire, but can't change what is really going on. Wrong?

I think "Wrong?" if Salvo did what I think he did to his 7345.

Many power supplies have their output voltage controlled via a closed "feedback loop", with a sensing point for this loop near the output point (the output terminals) of the power supply. Without getting too deeply into how circuits work, what this does is to keep the voltage on the output terminals where it belongs (or where it was set at).

For a charger, moving this sensing point out to the battery terminals then makes the circuitry "think" that the battery terminals are now the "output point" of the power supply. The circuitry then internally adjusts the power supply's output voltage to whatever it has to be so as to get the sensing point (the battery terminals) to be at the voltage that was set on the power supply.

Volt drop compensation is used in long wire circuits. 10' of 2 AWG is being used in this circuit. The clamps are high spring tension copper and the jaw contacts have a shut. The highest voltage drop I can imagine is fourth column -2 max.

Having a timer precludes use of remote sensing. The unit would compensate with 16.45 volts and when the relay contacts close there would be drama.

I still don't get why moving the voltage point to the battery terminals does any good. The charger is at its max amps, so raising the voltage doesn't do anything during Bulk.

In Absorption, the battery acceptance controls amps in. However it is true that a higher battery voltage at any given SOC will make for a higher amp acceptance, speeding up the recharge somewhat.

The thing there is how much good is that? Amps are tapering and reducing voltage drop from that, making the sensing wire less valuable the higher the SOC gets.

Have to see a test run side by side to see if Brand X really is such a loser.

Remote sensing is ONLY USEFUL in badly executed circuits where power leads are too small, voltage drop is too high and they want to slap a band-aid on the voltage drop.

Voltage sensing can allow cheating on voltage set points. Lower the sensed voltage point and raise the output voltage.

Solar systems like the one I built 20 years ago that have say a 230 feet distance between the panels+controller to the batteries can benefit from remote sensing. 460 feet is a lot of wire.

But for automotive and especially a battery charger, voltage compensation is the badge the hallmark of design error...

Batteries usually specify a charge and float Voltage. Charge is perceived as synonymous with the chargers Absorption stage.

Without Battery Voltage Sensing(BVS), you guarantee that the charger's Absorption stage will begin at a lower Voltage and the battery will only reach its specified Absorption Voltage at the end of the absorption stage.

Doesn't Absorption mean that the Voltage at the battery terminals is equal to the battery's charge spec? Likewise for float?

HTH;
John