Converter/Charger Voltage vs. Battery Voltage

[wfred]

I recently upgraded my converter/charger and read 14.8 volts in the lugs of the converter charger when it is in boost mode. I also read 14.8 volts at the ring terminals for the batteries with the batteries disconnected. If I connect the ring terminals to the batteries, I read 13.6 volts.

Is this voltage drop normal or does this indicate a battery issue?

[tenbear]

What size wire is used to connect the converter to the battery? The original wire in mine was AWG #8. When I replaced my Parallax 7345 with a PD 9260 I replaced the #8 wire with #4, much fatter, less resistance, higher voltage at the battery when charging, faster charging.

[SteveAE]

Fred,

You can easily verify for yourself that there indeed is voltage drop in your wires.

With the battery(s) connected, the charger turned on, and your voltmeter set to DC Volts, do the following:
Put the positive (red) lead of your voltmeter right on the output of the converter and put your negative (black) lead on the positive terminal of the battery (you can use small gauge wire to extend your test leads if necessary). The voltage you read is the drop in the positive line to the battery. Assuming the same size wires and condition of connectors in the negative lead, the drop there will be about the same. So total drop will be about twice what your voltmeter reads.

Most of us have fought this battle at one time or another, so welcome to the club.

Steve

[BFL13]

wfred wrote:
I am not sure of the SOC of my batteries, since the converter didn't drop to storage mode, I assume they are charging

I don't have voltage loss from my wires. I remove the ring terminal from my batteries and use my multimeter to check voltage at the ring terminals and it reads 14.8 volts. When I connect the ring terminals to the batteries, I use the same multimeter to check voltage at the same ring terminals. The only difference is that now they are bolted to the battery terminals. The voltage reads 13.6. The voltage only drops when the wires from the converter are connected to the batteries. I am not sure if this is because the batteries aren't at 100% charge or if it indicates sulfur on the plates or some other problem.

Thanks for the help,

Fred

This does not indicate anything wrong with the batteries.

The "only difference" is not so much that they are now connected, as that now when connected the wire has current flowing in it, and now you see the voltage drop. No current, no voltage drop.

The amount of voltage drop is related to the resistance of the wires (pos and neg together total) and the amount of current. More current more voltage drop on the same wires.

So everything is normal, except you have a larger voltage drop than you should for that much current, indicating too much wire resistance. No problem on shore power- it will still work ok, but if you want faster charging, less generator time when off grid, you should :
-rewire with fatter wire
-move the converter closer to the battery bank (so shorter wire)
-move converter and use shorter AND fatter wire.

[time2roll]

If you expect fast charging then 1.2 volt drop is on the high side.
Yes the wire is too thin, too long, or there are some poor connections. Or some of all these.

Could be even worse than you think as the converter is voltage limited in your test.

[Snowman9000]

The volts drop while the batteries are accepting a lot of current. As the cycle continues, you should eventually see 14-something when the current starts to taper off.

[Mandalay_Parr]

Batteries probably not charged. Wait 24 hours with charger on and check again.

[wfred]

I am not sure of the SOC of my batteries, since the converter didn't drop to storage mode, I assume they are charging

I don't have voltage loss from my wires. I remove the ring terminal from my batteries and use my multimeter to check voltage at the ring terminals and it reads 14.8 volts. When I connect the ring terminals to the batteries, I use the same multimeter to check voltage at the same ring terminals. The only difference is that now they are bolted to the battery terminals. The voltage reads 13.6. The voltage only drops when the wires from the converter are connected to the batteries. I am not sure if this is because the batteries aren't at 100% charge or if it indicates sulfur on the plates or some other problem.

Thanks for the help,

Fred

[mena661]

wolfe10 wrote:
Are the batteries fully charged when you read this voltage difference?

If not, it is likely line loss (resistance in wires from charger to batteries). The more the amps you are pushing to the batteries, the more the line voltage drop from resistance in the wires and connections.

X2

[wolfe10]

Are the batteries fully charged when you read this voltage difference?

If not, it is likely line loss (resistance in wires from charger to batteries). The more the amps you are pushing to the batteries, the more the line voltage drop from resistance in the wires and connections.