Charging AGM battery

[Raz]

Originally Posted by Raspy

Means nothing?

A bit of an over simplification there, since voltage is relatively constant and amps are wildly varying both on the charge and discharge side, as well as with different battery capacities and expected loads.

I'll do you one better.

Low voltage DC is not easy to get through wire without losing power due to voltage drop or resistance. It is huge problem in an RV. Use big wires and short wiring runs to get around this. It is good practice to use one or even two sizes bigger wire than recommended to limit voltage drop.

First, voltage is aways across never through.ie a difference of potential.

Next, the voltage drop of a charge line is always the difference between the two batteries and is independent of wire size. The wire determines the current. Basic DC circuits.

[Alex Adams]

Originally Posted by Raz

Next, the voltage drop of a charge line is always the difference between the two batteries and is independent of wire size. The wire determines the current. Basic DC circuits.

So a 20 amp 12 volt current traveling a 10 foot 14 gauge wire would have the same voltage drop as a 20 amp 12 volt current traveling a 10 foot 8 gauge wire? That's not what I see when I calculate the voltage drops for each.

[Raz]

Originally Posted by Alex Adams

So a 20 amp 12 volt current traveling a 10 foot 14 gauge wire would have the same voltage drop as a 20 amp 12 volt current traveling a 10 foot 8 gauge wire? That's not what I see when I calculate the voltage drops for each.

How did you get 20 amps? You can't just make up a current. Cause and effect. Draw the circuit. Two batteries series opposing. A resistor between the positive terminals. A resistor between the negative terminals. It's a simple series loop. The batteries subtract. That's the voltage across the resistors ( charge line ). The charge current is the difference between the two batteries divided by the charge line resistance. Ohms law. A larger wire increases the charge current.

[WDavidG]

I posed my original question about whether the PD converter with charge wizard on shore power or the constant voltage charge from the TV while towing created any problems of over-charging, or otherwise, for an AGM to Lifeline Batteries and just received a response from their tech person. His answer basically - don't worry, neither situation is a problem for their AGM batteries. He did caution that during the off-season care should be taken to properly maintain the battery. The response from a similar question to Trojan Batteries was essentially the same.

This seems to confirm the comment by David Watson from PD that Mike shared earlier in this thread.

So...I'm ready to invest in an AGM and not worry about it. More snow today and another 10" forecast for Wednesday, but ordering a battery will help put my mindset on spring camping.

[Raz]

Originally Posted by WDavidG

I posed my original question about whether the PD converter with charge wizard on shore power or the constant voltage charge from the TV while towing created any problems of over-charging, or otherwise, for an AGM to Lifeline Batteries and just received a response from their tech person. His answer basically - don't worry, neither situation is a problem for their AGM batteries. He did caution that during the off-season care should be taken to properly maintain the battery. The response from a similar question to Trojan Batteries was essentially the same.

This seems to confirm the comment by David Watson from PD that Mike shared earlier in this thread.

So...I'm ready to invest in an AGM and not worry about it. More snow today and another 10" forecast for Wednesday, but ordering a battery will help put my mindset on spring camping.

If you're looking at Lifeline, do shop around. The prices can vary by $100. I bought mine from Inverters R Us. They were the cheapest at the time (2014) Good luck.

[Glenn Baglo]

Originally Posted by Raz

If you're looking at Lifeline, do shop around. The prices can vary by $100. I bought mine from Inverters R Us. They were the cheapest at the time (2014) Good luck.

Must be a real innovative company.
Do they flop the R in their name too?

[Alex Adams]

Originally Posted by Raz

How did you get 20 amps? You can't just make up a current. Cause and effect. Draw the circuit. Two batteries series opposing. A resistor between the positive terminals. A resistor between the negative terminals. It's a simple series loop. The batteries subtract. That's the voltage across the resistors ( charge line ). The charge current is the difference between the two batteries divided by the charge line resistance. Ohms law. A larger wire increases the charge current.

You misunderstood HandyBob's point. It was about the size of the wiring going from the source outputting the charge current to the batteries. If that wire is a small diameter run for a long distance, you will not get enough voltage at the batteries to charge them properly. If your charging source puts out 14.4 volts at 20 amps and the wire going to the battery has a 2 volt drop, you are only charging with 12.4 volts at 20 amps. If, on the other hand you use a gauge of wire whose voltage drop at 20 amps for the same distance is only .2 volts, you get 14.2 volts at 20 amps at the batteries. Which would end up charging the battery fully?

[WDavidG]

Originally Posted by Raz

If you're looking at Lifeline, do shop around. The prices can vary by $100. I bought mine from Inverters R Us. They were the cheapest at the time (2014) Good luck.

Thanks for the tip Raz. I have noticed, and been surprised, at the large price variation. Amazon is on the high end. Best I've found is Battery Guys - best price and free shipping. I wasn't aware of Inverters R Us however - I'll check them out.

[NEWYORKHILLBILLY]

Originally Posted by John in Santa Cruz

I installed a PD4645 in my Casita to replace a failed Parallax. When you put it in AGM mode, it does NOT do the 'equalizing' thing.

John I had another email conversation with Progressive Dynamics today.

They confirmed that it does do a equalizing mode in the agm setting. He also told me there is no way to turn it off.they state it will not Hurt the battery .

[Raspy]

Alex,

Either of your examples will charge the battery fully as long as there are no loads other than simply charging the battery.

The smaller wire will simply mean the charging takes longer, but it doesn't mean it won't charge. Not sure what you mean by "properly".

The "Bulk"phase will take longer, but as the battery moves into it's "absorption" phase the amps are reduced. With reduced amps the voltage will come up to and be held at 14.1 or so. This will bring the battery to full charge. Then the battery will go into "float" and settle to about 13.2.

The problem would be if there was a 30 amp load while trying to charge with the smaller wire. Once the battery is charged, it will carry heavy loads for a while that can then be made up over time after the load is gone. Starting batteries experience this all the time. A starter motor or winch might draw 400 amps, while the alternator is only capable of 100 amps output. The load has a short duration and the charging system makes up for the loss over time.

[Raspy]

Another point about charging with two batteries:

If you have two 12 volt batteries connected in parallel, connect the charging leads with the + on one of the battery's + terminal and the -- on the other battery's -- terminal. This will make them come up to the same level of charge. Connecting the charging leads to only one of the batteries, in a parallel battery arrangement, will result in a lower state of charge in the battery not connected to the charging leads.

[John in Santa Cruz]

wire has a constant resistance per distance. heavier gauge wire, lower resistance, thinner wire higher. longer distance is higher, shorter is lower.

if the power source (charger) is outputting, say, 14.4V, and there's no load across the far ends of an arbitrary wire, you'll get 14.4V, whether that wire is 1 ohm or 0.1 ohm. if there's a 12.4V battery at the other end of the wire, the 1 ohm wire will pass 2V (14.4-12.4) / 1 ohm = 2 amp, while the 0.1 ohm wire will pass 2V / 0.1 = 20 amps.

now, in reality, battery charging is much more complicated than this, because that 12.4V battery also has internal resistance, and its an 'active' load, it changes according to how much juice you put into it.... when you pump current into it, the voltage goes up, etc etc.

[Alex Adams]

Originally Posted by Raspy

Alex,

Either of your examples will charge the battery fully as long as there are no loads other than simply charging the battery.

The smaller wire will simply mean the charging takes longer, but it doesn't mean it won't charge. Not sure what you mean by "properly".

The "Bulk"phase will take longer, but as the battery moves into it's "absorption" phase the amps are reduced. With reduced amps the voltage will come up to and be held at 14.1 or so. This will bring the battery to full charge. Then the battery will go into "float" and settle to about 13.2.

The problem would be if there was a 30 amp load while trying to charge with the smaller wire. Once the battery is charged, it will carry heavy loads for a while that can then be made up over time after the load is gone. Starting batteries experience this all the time. A starter motor or winch might draw 400 amps, while the alternator is only capable of 100 amps output. The load has a short duration and the charging system makes up for the loss over time.

What HandyBob is talking about has to do with charging via solar which, I believe, is what NEWYORKHILLBILLY said was going to be his primary charge method. With solar charging you cannot afford to lose too much to voltage drop since you have a limited amount of power supplied by the sun.

[stevebaz]

Originally Posted by Raz

Early Parkliners came with Optima blue AGMs and a Progressive Dynamics converter neatly stored under one of the benches. In at least one case the batteries off gassed. There is a rather long thread somewhere around here detailing the event. Parkliner has since moved the batteries to the tongue. While no cause was given, I came to the conclusion that the lack of ventilation and the destratification mode may have played a part. As my PD 4045 doesn't seem to have a way to stop that mode, I stopped using it to charge my battery. With AGMs being rather expensive, I'd rather not use a charger that wants to boil an electrolyte that can't be boiled.

Raz,
see post 35 at this link and see if it is what your looking for on the pd4045 using agm battery.

Total Electrical Upgrade - Page 4 - Class B Forums

[Raz]

Originally Posted by Alex Adams

You misunderstood HandyBob's point. It was about the size of the wiring going from the source outputting the charge current to the batteries. If that wire is a small diameter run for a long distance, you will not get enough voltage at the batteries to charge them properly. would end up charging the battery fully?

No misunderstanding on my part. The charge line connects two sources, the tow battery and the trailer battery. Because both ends are sources, they both define the voltage drop. Now, replace the trailer battery with a light bulb and you have a voltage divider situation where some voltage is lost across the line. The difference is that the trailer battery's chemical reaction defines its terminal voltage. No chemical reaction with the light bulb.

Originally Posted by Raspy

The smaller wire will simply mean the charging takes longer, but it doesn't mean it won't charge. Not sure what you mean by "properly".

.

Correct. The size of the wire sets the charging current and thus the charging time.

Originally Posted by Alex Adams

What HandyBob is talking about has to do with charging via solar which, I believe, is what NEWYORKHILLBILLY said was going to be his primary charge method. With solar charging you cannot afford to lose too much to voltage drop since you have a limited amount of power supplied by the sun.

No, Bob says "If you cannot get your batteries up to 14.4 volts (14.8 is better & faster) with whatever charging system you have]"

But, with solar you do have a different scenario. If your panel is feeding a charge controller then voltage drop is a consideration. The input of the controller is not a source.


Alex, I've given you the technical arguments and have nothing more to add. Believe what you wish. We spend alot of time camping in the NH white mountains. If you see a bright white Trillium with orange decals pulled by a white Frontier, do stop in. Raz

[Raz]

Originally Posted by stevebaz

Raz,
see post 35 at this link and see if it is what your looking for on the pd4045 using agm battery.

Total Electrical Upgrade - Page 4 - Class B Forums

Thanks for the heads up. Nothing in the manual but mine may be an earlier version.

[CalCop]

Wow lots of tech info
But question was, will the parallax charge or harm an AGM battery?