General wiring misunderstanding on Nash22H

[pickjare]

Hi, I have a 2001 Nash 22h that is new to us. I just modified battery brackets to accept 2 new Trojan 6V T105 batteries. At same time I installed a Pico master disconnect switch rated for 300A continuous with the intention of using switch to disconnect batteries between trips. And at same time I installed the Charge Wizard for the Progressive Dynamics 9140A factory equipped converter. I spent all winter researching these topics, especially from this forum thank you, and thought I new what I was doing. After all the above was complete, I simulated 2 nights of camping by camping in my driveway and measured current draw from furnace (6 amps), lights, etc., and drained batteries down to 65% SOC (12.33V) as measured with a volt meter after 24 hrs at rest with disconnect switch turned to off to see if we can boondocks 2 relatively cold nights. Alright, next I turned the disconnect on and plugged in the trailer to try out the new Charge Wizard. Here's the strange part: at converter positive is red, negative is white--right? Disconnect switch is installed on negative Cable near converter--I thought that would be a nice place for the switch and assumed those cables went straight to battery anyway so why not. With switch on I measured voltage at converter terminals, 14.4 V and with clamp on amp meter, 21 Amps. I went to negative cable at battery terminal and have only 13.7V but still have exactly 21 amps right at battery. Puzzling. I thought I had too much voltage drop Somewhere and was afraid batteries will be undercharged and as I investigated further I found the cables do not appear to run from battery to converter, instead they go to a power panel. So what have I done by installing switch right at converter negative cable? Is that ok? Same as if it were at battery cable right at battery? As I pondered this, I realized the polarity of charging current was backwards. I am using a quality clamp on meter that shows direction to negative battery terminal and at the converter the negative cable shows current moving toward the converter. This is backwards in my mind as the converters job is to charge batteries. Now I'm real confused. I haven't turned on a single light or anything since I plugged in, and I'm leaving it plugged in for now because converter should have blown fuse if polarity is in fact wrong. Must be my way of thinking. Have I explained this ok? Does anyone know what I am seeing here? Thanks.

[pickjare]

DrewE wrote:

pickjare wrote:
For my voltage drop concern: The converter went into normal mode this morning only pushing about 2 amps and 13.7 volts. The voltage and amperage was exactly the same at battery terminals as at converter connection. Strange how when charging at 21 Amps my amp measurement was exactly the same at the battery terminal as at converter connection, yet voltage was .7V lower. There has to be some electrical law that says no, if voltage is lost in a circuit somewhere, so will current, therefore current flow should have been lower. Ill have to try this again. I am going to assume for now that the .7 volt drop I saw when charging at 21 Amps is because its a long cable, perhaps it should have been made with larger gage.

But, I will continue checking connections and have plans to eliminate crimp on butt connectors. The connections I made use solder on type copper lugs. I did check voltage drop across the switch and through my 6 V battery connector cable, and the cable had 7 MV and the switch had 26MV--wouldn't both be considered acceptable? Connector cable being the 2 foot cable I made to connect 6V batteries in series. I have not done voltage drop across the entire positive and negative circuits from batteries to converter, just checked those 2 things since it is so easy.

There are a few basic electrical laws that come into play here. The first is Ohm's law, which defines the relationship between voltage and current in purely resistive circuit elements (such as wires). It states that E = I x R, where E is the voltage ("electromotive force"), I is the current, and R is the resistance. Since the resistance here is constant, the voltage drop when 2A is flowing is one-tenth that when 20A is flowing.

The second basic electrical law is Kirchhoff's current law. This states that at any junction in a circuit, the signed sum of all the currents is zero--or, put another way, the current flowing into any junction is equal to the current flowing out. Current doesn't pile up. If your circuit is a simple loop, this implies that the current is the same throughout the circuit, no matter where it's measured, as the current doesn't have any differing routes to flow through.

The third basic electrical law is Kirchhoff's voltage law. This states that, for any closed loop in a circuit, the signed sum of all the voltages around the loop is zero. If the converter is supplying 14.4 volts, then the voltage at the battery plus the voltage drop on the positive leg plus the voltage drop on the negative leg is also 14.4 volts.

Armed with these three laws, you can (at least in theory) analyze any DC circuit built up out of voltage or current sources and resistances and determine the voltage at any point and the current through any device or wire. As I recall, these laws plus opamps formed pretty much the whole of Circuits I in college.

Thanks DrewE. I understand that current will be the same no matter where it is measured in a circuit (before or after load, positive or negative side). So when 21A are flowing, I can measure that anywhere in circuit and see meter say 21 A.

What I found real puzzling is that while converter was charging at 14.4 V and pushing 21 A, but up at batteries I measured LESS voltage, 13.7v. Now, Im trying to wrap my head around this. I don't understand how according to ohms law for my circuit to still measure 21 A at batteries, but have lower volts 13.7v, only way that is possible is if resistance was lower 10 feet from converter at batteries. For ohms law math to work, (21*.685=14.4 at converter vs. 21*.653=13.7 at battery), resistance must be lower near batteries since voltage is less to still have 21 A. But that is not the case since the longer the wire the higher the resistance. And finally, if resistance was lower I would expect to see less drop so higher voltage would be measured near battery.

These laws you mention are 100% true fact , and you've got them right. And they work every time. I'm not arguing or doubting. But I'm sure confused. It's alright though, truth is I don't need my batteries to charge extra fast, more like just charge properly so they last long. Chargemaster changed to storage mode, now there is only 90MA flowing at 13.2v. So in 3 days they must be charged.

I do find this interesting, thanks for the help.

[MEXICOWANDERER]

Time for modification. Re-do the chassis negative. Both positive and chassis negative should have bus bar power distribution. Place the battery cut-off switch so it is a snap to switch. A "short to ground" has two scenarios - the first is sparks, fire, smoke. The second rendering the switch inoperative. I wouldn't have a switch on the positive side on Quicksilver for all the tea in China. It's foolish.

[Matt_Colie]

MEXICOWANDERER wrote:
Somebody

Anybody!

Call Caterpillar Quick!

And explain how they've been doing it "all wrong" for 70 years. The D-8R I looked at a year or so ago has lasers, a genuine computer and GPS all integrated. Plus shunts and energy monitors. And a BIG battery switch in the chassis negative cable.

Caterpillar got to build it from the ground up. They had a chance to make it that way.
Ground cables are usually short and not easy to get to, but the positive side is usually out in the clear. Putting the switch in the positive cable gives a place to add connections WITHOUT a stack up on the battery terminal.

Matt

[azrving]

Also consider the Peukert Effect when sizing battery banks.

You can have a .7 volt drop or even say a 1.2 volt drop over the circuit and still get the battery charged. The problem is that it's going to take longer.

As Drew said, all the energy is there but some of it is being lost as heat when the conductors are too small or other resistances are in the circuit. If you were to plug the rig in while stored and come back days later, the battery will still be charged while having the voltage drop. It will just take longer. That's why when running a generator for example you want the system to have very low voltage loss. Saves fuel, wear and noise.

Of course the same is true for solar because you are trying to extract X amount during sun hours. If a large amount is lost in resistance during the given hours then it doesn't reach the battery before sun down. If you were out boondocking for a couple days and you go plug in and your converter only goes to 13.6 volts or the wiring losses hold you at 13.6 volts, the battery will still get charged but it will just take longer.

The same is true of taking energy out with your inverter. If the wire is undersized energy will be dissipated before going to power the device.


The loss in the wiring is your gasoline and wear and being dissipated by the small wire so to speak. The noise portion of the gasoline is being absorbed by all of our ears.

Three things about resistance. 1. Length of the conductor. 2. Size of the conductor. 3. Temperature of the conductor.

The things I have told you are from a boondocking perspective. If you are plugging in after using your rig for weekends or just a night you may be fine with smallish voltage drops because time isn't an issue for you. This is not to say that a poor crimp or bad connection that causes resistance is ok. That poor crimp or bad connection could be a fire or battery explosion hazard if enough amps are pushed through it.

[DrewE]

pickjare wrote:
For my voltage drop concern: The converter went into normal mode this morning only pushing about 2 amps and 13.7 volts. The voltage and amperage was exactly the same at battery terminals as at converter connection. Strange how when charging at 21 Amps my amp measurement was exactly the same at the battery terminal as at converter connection, yet voltage was .7V lower. There has to be some electrical law that says no, if voltage is lost in a circuit somewhere, so will current, therefore current flow should have been lower. Ill have to try this again. I am going to assume for now that the .7 volt drop I saw when charging at 21 Amps is because its a long cable, perhaps it should have been made with larger gage.

But, I will continue checking connections and have plans to eliminate crimp on butt connectors. The connections I made use solder on type copper lugs. I did check voltage drop across the switch and through my 6 V battery connector cable, and the cable had 7 MV and the switch had 26MV--wouldn't both be considered acceptable? Connector cable being the 2 foot cable I made to connect 6V batteries in series. I have not done voltage drop across the entire positive and negative circuits from batteries to converter, just checked those 2 things since it is so easy.

There are a few basic electrical laws that come into play here. The first is Ohm's law, which defines the relationship between voltage and current in purely resistive circuit elements (such as wires). It states that E = I x R, where E is the voltage ("electromotive force"), I is the current, and R is the resistance. Since the resistance here is constant, the voltage drop when 2A is flowing is one-tenth that when 20A is flowing.

The second basic electrical law is Kirchhoff's current law. This states that at any junction in a circuit, the signed sum of all the currents is zero--or, put another way, the current flowing into any junction is equal to the current flowing out. Current doesn't pile up. If your circuit is a simple loop, this implies that the current is the same throughout the circuit, no matter where it's measured, as the current doesn't have any differing routes to flow through.

The third basic electrical law is Kirchhoff's voltage law. This states that, for any closed loop in a circuit, the signed sum of all the voltages around the loop is zero. If the converter is supplying 14.4 volts, then the voltage at the battery plus the voltage drop on the positive leg plus the voltage drop on the negative leg is also 14.4 volts.

Armed with these three laws, you can (at least in theory) analyze any DC circuit built up out of voltage or current sources and resistances and determine the voltage at any point and the current through any device or wire. As I recall, these laws plus opamps formed pretty much the whole of Circuits I in college.

[pickjare]

Thanks. Yes, I hope to have solar next spring. I have it all picked out and am looking forward to using it. Until then I am trying to take proper care of these batteries by using other methods like upgrading the existing converter to 4 stage and disconnecting batteries while not in use.

This weekend I'll move the switch to the positive side and make sure it's on the actual positive cable. I really want to keep it inside the trailer but I'll see. There is a lot more to these RV's than it seems isn't there. Well, at least in terms of doing things correctly.
Thanks everyone.

[time2roll]

Increase the charging loop to #4 wire to improve charging (reduce voltage drop). Battery will still charge fine just slower. Or get a second converter and mount close to the battery. 9140 is perfect for a 1000w generator although I mostly recommend solar.

Battery switch should be on the battery positive cable close to the battery. Switch really does nothing in the current position as best I can tell.

[mordecai81]

DrewE wrote:

mordecai81 wrote:
I installed my battery disconnect 18 inches from the battery on the negative line and zip-tied it to the trailer tongue. With the switch off, there is no power going to the interior of the trailer. The disconnect is fully enclosed except for the bottom where the negative cable runs in and out.

What are the negatives, so to speak, of my set-up? Sorry for the hi-jack, OP:D

Basically that you can't have circuits with chassis returns that are not disconnected with the switch. Perhaps the most important of those is the emergency breakaway trailer brake system. Often there may be other non-disconnected circuits, such as for CO and propane detectors (though arguably one would want them disconnected), for electric entry steps or a power trailer tongue jack, or for radio preset and clock memories.

Purely in terms of isolating the battery from the RV in an electrical sense, it doesn't matter one bit if you disconnect the positive or the negative.

Thanks

[mordecai81]

beemerphile1 wrote:

mordecai81 wrote:
I installed my battery disconnect 18 inches from the battery on the negative line and zip-tied it to the trailer tongue. With the switch off, there is no power going to the interior of the trailer. The disconnect is fully enclosed except for the bottom where the negative cable runs in and out.

What are the negatives, so to speak, of my set-up? Sorry for the hi-jack, OP:D

If you have a trailer and tow with the disconnect open, your required breakaway system will be inoperable and illegal.

I have a preflight checklist I use, so the switch is on whenever I tow. Valid point, though.

[beemerphile1]

mordecai81 wrote:
I installed my battery disconnect 18 inches from the battery on the negative line and zip-tied it to the trailer tongue. With the switch off, there is no power going to the interior of the trailer. The disconnect is fully enclosed except for the bottom where the negative cable runs in and out.

What are the negatives, so to speak, of my set-up? Sorry for the hi-jack, OP:D

If you have a trailer and tow with the disconnect open, your required breakaway system will be inoperable and illegal.

[pickjare]

Alright, well thanks for all the good help. It appears my battery cables run from the batteries to power distribution panel, then on to converter so by installing switch near converter I have only accomplished being able to disconnect the converter which isn't my intention. So I will move my switch to the cable between panel and batteries. That will open the main battery circuit. I will pay attention to the break-away switch and see how I can power it up always, I agree this is a good idea.

For my voltage drop concern: The converter went into normal mode this morning only pushing about 2 amps and 13.7 volts. The voltage and amperage was exactly the same at battery terminals as at converter connection. Strange how when charging at 21 Amps my amp measurement was exactly the same at the battery terminal as at converter connection, yet voltage was .7V lower. There has to be some electrical law that says no, if voltage is lost in a circuit somewhere, so will current, therefore current flow should have been lower. Ill have to try this again. I am going to assume for now that the .7 volt drop I saw when charging at 21 Amps is because its a long cable, perhaps it should have been made with larger gage. But, I will continue checking connections and have plans to eliminate crimp on butt connectors. The connections I made use solder on type copper lugs. I did check voltage drop across the switch and through my 6 V battery connector cable, and the cable had 7 MV and the switch had 26MV--wouldn't both be considered acceptable? Connector cable being the 2 foot cable I made to connect 6V batteries in series. I have not done voltage drop across the entire positive and negative circuits from batteries to converter, just checked those 2 things since it is so easy.

As far as polarity is concerned, yes it was correct. Just needed some reassurance from you all that I didn't have battery cable colors confused in my mind. If any of you ever use a clamp on type amp meter, and pay attention to whether the + sign is pointed toward the battery + side, this only applies during discharge. So when I was checking furnace blower amp draw, the + sign pointed toward battery + terminal, and the display read 6 A. However, during charging this will be reversed, I THINK... It really doesn't matter, if you don't point the sign toward its respective battery terminal the display will simply put a negative in front of your reading. The reading will still be the same, -6 A for my furnace for example. I think anyway.


And sorry Jim, my posts makes my eyes hurt too. I thank you all for the advice.

[DrewE]

mordecai81 wrote:
I installed my battery disconnect 18 inches from the battery on the negative line and zip-tied it to the trailer tongue. With the switch off, there is no power going to the interior of the trailer. The disconnect is fully enclosed except for the bottom where the negative cable runs in and out.

What are the negatives, so to speak, of my set-up? Sorry for the hi-jack, OP:D

Basically that you can't have circuits with chassis returns that are not disconnected with the switch. Perhaps the most important of those is the emergency breakaway trailer brake system. Often there may be other non-disconnected circuits, such as for CO and propane detectors (though arguably one would want them disconnected), for electric entry steps or a power trailer tongue jack, or for radio preset and clock memories.

Purely in terms of isolating the battery from the RV in an electrical sense, it doesn't matter one bit if you disconnect the positive or the negative.

[mordecai81]

I installed my battery disconnect 18 inches from the battery on the negative line and zip-tied it to the trailer tongue. With the switch off, there is no power going to the interior of the trailer. The disconnect is fully enclosed except for the bottom where the negative cable runs in and out.

What are the negatives, so to speak, of my set-up? Sorry for the hi-jack, OP:D

[3oaks]

MEXICOWANDERER wrote:
Somebody

Anybody!

Call Caterpillar Quick!

And explain how they've been doing it "all wrong" for 70 years. The D-8R I looked at a year or so ago has lasers, a genuine computer and GPS all integrated. Plus shunts and energy monitors. And a BIG battery switch in the chassis negative cable.

Not very helpful. The discussion is about RV trailers, not HD industrial machinery. :S