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.

Usually the disconnect switch is placed in the positive battery lead, I suspect because the negative is often chassis ground and it's too easy to get unwanted sneak paths around the disconnect, especially when there are some things that must be powered all the time. (For example, the emergency breakaway switch circuit for trailer electric brakes should be powered regardless of the battery disconnect state.)The current sense doesn't sound backwards to me. The current that goes out the positive lead from the converter needs to go into the negative lead, and vice-versa for the battery. (Technically, of course, the current mostly consists of electrons flowing, and as they are negatively charged it physically flows out of the negative pole of the source and into the positive. Nevertheless, by convention the sign of measurements assumes positive charge carriers. Blame Benjamin Franklin, who had no way of knowing what polarity was correct and guessed wrong.)Wiring the converter to the DC power panel is not at all unusual, but by no means universal. It does mean that with the battery disconnected, you can use the converter to power the RV systems. The alternative (which seems a little more useful to me, and actually happens to be how my RV is wired up) is to connect the converter to the battery side of the battery disconnect, which means you can recharge with the disconnect switch open but not have live RV house circuits.I think the PD 9140 doesn't have red and white leads, but two screw terminals that the maker of the RV attaches wires to. If there are red and white wires, by convention the red almost always would be the positive and the white the negative.To track down your voltage drop, measure the voltage difference between the converter and the battery in the positive wire and in the negative wire, and scrutinize the side of the circuit that has excessive voltage. Even with a relatively long wire run and possibly marginally sized wires, I would not expect a 0.7 volt drop at 21A. My hunch is that you have a poor ground connection at either the converter output or the battery ground connection...but I could very well be all wrong.

Put the switch in the positive battery cable. It's easy to have a .7 voltage drop from the power center to the battery. Check that all lugs are tight at the power center and converter connections. Be sure you have good connections to the battery and switch. Do not use a hammer crimper on any cables, use a hydraulic crimp. You may need to upgrade the wire from power center/converter to battery as it is sometimes 6 gauge. I believe I went to 4 Gauge. The farther it is from battery to converter the more voltage drop.

Put the disconnect in the positive line at the batteries. Be sure that the emergency breakaway system is connected directly to the batteries before the disconnect.

Also, for easier reading, please use paragraphs, everything running together makes my eyes blur, thanks.Jim

Pickjare, You got a lot of real good answers here. I am a ship's engineer and did a lot of pleasure boat work before the depression shut us down. Things I second: Put the battery disconnect in the positive cable.0.7 volts drop charging at 20+ amps is not a surprise. It isn't good, but it is the direct result of manufactures not spending money on copper where it is needed. My PD units (several - one is even a 9140w/wiz) have red and black terminal, the lead colors can be anything at all as long as it is not confusing. With a clamp-on meter it is easy to get confused as to the current direction, but if you are seeing over 12.7 and the correct polarity at the bank, everything is good. The fact that you started with 12.33 and saw 21A, means you do have a voltage drop in our system. Discussion of possible corrections:As Said, put the battery disconnect in the positive cable. You can have the cable from the PD there, but nothing else at all should be direct at the battery side of the switch and only put the converter there if you will want to charge the house bank in storage. Here is a useless link that everybody uses. Ancor 3% Voltage Drop The problem is, it is for 3% and it is only one way and DC circuits all have TWO conductors. So start out be doubling the conductor length. Then think about that 3%. That 3% at 14.4V is 0.43V. With your T105s (Good Choice) at 50%SOC that will be the difference between ~40amps charge rate and 25amps charge rate or about an extra 4 hours of charge time to 90% SOC. If the PD is not just the other side of the panel from the house bank, you will need to add a bunch of copper. Remember, you only have to buy it once, but you will pay for not having it as long as you keep that RV. If you ever try to recover the bank from a generator, this will make a huge difference. Sorry this is so long, but I found that when I explained the complete situation to owners, they were more receptive to correcting the problems the better way. Matt

General wiring misunderstanding on Nash22H | Good Sam Community

pickjare
Explorer
Mar 25, 2016
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
Explorer
Mar 24, 2016
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
Explorer II
Mar 24, 2016
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
Explorer
Mar 24, 2016
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
Explorer II
Mar 24, 2016
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
Explorer
Mar 24, 2016
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
Nomad
Mar 24, 2016
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
Explorer
Mar 24, 2016
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
Explorer
Mar 24, 2016
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
Explorer
Mar 24, 2016
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.