Converter Distance.

[Jay2504]

Hello, I have a 2016 2504s. I have upgraded the electrical system by adding 3 group 31 dual purpose batteries. I also ran 4/0 cable to the shut off switch and doubled up the number 6 cable from the shut off to the circuit breaker on the frame. On the ground side I also ran 4/0 cable to a 1/2 inch stud I added to the frame. Right now I just have the factory provided converter which I think is 55 amps. I have read on this forum about people moving their converters closer to the batteries to get a faster/ better charge in a shorter amount of time. My question is this: couldn't I just leave my converter in place and run heavier cable to accomplish the same thing? On the ground side all I would have to do is run a bigger cable to the frame and use it as a wire. On the hot side, couldnt I just run heavy cable like number 2 or 4 and get the same effect as moving the converter closer? Sorry for the long post but I wanted to give details. Thanks in advance for any replies. Jay

[boondocking]

Yes, larger cable accomplishes the same thing as moving the converter closer as long as the cable is large enough for the distance.

[Jay2504]

Thanks. That is what I thought would happen. The factory supplied wire is either number 6 or 8. Haven't been under the camper in a couple of months so I'm not sure. I will add number 4 cable to the factory wiring and run a number 2 from the converter to the frame. Jay

[Herk7769]

If you are planning to run that battery stack down any large amount, you may also consider getting a larger amperage converter to keep from running the 55 amp one at maximum for hours on end when recharging.

[Jay2504]

When the stock converter dies, I am going to take Herk7769s advice and get a more powerful unit. From what I have read on here the PD brand is the way to go. I also read that some models have a override that will put the unit in full charge mode. Both sound like great ideas to cut down on generator run time. Even 75 amps divided by 3 is only 25 amps per battery, not overkill by any means. I am still a newbie by far, but the three batteries let us run the Furnance at will, use the tv, water pumps even the MaxAir fan all nite without running them down much. Charge them back up with the generator the next day while making coffee ect. Jay

[dontay]

Don't think a 75amp charger will source 75 amps to the batteries until they are charged. For 13 years I have monitored battery charging with a Xantrex Link 10 and have found that the rated charge is only "taken" by the batteries for a few seconds before the rate starts to drop very quickly. Our previous MH had a 100 amp charger and 2 6V golf cart batteries. With the batteries down to about 55-60% capacity I would start the generator and watch the charge amps go from the 80's down to around 40 in less than a minute. Then the amps would creep down to around 30 where they would stay for a long time. The cables were huge and only about 3' from charger to batteries.
Trojan battery co. says to select a charger rated at 25% of the total amp hours of the battery bank. So for the above batteries with approx. 200 amp hours capacity a 50 amp charger would be recommended.
Our current MH has 2 gp27 batteries and I installed a 45amp PD9145A converter/charger. That's way overkill for these batteries but I already had it. It starts out in the low 40's and drops to high 20's within a few minutes where it stays for a long time. A 25 amp charger would probably take the same time to fully recharge. That last bit from 10 amps to full takes over an hour so I only do that about once every two weeks or more.

[BandJCarm]

You will need to make sure that the cabling from converter to battery is rated for high amps.............

[Herk7769]

DONTAY is correct, but remember that the converter is also running all your camper's 12 volt needs while it is trying to refill the batteries, so the available amperage is shared with the camper.

As the converter "steps down" its charge rate to prevent destroying your batteries as they fill, you will get that full charge rate capability in any case.

You should only get stage 1 until the batteries have recovered to about 50% of capacity, then stage 2 till about 80% full; then stage 3 (Float or Trickle charge) till 100%. Forcing stage 1 above about 50% capacity will overheat the batteries and boil the water out of your electrolyte causing major sulphation issues and early battery death.

[Jay2504]

With LED lights and the Furnance not running probably 5-6 amps would cover the rest of the 12 volt needs when not taking a shower. I don't have an amp meter but past experience tells me that the charge rate could easily drop off very quickly whit this type of system. As soon as a voltage level is reached, the charge rate cuts back. That's why the override would be a nice feature. I could run the generator for an hour and get 14.2 volts the whole time. I think one do the things I'll look into is installing an amp gauge with a remote shunt. Jay

[325BH]

Originally Posted by Jay2504

Hello, I have a 2016 2504s. I have upgraded the electrical system by adding 3 group 31 dual purpose batteries. I also ran 4/0 cable to the shut off switch and doubled up the number 6 cable from the shut off to the circuit breaker on the frame. On the ground side I also ran 4/0 cable to a 1/2 inch stud I added to the frame. Right now I just have the factory provided converter which I think is 55 amps. I have read on this forum about people moving their converters closer to the batteries to get a faster/ better charge in a shorter amount of time. My question is this: couldn't I just leave my converter in place and run heavier cable to accomplish the same thing? On the ground side all I would have to do is run a bigger cable to the frame and use it as a wire. On the hot side, couldnt I just run heavy cable like number 2 or 4 and get the same effect as moving the converter closer? Sorry for the long post but I wanted to give details. Thanks in advance for any replies. Jay

When you say 4/0 do you mean #4? 4/0 is huge. I don't think there are any lugs in the camper that would hold 4/0.

[Jay2504]

Yes I mean 4/0. My jumpers that connect the batteries together are 1/0. Coming from the positive post of the connected batteries to the shut off underneath the propane tanks is 4/0 about 30 inches long. Going out from the batt shut off switch to the circuit breaker on the side of the frame is the orignial number 6 wire and the number 6 wire that used to run from the positive battery post to the shut off. After the breaker the positive wiring is stock for now until I can add to it. On the ground side, the negative battery cable is also 4/0 that run about 30 inches to a ground stud on the cross member that runs right under the front of the box that I made out of a 1/2 inch bolt and nuts. The original negative wire was a number 6 wire that was just attached to the frame by a self tapping screw. I am a retired Kenworth truck mechanic so I had this stuff laying around. That is why I asked the question about moving the converter, running extra cable that I have seems like less work than moving the converter. Jay

[325BH]

Wow! Some serious wire there. A bit overkill, however any length of wire that is bigger will certainly help with voltage drop issues... even if all the wire could not be upgraded.

I just replaced by converter, but left it in the same location. About 20+ feet away and I don't have time to pull off coroplast and run new bigger wire. Therefore, I too am going to start replacing sections of wire where I can. Any little bit helps.

I already welded a ground lug on the frame because the self-tapping screw for the negative battery cable was pathetic.

I noticed a lot of extra wire running from the converter to the breaker box. Convenient for pulling the breaker box out, but adds to the length which is already too far.

Sounds like you have it figured out.

As far as relocating the converter... for sure, it is usually easier to move the converter closer to the batteries and simply run 12/2 Romex to power it... than to run big-ass wire between the converter and batteries.

You may be OK with your setup though.

[Jay2504]

I am also lucky that I have no underbelly cover. You can see the wiring running along the frame. I only used 4/0 cable because I had cable that size with pre-made eyelet ends laying around from work. If I had to buy cable I would have done number 2 or 4. The only INverter that I am currently using is 300 watts for the tv, so I guess the max amps going through those cables would be the 55 amps put out by the converter at full charge if it ever got there. Jay

[Herk7769]

Originally Posted by Jay2504

I am also lucky that I have no underbelly cover. You can see the wiring running along the frame. I only used 4/0 cable because I had cable that size with pre-made eyelet ends laying around from work. If I had to buy cable I would have done number 2 or 4. The only INverter that I am currently using is 300 watts for the tv, so I guess the max amps going through those cables would be the 55 amps put out by the converter at full charge if it ever got there. Jay

Jay, If this is WAY more than you need, I apologize in advance.

OK, lets talk power here.

The "INverter" will only be drawing its amperage from the battery (not the 55 AMP CONverter) because why would you be using it if your camper's outlets are "hot" with shore power (needed to power the "CONverter").

When connected to shore power with dead batteries, the maximum charging current of 55 amps would only last until your batteries got to about 50% capacity, then the converter will switch to stage 2 and drop the amperage considerably (like down to 8 amps or so).

When Boondocking, the INverter will draw what it needs (as long as the battery can provide it) to produce its rated power (in your current case 300 watts of power). Remember that Watts is Watts (AC Watts are the same as DC Watts - ignoring minor losses in the INverter making them).

Power = Amps times Volts

300W = ? times 12 volts

Solve for Amps ( P/V = A) and you get

300 divided by 12 or 25 amps coming from the battery at full rated 300 Watt inverter power.

A 300 Watt INverter willpower a computer, some TVs, or charge a cell phone, and perhaps a combination of those depending on power draw (in AC Watts).

Required minimum wire size depends on the maximum FUSED length of wire required between the battery and the INverter and the maximum FUSED amperage required to produce the maximum rated INveter power.

Using this chart: https://www.bluesea.com/resources/1437

From the chart for (say) a 20 foot run of wire from the battery to the INverter (with no more than a 1 volt loss in the wire), and wire fused for the maximum required current of 25 amps, would require a wire diameter of only 12 gauge. Note that that same inverter located 30 feet from the battery would require you to increase the wire size to 10 gauge to keep the volts lost in the wire to a reasonable amount.

A "normal size" Group 24 Marine Type Dual Purpose battery is rated to provide about 70 Amps per hour (defined as total amps available over a 20 hour period) or a 3.5 amp load will kill that battery in 20 hours (3.5 times 20 = 70).

I gather that one day soon (since you have 3 Group 31 batteries - God bless you!), you will be adding a bigger INverter to run more stuff.

A Group 31 battery has (depending on manufacturer and construction) between 95 and 125 AH of capacity. So for calculation purposes lets use 100 amp hours each, for a "bank" of 300 AH. A 100AH rated battery will provide 5 amps of current for 20 hours (100AH).

Your 300AH Bank, putting out the 25 amps demanded by your 300 Watt inverter, would last 300/25 or 12 hours at that load (disregarding something called the Peukert Effect).

So since you have this monster battery bank, you decide to increase your INverter size to 3000 watts (thinking you can run your AC or something!).

Now you need 3000/12 or 250 amps of DC power to feed that INverter. 300/250 is about 1.2 hours (Totally ignoring the Peukert Effect at that delivery requirement). Your 4/0 wire would be perfect for 20 feet or less to carry that potential maximum load!

Realistically, your setup would work best with a 2000 Watt INverter and you should be able to run a coffee maker and watch TV while it is brewing.

Normally, you would still need to fuse the INverter for its maximum load of 2000/12 or 166.66 amps (rounding down) 150 amps. 150 amps will deliver a reliable 1800 watts without blowing the fuse. A 150 amp load only requires 1AWG wire (again with no more than a 1 volt wire loss) and you have 4/0. I would have no qualms at that wire size to fuse at 175 amps, but realize that your INverter would trip offline first if you overload the inverter's circuit.

Now, if you do use a 1500 watt coffee maker, how long will your batteries last making coffee? Great question! (Again ignoring the Peukert Effect)

Say your coffee maker runs for 15 minutes to make a pot of coffee.

1500/12 = 125 amps times .25 hours = 31.25 AmpHours.

Your 300 Amp Hour Battery bank is capable of making about 10 pots of coffee (again ignoring the Peukert Effect) before your batteries are dead.

Hope this helps!
Herk

If you decide to "go big" I highly recommend looking up the Peukert Effect as it will have a big impact on battery life at those higher power draw numbers.

[Herk7769]

So after I did all that, I realize that I missed the point completely.

You were talking about the run from the converter to the battery bank and not from the battery bank to the INverter.

(sigh)

Save some of that 4/0 for the battery to inverter run.

As a "Mea Culpa", here is the preferred wiring diagram for multiple 12 volt batteries in order to keep the load sharing about equal. For your installation, one of the two 23.2 amp batteries would be deleted.

As requested, attached is the full PDF that the "Method 2" clip came from.

The Method 3 and 4 are much better for battery balancing, but way harder to wire for the backyard mechanic and was not recommended as a "typical solution".

Herk

[Jay2504]

Herk7769, thanks for the great info! Unfortanatly, those were the only 4/0 cables that I had! You are correct that the 55 amps I was talking about was from the converter to the batteries. I definitely going to look up the peukert effect to learn more. Whenever I try to figure out a rough estimate of inverter load is to use a factor of ten. Like a 900 watt coffee machine will use roughly 90 amps out of the batteries. Usually the loss is a little less but it makes for easy figuring. My original idea with the 300 watt inverter was to run an small extra refrigerator
that I had while towing down the road. Even with 1foot long 10 gauge wires and a running TV engine it would not start the refrigerator. It will however run the tv ok. Another bad thing about my 300 watt inverter is the fact that it uses .9 amp just to be turned on. Way higher than some of the better made units. So I just pull the lighter plug when we're done watching tv. I am trying to figure out what size inverter to buy to run our needs when boondocking. Like has been discussed here maybe 2000 watt hooked to the microwave and outlets with automatic transfer switches. Whatever size I go with, I will run bigger than needed cable! My three batteries are hooked up with equal length jumpers and the posivitive and ground cables to the camper taken from each end like in the drawing. Jay