Wire gauge selection

autostaretx

Erratic Member
"The thing that is confusing to me about the Tecma Thetford electrical requirements is - ..."

Ya know what i'd do? I'd call Thetford.

If they're going to write confusing/contradictory (words don't match Figure) documentation ... get them to explain it.

--dick (who has done that many many times... )
 
"The thing that is confusing to me about the Tecma Thetford electrical requirements is - ..."

Ya know what i'd do? I'd call Thetford.

If they're going to write confusing/contradictory (words don't match Figure) documentation ... get them to explain it.

--dick (who has done that many many times... )

Haha, ok, I'll give them a call. I've called them before, and while the US branch seemed friendly, the parent company was totally unresponsive. They are Italian, and there are certainly some quirky translation issues going on here and there. I just wanted to make sure I wasn't the problem! Regardless, it seems like as long as the wires are built for it, I should be able to use a 40A breaker. The same circuit powers the macerator and the water pump, and they both run at the same time, albeit for a short period of time

Thanks Dick!
 

elemental

Wherever you go, there you are.
Out of interest, how big of a battery bank do you have, and how much current does your DC-DC charger pull?
I have 224 amp-hours of deep-cycle AGM battery (2 Fullriver DC224 6 volt batteries in series). My DC-DC charger can pull a maximum of 50 amps from the vehicle; it limits aux battery charging to 30 amps. (Yes, the 50 amps it can theoretically pull is higher than the 40 amp draw limit I've seen in the MB BEG [upfitters guide]; I don't think it will be a problem in practice.)

Since I don't have the factory auxiliary battery, I take power directly from the starter battery through the NCV3 "PDC" attached to the positive post of the starter battery. My aux batteries are under the hood; my DC-DC charger goes on the driver seat base. I have a shunt directly attached to the negative post of the aux battery system to measure current flow and a temperature/voltage sensor mounted on the positive post so that it can compensate for battery temperature and voltage drop while charging.

I need to do a final length check for the cables, my current estimate is a conservative guess after my initial measurement. I am thinking of running the return cable to the local ground on the chassis in front of the rear axle, as it would be shorter than running it all the way back to the seat base. How does this impact the calculations when a part of the return is through the chassis? Do I include the length that the current runs through the sheet metal as well, or only the length of the two cables?
I don't know how to accommodate the van chassis in calculations when used as a return for the battery system. I *think* that the van chassis (assuming your ground points are tight mechanically and sound electrically) has higher ampacity than the cables, but I don't know whether that lets you reduce cable sizes. Worst case (I think) is to do the calculations/size the supply/return cables as if the return cable went all the way.

Maybe someone else who knows specifically how to handle this case could jump in?
 
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elemental

Wherever you go, there you are.
Oh - I meant to say this earlier: Make sure you get good quality marine AWG cabling (Ancor is one brand). Automotive SAE wire gauge is smaller than AWG. I have a dedicated refrigerator circuit in my van that I have to rerun; I had some folks run the 12 gauge cable for me while they were installing another component that I chose not to do myself [the only thing I haven't done myself]. When I went to hook up the refrigerator I noticed more voltage drop than I was expecting, and compared the cable to the 12 AWG cable I was running myself. The (unlabeled) cable was slightly smaller in wire thickness than my labeled 12 AWG cable; I suspect it is 12 gauge SAE cable.

(When my battery was close to 50% SOC and I had (foolishly) set the fridge to stop operating at 10.something instead of 9.something volts, the voltage sag when the refrigerator compressor kicked on was enough to cause it to immediately shutoff, then try to start up again in about 20 seconds. When I re-run the fridge circuit it I will use Ancor 10 AWG cable *and* a shorter (but less obvious and more difficult to feed through) path.)
 
Oh - I meant to say this earlier: Make sure you get good quality marine AWG cabling (Ancor is one brand). Automotive SAE wire gauge is smaller than AWG. I have a dedicated refrigerator circuit in my van that I have to rerun; I had some folks run the 12 gauge cable for me while they were installing another component that I chose not to do myself [the only thing I haven't done myself]. When I went to hook up the refrigerator I noticed more voltage drop than I was expecting, and compared the cable to the 12 AWG cable I was running myself. The (unlabeled) cable was slightly smaller in wire thickness than my labeled 12 AWG cable; I suspect it is 12 gauge SAE cable.

(When my battery was close to 50% SOC and I had (foolishly) set the fridge to stop operating at 10.something instead of 9.something volts, the voltage sag when the refrigerator compressor kicked on was enough to cause it to immediately shutoff, then try to start up again in about 20 seconds. When I re-run the fridge circuit it I will use Ancor 10 AWG cable *and* a shorter (but less obvious and more difficult to feed through) path.)

Elemental, I am planning to go with Ancor wire, but thank you for the tip. I found a reasonable source in the Maritimes (Binnacle). I've been trying to decide on a crimping tool. seems like the pneumatic ones are good, though people complain that they are actually metric, and not AWG. Do you have a particular crimper for terminal lugs that you like? Also, as I'm running the positive cable under the van, do you see any reason not to run the wire through the preexisting holes in the chassis supports? It would allow me to tuck everything up closer to the van, and I've found a nice route back to the panel. I would use grommets to make sure the wire is protected.

With cars, I find it's often the case that having someone else do the work is a compromise, even if they are professional. Nobody cares as much as you do. That being said, turning a van into an RV is pretty complicated, so you end up doing a lot of tweaking out on details, and there is no shortcut to really understanding the systems.

As for the chassis ground question I asked earlier, if I don't find an answer, I'll just go the conservative route and do the calculations as if the wire ran all the way back. For my current set up, using the wire as a power source from the auxiliary battery, it's obvious that my full circuit is the loop of wire I'm adding plus the loop of wire from the terminal under the driver's seat to the auxiliary battery under the passenger seat. When I repurpose this wire as a DC to DC charger, would this still be the case, or do I need to factor in the length of wire to the alternator? The DC to DC charger switches on when it sees the 14V+ from the alternator, so I assume there must be some voltage drop from the starter battery circuit, and then the additional drop form the DC to DC charger circuit?

Lastly, you asked a few posts back what I was doing for battery monitoring. I'm installing a Pico monitor, so I'll put a shunt next to the aux battery terminal. I'll also use the Pico to measure tank fresh, grey and black water tank levels among other things. I'm excited to get it set up, it seems like a really nice piece of kit.

Thanks again for all your insight, it is so valuable to have answers to some of these more specific questions!

Cheers
Phil
 

gltrimble

Well-known member
Took delivery today of this hydraulic wire crimper. 10 ton capacity that goes up to 2/0 wire. Should of purchased this three years ago if I had know how inexpensive it was. Spent $20 on a hammer crimper but these seem to be big improvement. Now I need to return @SprinterPauls 16 ton crimper I have been sitting on for months.

I did not run my wires through the channel holes but I did run my 3/4” drain lines through them to maintain a proper slope to the gray water tank.

 
Took delivery today of this hydraulic wire crimper. 10 ton capacity that goes up to 2/0 wire. Should of purchased this three years ago if I had know how inexpensive it was. Spent $20 on a hammer crimper but these seem to be big improvement. Now I need to return @SprinterPauls 16 ton crimper I have been sitting on for months.

I did not run my wires through the channel holes but I did run my 3/4” drain lines through them to maintain a proper slope to the gray water tank.

Lynn,

I was looking at that crimper today, do the dies say only the metric sizes on them? Do you just choose the closest one for the AWG size? I'm temped to get one.

I assume running the wires through the holes on the chassis would be fine as long as I install grommets to make sure the wires don't get damaged by the sheet metal and potentially short to ground.
 

gltrimble

Well-known member
Lynn,

I was looking at that crimper today, do the dies say only the metric sizes on them? Do you just choose the closest one for the AWG size? I'm temped to get one.

I assume running the wires through the holes on the chassis would be fine as long as I install grommets to make sure the wires don't get damaged by the sheet metal and potentially short to ground.
Yes, the dies appear to be metric. Having used the heavier duty version of this crimper, a 16 ton version, I can say it does a better job than my hammer crimper.
 

elemental

Wherever you go, there you are.
Elemental, I am planning to go with Ancor wire, but thank you for the tip. I found a reasonable source in the Maritimes (Binnacle). I've been trying to decide on a crimping tool. seems like the pneumatic ones are good, though people complain that they are actually metric, and not AWG. Do you have a particular crimper for terminal lugs that you like? Also, as I'm running the positive cable under the van, do you see any reason not to run the wire through the preexisting holes in the chassis supports? It would allow me to tuck everything up closer to the van, and I've found a nice route back to the panel. I would use grommets to make sure the wire is protected.
I paid for my large cable crimps (had someone with proper equipment make them). For my "ordinary" crimps I paired an Ancor crimper (part number 703010, single crimp ratchet tool) for AWG wire/terminals with Ancor AWG heat-shrink terminals. I needed the largest crimp size on that tool for some 8 AWG crimps I had (many tools only do the common red [22-16]/blue [16-14]/yellow [12-10] ranges). I also used this crimper for some Molex heat shrink terminals I had to use (supplied with a part I bought) even though the Molex are a double-crimp terminal that uses a different crimper/die; I made it work.

I found it worked best to a) select a good quality terminal, then b) get the crimp tool recommended by that manufacturer (and make sure your wire, terminals, and tools are in the same gauge system (SAE versus AWG). Cheap terminals simply won't work well even with a good crimper. Good terminals require the right crimper for best results. At a minimum, different crimp dies are required for a bare terminal (usually single crimp) versus an "insulated" terminal (often a "double crimp") versus a "heat-shrink" terminal (back to a "single crimp" [usually] but not the same crimp size as a bare terminal). Better results are obtained with the specific crimper recommended by the manufacturer. And there are variations like the Molex heat-shrink terminals that use a double-crimp (but *not* an "insulated terminal double-crimp") even though many heat shrink terminals use a single crimp. My background is an industry that can't work without widely-followed standards; learning about/dealing with the variety of automotive/marine electrical specifications (and lack thereof in some cases) has been interesting.

I don't know the pros/cons of routing through pre-existing holes in chassis supports. As long as the cable is properly supported and protected from chafing I would expect that approach to work.

As for the chassis ground question I asked earlier, if I don't find an answer, I'll just go the conservative route and do the calculations as if the wire ran all the way back. For my current set up, using the wire as a power source from the auxiliary battery, it's obvious that my full circuit is the loop of wire I'm adding plus the loop of wire from the terminal under the driver's seat to the auxiliary battery under the passenger seat. When I repurpose this wire as a DC to DC charger, would this still be the case, or do I need to factor in the length of wire to the alternator? The DC to DC charger switches on when it sees the 14V+ from the alternator, so I assume there must be some voltage drop from the starter battery circuit, and then the additional drop form the DC to DC charger circuit?
I would not try to factor in the length of wiring from the alternator to the aux battery where you are taking the power off for your system either now (running directly off the factory aux battery) or in the future (running a DC-DC charger from there to your own aux battery). Unless you have superconductors in your circuits, there will be resistance/voltage drops from every point A to point B run. Your goal is to achieve your desired minimum drop over the parts of the system that you control. A DC-DC charger will actually compensate for the voltage drop in a way that a straight wire can't, so technically you can use less care and still get a system that works as long as the voltage is enough to trigger the DC-DC charger (if it uses voltage as the trigger) and it doesn't try to draw so much current that the alternator can't keep up and the resulting voltage sag causes the charger to turn off. However, maximizing efficiency is a worthy goal (up to a point) and that is what you are doing by sizing the feed wire to your future DC-DC charger current draw.

Lastly, you asked a few posts back what I was doing for battery monitoring. I'm installing a Pico monitor, so I'll put a shunt next to the aux battery terminal. I'll also use the Pico to measure tank fresh, grey and black water tank levels among other things. I'm excited to get it set up, it seems like a really nice piece of kit.
Instrumentation is good; flying blind sucks. I don't have any (significant) on-board water storage, so I'm not familiar with various RV-style monitoring tools. I do know that you should make sure all of your current flow goes through the shunt; if anything other than the shunt is connected to the battery terminal, then the shunt can't measure it.
 

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