Wire gauge selection

[autostaretx]

"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... )

 

[Philip Trisix]

"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]

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?

 

[elemental]

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.)

 

[Philip Trisix]

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]

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.

https://www.amazon.com/dp/B06XR8BY65/ref=cm_sw_em_r_mt_dp_hopKFb3GD4N4G?_encoding=UTF8&psc=1

 

[Philip Trisix]

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.

https://www.amazon.com/dp/B06XR8BY65/ref=cm_sw_em_r_mt_dp_hopKFb3GD4N4G?_encoding=UTF8&psc=1

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]

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]

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.

 

[Philip Trisix]

Ok, so I took all this great advice and built out my 1st phase electronics, using the 95Ah factory aux AGM battery to power these DC loads:

Pico monitor and USB ports
Maxxair Fan
Espar diesel heater
Fresh water pump
Gray water pump
Macerator pump
Fridge
Freezer

We drove the van from Montreal to San Diego, (60 hours /10 days) and then back again a few months later. I actually installed the fridge / freezer while in California, so we just used a cooler on the first leg of the trip. Without the fridge / freezer, we had about 2 days of power, so we never needed shore power. With the fridge/freezer, We had about 10 hours of power, so some nights I would turn the fridge off, and leave the freezer on, or connect to shore power (anything to keep our ice cream frozen!).

Control Panel:


Ice cream!



For the next phase of the build, I'm adding:

315Ah Lithionics LiPo battery https://lithionicsbattery.com/product/12v-315ah-e2107-gtx-battery/
Xantrex XC PRO 3000W inverter https://www.xantrex.com/power-products/inverter-chargers/freedom-xcpro.aspx
Kisae DMT1250 DC-DC charger https://www.kisaepower.com/products/dmt1250/
Kenyon Induction Cook top https://www.cookwithkenyon.com/shop/silken2-2-burner-trimline/

I'm leaving the Aux AGM battery in, as it is quite integrated with the van, and powers a small AC inverter upfront as well as some small electronics. I am planning on installing a compressor down the road, and will probably mount it in the engine bay, and connect it the the aux battery rather than the house battery (in the rear). I have 2/0 cables (fused) running from the aux battery to the DC panel in the rear of the van from the first phase of the build, and these will now be hooked to the DC-DC charger.

I have a design consideration that I'm hung up on, and could use some help:

Jump starting the van

When the starter battery goes flat, it would be nice to be able to use the aux (AGM) battery or the house (lithium) battery to jump start the van. If were to use the factory aux battery, I would need to combine the batteries. I've heard some sprinters RVs have a button on the dash, which I believe just turns on the combiner relay to connect the two batteries (the one that combines them for charging purposes when the van is running). I've heard some people say that this combined circuit isn't really meant to be used to start the vehicle, and shouldn't really have the high current of a starter. Maybe combining the batteries for a few minutes and then releasing the button before attempting to start the engine is a solution to this concern, but it probably means limited success. Another issue with this set up would be that I'm relying on the aux battery to be charged. It's not going to be supporting any big loads, but unless I set up a charger from the house battery, it wont be connected to shore or solar.

If I were to use the house battery (located in the rear), I could use the existing 2/0 power cable, but it would need it to be unfused to be able to support the high current of the starter, so I would need some sort of battery combine switch in the rear (to direct connect the House battery to the 2/0 cables), and another switch in the front to bypass the fuse and connect to the starter battery (instead of the aux battery, or combine the batteries). This all seems overly complicated, and slightly dangerous. Another option would be just to carry a long jumper cable to connect the post of the house battery with the post in the engine bay (probably 20 feet long or so).

A final option would be, instead of relying on a direct connect between the batteries, I could have a dc charger hooked from the house to the starter battery to keep it topped up. This seems like a pretty good option, though it might mean waiting around for an hour or so (if the charger wasn't on, or if the van was stored for a couple months).

Any thoughts on combining the two AGM batteries through the relay, combining the House battery through the 2/0 cable, just using a long jumper cable, or relying on a battery charger?

 

[marklg]

I have a boost relay that connects the house batteries to the starter battery via AWG 4 or so cable. It won't crank the starter if the starter battery is run down. If the starter battery is just run down, it will charge it up enough so it can crank the starter. It takes anywhere from a few minutes to 1/2 an hour if the starter battery is down so far it will not even run the door locks.

I would not reccommend running a big cable from the house batteries to the starter unfused. That is asking for trouble and may even damage the expensive house batteries, or at least run them down too. They are not designed for high current that the glow plugs + starter pull. When my boost relay is connected, I get about 40A max to charge the starter battery. That would take 10 hours to run down that battery.

If you are not driving for months, putting a trickle charger on the starter battery is a good idea. Every time you run a lead acid battery below about 50% it is damaged and won't last long. So, my vote is trickle charger plus a boost relay with a fused, reasonable sized wire between the two batteries.

That is a large fridge. With that fridge and an induction cooktop, I am concerned your new battery will not be enough. You already underestimated once and the Lithium is an expensive purchase to find out later it was not enough. Get a coulomb counting battery monitor and figure out how many amp hours things use in a typical day, figure out how long you need to run off batteries, then choose the battery.

Regards,

Mark

 

[Philip Trisix]

Mark,

Thanks for the response. When your boost relay is connected, what is limiting the current to 40A, the starter battery? The relay? My starter battery is AGM, and I know they seem to be more sensitive to being charged properly (or at least there are chargers available specifically for AGM batteries), which is why I'd considered hardwiring an AGM charger from the house battery rather than connecting with a relay and fuse. In your case, if you left the boost relay connected and tried to start the engine, would the fuse blow?

My intention with the fridge / freezer was never to power it long term with the aux AGM, just to get back across the country...I knew it would be pushing the limits of the AGM, so I paid close attention to the current draw and state of the battery. The Pico monitor was really handy for keeping an eye on it, and making sure I didn't discharge the battery below 50%. In spring weather, the fridge / freezer combined was drawing about 4A average. The aux battery gave me about 45Ah of usable power, and the new battery is 315Ah, which is 7 times as much power. I'll definitely run through the power consumption like I did for the initial build out, thanks for the solid advice.

I should have mentioned that I'm planning to add about 350W of solar to the system, which will help on most days with the capacity. I also have a butane stove, and will wire the smaller DC loads to a battery switch to be able to power them from the aux battery incase there is an issue with the house battery, or a low power situation. It's always nice to have redundancy if things go south for whatever reason.

Cheers
Phil

 

[marklg]

Mark,

Thanks for the response. When your boost relay is connected, what is limiting the current to 40A, the starter battery? The relay? My starter battery is AGM, and I know they seem to be more sensitive to being charged properly (or at least there are chargers available specifically for AGM batteries), which is why I'd considered hardwiring an AGM charger from the house battery rather than connecting with a relay and fuse. In your case, if you left the boost relay connected and tried to start the engine, would the fuse blow?

My intention with the fridge / freezer was never to power it long term with the aux AGM, just to get back across the country...I knew it would be pushing the limits of the AGM, so I paid close attention to the current draw and state of the battery. The Pico monitor was really handy for keeping an eye on it, and making sure I didn't discharge the battery below 50%. In spring weather, the fridge / freezer combined was drawing about 4A average. The aux battery gave me about 45Ah of usable power, and the new battery is 315Ah, which is 7 times as much power. I'll definitely run through the power consumption like I did for the initial build out, thanks for the solid advice.

I should have mentioned that I'm planning to add about 350W of solar to the system, which will help on most days with the capacity. I also have a butane stove, and will wire the smaller DC loads to a battery switch to be able to power them from the aux battery incase there is an issue with the house battery, or a low power situation. It's always nice to have redundancy if things go south for whatever reason.

Cheers
Phil

The smaller wire to the boost relay is what limits the current. My boost switch is a big red guarded switch. I have a 60 A Sterling DC to DC converter that charges the house batteries from the alternator. That is not on when the boost is on, but Sterling says it can stand it for a while without damage.

Regards,

Mark

 

[Walker1271]

@Philip Trisix I echo @marklg's approach. I would not use your house batteries to start your engine. The current draw at 12V over a few meters would be significant. An average starter motor can pull 250A, combine that with multiple glow plugs and you would see a figure well over 300A. I would, as @marklg suggests, use your house battery to charge your vehicle battery in a controlled, safe manner.

I have a similar redundancy-based setup. My Vehicle Battery is connected to my house battery via an 80A fuse and double pole isolation switch. The house batteries are charged via Shore/B2B Charger or Solar/Charge Controller. This gives me the ability to leave the van for an extended period of time and maintain full charge across every battery in the vehicle. It's also cost effective.

 

[Philip Trisix]

The smaller wire to the boost relay is what limits the current. My boost switch is a big red guarded switch. I have a 60 A Sterling DC to DC converter that charges the house batteries from the alternator. That is not on when the boost is on, but Sterling says it can stand it for a while without damage.

Regards,

Mark

So you're just careful to switch off the big red switch before cranking the motor?

I don't quite understand your point about the Sterling DC to DC converter - are you just saying if you accidentally left it on while your boost relay was connected, it wouldn't fry? Your AWG 4 wire for the boost relay is separate from the Sterling wiring, right?

 

[Philip Trisix]

@Philip Trisix I echo @marklg's approach. I would not use your house batteries to start your engine. The current draw at 12V over a few meters would be significant. An average starter motor can pull 250A, combine that with multiple glow plugs and you would see a figure well over 300A. I would, as @marklg suggests, use your house battery to charge your vehicle battery in a controlled, safe manner.

I have a similar redundancy-based setup. My Vehicle Battery is connected to my house battery via an 80A fuse and double pole isolation switch. The house batteries are charged via Shore/B2B Charger or Solar/Charge Controller. This gives me the ability to leave the van for an extended period of time and maintain full charge across every battery in the vehicle. It's also cost effective.

So, when you leave your van parked, you switch the isolation switch to combine the house battery and the vehicle battery, and the solar keeps everything topped up? What would you do in the case of a flat vehicle battery on the road? I assume you would need to remember to switch this switch off before trying to start the van?

Cheers
Phil

 

[marklg]

So you're just careful to switch off the big red switch before cranking the motor?

I don't quite understand your point about the Sterling DC to DC converter - are you just saying if you accidentally left it on while your boost relay was connected, it wouldn't fry? Your AWG 4 wire for the boost relay is separate from the Sterling wiring, right?

Sterling said if I left the big red switch on, which connects the input to the output of the Sterling, that the Sterling would not fry. The Sterling also waits a couple minutes to start up, so there is plenty of time to shut off the big red switch. The Sterling remote control is on the right and I can disable it also if needed.

Sorry, I was mistaken. The contactor was original wiring when I got it. It is wired with one AWG 8. It is about 18 feet long and with 40 amps drops about a volt. So, 13V on the LiFePO4s gets me about 12V on the depleted starter battery. It has an auto reset fuse on it that seems to limit at 40 Amps. The label is unreadable. As the starter battery charges up, the current decreases. An auto reset fuse for this application seems like it works pretty well to limit the current and ease the battery back into being charged.

The Sterling is wired up 2X AWG 4 and a 100A fuse as Sterling recommends. That does not drop much voltage at all. Actual max current is about 60 Amps.


Regards,

Mark

 

[Walker1271]

So, when you leave your van parked, you switch the isolation switch to combine the house battery and the vehicle battery, and the solar keeps everything topped up? What would you do in the case of a flat vehicle battery on the road? I assume you would need to remember to switch this switch off before trying to start the van?

Cheers
Phil

@Philip Trisix thats correct, the Solar will keep the batteries topped up via the charge controller. I use the switch periodically when I need to transfer power from the house batteries to the vehicle battery, all other times it is shut off. If, for some reason the Vehicle Battery is flat, perhaps from too much cranking, I would flip the switch, give it 30-60mins, flip the switch again and crank. Alternatively, I flip the switch when I know the van will be parked up for a period of time with seldom use.

 

[mikecol]

I had lots of van battery low levels from sitting until I bought: Xantrex Echo Charger. It charges the van battery from the house source. Now all is fine and only have to worry about keeping house charged....from shore cable, alternator, or B2B chargers. One of the best things I bought for the van.

 

[Philip Trisix]

@Philip Trisix thats correct, the Solar will keep the batteries topped up via the charge controller. I use the switch periodically when I need to transfer power from the house batteries to the vehicle battery, all other times it is shut off. If, for some reason the Vehicle Battery is flat, perhaps from too much cranking, I would flip the switch, give it 30-60mins, flip the switch again and crank. Alternatively, I flip the switch when I know the van will be parked up for a period of time with seldom use.

Are your house and vehicle batteries the same type of battery? I have an AGM vehicle battery and LiPO house battery.