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Old 04-22-2017, 11:45 AM   #1
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Heavy Duty Charge Cable + Anderson from Mercedes GL Tow Vehicle

Howdy folks! I'm about to attempt an install of a heavy duty charging cable from a Mercedes GL350 I've recently acquired. In conjunction with this install, I'll be rewiring the the trailer to run off of a Victron Multiplus 12/3000 charger/inverter.

This is somewhat of a continuation from my goals in setting up my previous tow vehicle which ended up FAR exceeding my expectations. Almost too far. I sold that tow vehicle and now this time I don't want to have as invasive of a system on the tow vehicle side and I want to aim for my original goal of 40 to 100 amps charging rather than 100+ amps. The previous project is detailed here:
http://www.airforums.com/forums/f37/...le-112199.html

The big question I have right now: what wire size should I go with? I'm leaning towards a #1 cable because the Mercedes has VERY little extra room to route cables. The battery is PACKED in underneath the front passenger seat. I'm almost speechless looking at how they have shoved this battery in there. To me it also looks like the main battery cables are around #1. Of course they don't need to carry large currents but for very small amounts of time for the most part.

I realize that voltage drop will be an issue if I go with #1. My thinking is that may not pose too much problem because I am not going to rely on the tow vehicle to do the finer stages of battery charging at higher volts and lower current. That will be left to solar and shore power chargers. I just want to move lots of amps when the batteries need them.

Instead of using a device like an alternator-to-battery charger or a battery-to-battery charger like I did before, I am going to start off by trying a "smart combiner" type thing such as this Victron Cyrix-ct 12/24V 120 Amp Battery Combiner. Perhaps the larger version of that product.

What do you folks think about the choice of #1 wire? This is just a S.W.A.G. (silly wild a** guess). Is this safe? Effective? I figure there may be 10 feet or so of cable run on the TV side, then an Anderson connector, and I would quickly transition from #1 to 2/0 on the trailer side running back to my relocated battery bank over the trailer axles. If this setup can safely deliver "bulk" charging that is really all I am after. Later stages will be done by more specialized chargers.
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Old 04-22-2017, 03:51 PM   #2
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Cancel the above re: wire size. I am thinking about going with #2 instead of #1. #2 seems about the largest practical size to try to maneuver into the battery box on the tow vehicle. I can't believe how every inch of this Mercedes is packed with STUFF.

Just want to make sure that the wire is going to "resist" (?) enough so that too much current does not try to flow to the trailer. Not sure if "resist" is the right nomenclature. As I don't want resistance in the form of heat, wasted energy and melted battery and flaming mercedes. In my previous system, the charging device + the wiring pulled as many amps as the alternator could handle. My theory at the time was a lot of the flow was due to the ample wiring and not the device -- but I was not sure. So now I'm trying to guesstimate based on my non-professional assessment of the previous system.
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Old 04-23-2017, 08:07 AM   #3
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If I am not getting enough amps to the back (trailer) then I will probably add one of these battery to battery chargers. They are NOT cheap but we wouldn't be Airstreamers if it had to be cheap, now would we?

Sterling Battery-to-Battery Charger 12V-12V 120 Amp Input

The above unit will pull up to 120 amps back to the battery and is going to be around $600. They have a 60 amp version that is quite a bit cheaper, and also other types of battery-to-battery charger but none of them go 100+ amps like I want to get if my wiring will handle it.

With my prior experience with Sterling, the unit maxed out my alternator and seemed like it would have gone to Sterling's rated capacity if it were possible. So if you are looking to do this, keep it in mind that you need to consider where your bottleneck will be and be sure that you won't have overloading or overheating problems there.
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Old 04-23-2017, 08:11 AM   #4
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Why not throw 600 watts of pv on the trailer roof? Always charging.
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Old 04-23-2017, 09:12 AM   #5
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Got the PV up there already. Not sure how many watts but pretty much all the space I have for it. Solar doesn't do much for helping me run my AC but with my Victron equipment I can cover a reasonable chunk of AC power requirements from my alternator. For example, I could turn on my AC and continue driving, say 30 minutes before stopping for lunch. Some of the power would come from the alternator and some from the batteries. The batteries would be replenished from solar and alternator after continuing the drive after lunch.

Digging into ampacity ratings for cable, looks like I may be OK with #2 welding cable. The following page says I am good for about 160 amps staying within 3% voltage drop (just talking about the #2 segment run -- it will be lengthened with 2/0 cable) and ramping up to 10% drop for up to 210 amps.

https://www.westmarine.com/WestAdvis...e-And-Ampacity

So if using the simple Victron Cyrix combiner isn't enough, the Sterling 160 amp battery-to-battery charger should do the trick. I will be running #2 cable from the TV battery through Anderson connectors to the front of the trailer. That's where it will meet the Victron and/or Sterling devices. From there it will be 2/0 cable to the rear battery bank.

Sterling brags that they can charge batteries 4X faster than simple combiners. That does sound nice. Maybe I should have just got the Sterling unit instead of Victron combiner. I don't know if the Sterling also functions as a smart combiner through. Maybe I can use both, but I'm also thinking they could be incompatible.
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Old 04-24-2017, 02:40 PM   #6
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I like your idea of running the AC while traveling. I do this now with 4 Crown six volt batteries and a Magnum Hybrid 3000watt inverter/charger. Using the vehicle alternator to augment the solar intrigues me. What is the AMP output of a normal alternator? You should be fine with 2/0 welding cable.
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Old 04-24-2017, 10:27 PM   #7
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Interesting -- are you able to get much AC runtime with your setup?

The inverter I will be using from Victron is quite similar in specs and function to the Magnum Hybrid.

Amp output of a "normal" alternator I think is around 90 to 120 as standard but my newer mercedes has 220 amp. I think most heavy duty vehicles are going to have higher amp alternators these days.

If I were to use the Sterling 160 amp battery to battery charger, I would anticipate getting very close to that number delivered at the initial stages of charging, maybe for 10 to 30 minutes. I'm guessing this Mercedes alternator will have spare capacity after replenishing starter battery from cranking.
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Old 04-25-2017, 06:36 AM   #8
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The AC pulls 160 AMPs so I only run it enough to cool off for lunch, business break, short nap, etc. About the most I have observed from solar is <> 20 amps so it takes several full sun hours to replenish that.

Does the battery to battery charger have a charge controller built in, or do you route the cables through the inverter for that.
?
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Old 04-25-2017, 09:21 AM   #9
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All of them (the Sterling Power models) have a 4 stage charger built in. What they do is take in whatever voltage they are getting from the alternator/battery on the tow vehicle, then they convert that to whatever voltage is needed for the particular stage of charging. Check out the links in my post for more info: http://www.airforums.com/forums/f37/...ml#post1939838

One thing I didn't particularly find satisfying about the previous type of "alternator to battery" charger I was using was that it would constantly restart the charging cycle even after short stops. The entire unit was restarted with the engine so maybe that was the best they could do. Now, with the "battery to battery" chargers -- I'm not sure if they will operate the same way. Maybe they will stay powered up and be smarter about it, continuing a cycle rather than restarting all the time. I anticipate installing the "battery to battery" charger (if I actually end up installing one) in the trailer, not the tow vehicle.

Here is a fairly detailed video that explains the system from Sterling:
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Old 04-25-2017, 11:16 AM   #10
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Great info. I appreciate the video.
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Old 04-25-2017, 11:59 AM   #11
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Okay, I'll be 'that guy' who asks the question...

Why would you need a battery to battery charger? Wouldn't the vehicle's alternator charge the trailer battery through the heavy cables. It does, after all, charge the tow vehicle's battery nicely.
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Old 04-25-2017, 08:43 PM   #12
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If you watch the video provided by Tallguy it demonstrates that the TV alternator by itself only delivers 3.9 amps to the RV battery whereas the Sterling unit delivers 40 amps. Perhaps it is the wire size...I don't have an answer for why or how.
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Old 04-26-2017, 04:45 AM   #13
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Quote:
Originally Posted by trumpetguy View Post
If you watch the video provided by Tallguy it demonstrates that the TV alternator by itself only delivers 3.9 amps to the RV battery whereas the Sterling unit delivers 40 amps. Perhaps it is the wire size...I don't have an answer for why or how.
Yes, in the video the alternator delivers 3.9 amps through the puny wire in the umbilical. It's well known that not many amps can be delivered via that method.
40 amps is delivered to the RV by the battery to battery charger which is hooked up with large wires. Since most of us can't create free energy, the tow vehicle's alternator is providing those amps to the battery to battery charger, which then pushes them into the RV batteries.
Assuming the TV and the RV are both 12v systems, I'm not sure what the purpose of the battery to battery charger is. Heavy gauge wires linking the RV battery to the TV battery in parallel, through Andersen connectors, should do the same thing.
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Old 04-26-2017, 12:01 PM   #14
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Well I am going to find out because first I am going to hook up the wiring with just a simple "combiner" that will connect the batteries over heavy cables when voltage is within charging range.

But in theory, the "charger" device should be faster because it can account for voltage drop and any other reasons the voltage might not be ideal for a charge cycle. Energy moves battery cells based on which is at a higher voltage. And the higher the voltage, the faster it moves. I've heard people make analogies to water levels in two connected vessels. The water always seeks equilibrium.

So, you are correct in saying that the puny little wire in the harness is not going to pass as much charge because voltage drops quite a bit when trying to pass large amps over small wires. (And it is interesting to note that you can get a pretty accurate measure of remote voltage over tiny little wires because you are not trying to move the energy... just grabbing a reading.) The other issue with keeping voltage up is distance -- the feet between alternator and trailer battery bank actually is significant so that is why you need large wires.

Previously I used 2/0 wires and this time around I am going for #2 wires for half the distance. Substantial difference. But as I said in one of my first posts, I am not looking to do the finer end stages of charging via this mechanism. Just trying to move lots of amps at the beginning stages of charging when trailer batteries are low. I'm thinking alternator voltage of 14+ volts and trailer batteries of 12.5 volts or so.... hopefully we will see some good amps moving to the trailer under these conditions relying simply on some reasonably heavy wiring.

As I also previously said, my earlier "alternator to battery" charger system was perhaps too effective. I was a bit uncomfortable thinking about how aggressive it always wanted to be in charging as that can be hard on batteries. The company that makes the equipment reminds that "fast charging costs water" so you have to keep an extra careful eye on that if your battery technology requires it. Mine does not so I wondered if it was the best thing to subject my batteries to this.

Anyway, we'll see how it goes. Then I'll likely get itchy to install the battery-to-battery charger regardless. LOL
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Old 04-29-2017, 05:56 PM   #15
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Lightbulb 48 volt converter

I’ve given this too much thought to stay quiet any longer. If I was designing what you’re wanting to accomplish, I’d start with a 48-volt converter and either four 12V or eight 6V batteries in series. I’d run a 30A cable from the tow vehicle back to the AS and use a 12-48V converter in the tow vehicle. The converter will load your alternator and battery a whole bunch: 30A @ 48V will require 120A from your 12V side. Assuming you have a 60A alternator, it will require 60A from the battery. 60A for ½ hour will pull 30Ah from your starting battery, if it can actually supply that much; you might not get started again after stopping.
Of course, the 48V converter system would be separate from the 12V house system. I’d leave it alone or upgrade it with the usual three stage converter and bigger battery, maybe two 6V Group 31 batteries in series.
Best of luck and happy trails!
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Old 04-30-2017, 09:32 AM   #16
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Thanks for joining in the conversation Scorge-ION! I think what you describe is similar to the "battery to battery" charger system -- the idea is to create a load on the tow vehicle side to charge a bank of batteries on the trailer side. Both concepts use voltage conversion device to accomplish this. You are basically describing a "battery to battery" charger that uses 12v input and 48v charge output. Sterling does sell devices that have different input and output voltages like this. The added benefit of Sterling devices is that they integrate 4 stage charging into the voltage conversion.

As for maintaining a battery bank at 48v -- back when I was starting out with all my energy projects I remember that I did ponder this idea but in the end I think that I chickened out and decided to keep it simple and all at 12v. These days I might be more inclined to have a separate voltage for the batteries -- a simple voltage converter to feed the 12v needs should suffice -- but now I've dug in with 12v equipment purchases so for the near term I'll probably stay this way. Maybe I'll re-evaluate before doing lifepo4 or similar based batteries. Lighter gauge wiring sure would be nice!
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Old 04-30-2017, 11:16 AM   #17
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Would a 1000 watt inverter in the tow vehicle with an extension cord running back to the trailer converter make more sense?

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Old 04-30-2017, 11:42 AM   #18
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Quote:
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Would a 1000 watt inverter in the tow vehicle with an extension cord running back to the trailer converter make more sense?
This comes up from time to time but I don't think it does make sense because your voltage conversions are not 'free' as far as efficiency, and they would cost you on each side.

This isn't to say that it doesn't make sense to have parts of alternative energy systems on 120v. Solar "inverter" type installations are one example. Part of why they make sense is that they avoid making any kind of conversion at all and allow consumption of the 120v AC output directly. But for Airstream purposes, energy storage is a large component of needs, and that is done in DC.

The other thing to consider is -- where to put the equipment? In modern cars it is getting harder and harder to find space to stow something as large as an inverter. These young people these days are removing their spare tires to make room for stereo equipment. You wouldn't believe how wedged in with a shoehorn my battery is in this Mercedes! The positive terminal is well under the passenger seat. Mercedes put an angle on the bolt to loosen it to make it marginally functional for the average human being. One of the reasons I am going "battery to battery" (perhaps without any device in the middle at all) is because I don't want to be "too invasive" on the Mercedes side (as I was with the Dodge truck I just sold where I intercepted the Alternator output for my energy games).

I'll either have no "converter/charger" device in this particular branch of my system or I will have the converter ("battery to battery" charger) mounted on the trailer side.
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Old 04-30-2017, 12:17 PM   #19
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This comes up from time to time but I don't think it does make sense because your voltage conversions are not 'free' as far as efficiency, and they would cost you on each side.

This isn't to say that it doesn't make sense to have parts of alternative energy systems on 120v. Solar "inverter" type installations are one example. Part of why they make sense is that they avoid making any kind of conversion at all and allow consumption of the 120v AC output directly. But for Airstream purposes, energy storage is a large component of needs, and that is done in DC.

The other thing to consider is -- where to put the equipment? In modern cars it is getting harder and harder to find space to stow something as large as an inverter. These young people these days are removing their spare tires to make room for stereo equipment. You wouldn't believe how wedged in with a shoehorn my battery is in this Mercedes! The positive terminal is well under the passenger seat. Mercedes put an angle on the bolt to loosen it to make it marginally functional for the average human being. One of the reasons I am going "battery to battery" (perhaps without any device in the middle at all) is because I don't want to be "too invasive" on the Mercedes side (as I was with the Dodge truck I just sold where I intercepted the Alternator output for my energy games).

I'll either have no "converter/charger" device in this particular branch of my system or I will have the converter ("battery to battery" charger) mounted on the trailer side.
So there are no losses in DC to DC conversion? Didn't know that. And 50 ft of 2/0 cable makes more sense than a 12 gauge extension cord. I'm learning a lot here.

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Old 04-30-2017, 12:47 PM   #20
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the reading on the video are fake.

The volt meter AMP clamp is only for AC reading. It does not work for DC
he places the AMP clamp on the red DC line thus the reading should be zero.

DC amp reading must be placed inline with the meter. For high amp readings it uses a shunt ( just like you see on other posts). Thus i do not trust this video.

as well DC - DC is losy, more so than AC- DC. Why, this is called "double conversion" and you get losses each time your convert.

Think back; taking a firm photoand then getting it printed vs printing direct from a negative
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