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Old 10-30-2013, 09:33 AM   #1
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40 to 100 amps charging from tow vehicle

Wish me luck!! This Sterling Alternator-to-Battery charger will arrive on Wednesday. It is rated to 210 amps so I can potentially install a high output alternator and get even more juice. Not sure if my batteries can take much more though.

The tech support people said it wasn't an issue if the house batteries were not always connected. This sits between the alternator and tow vehicle/trailer batteries and sucks down the voltage to make the alternator work harder. Then it boosts voltage to do a 4 stage charging routine back to the hose batteries, temperature monitored and voltage drop corrected. It always makes sure the starter battery is charged first, or so they say. I'm a bit nervous as the chart doesn't seem to show any favoritism towards starter battery in the beginning. Hopefully that is just a marketing graph to illustrate the benefits and not actual test results.

I'll be upgrading wiring throughout my tow vehicle charging system and will set up heavy gauge cable back to the trailer via anderson connector. I may use 2 pins of my 7 way harness (12 volt positive and reverse) for the voltage and temp monitor circuits or else I will need another little connector for those wires. Probably the latter.



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Old 10-30-2013, 11:28 AM   #2
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What guage wire do you intend to use?

Tall Guy:

Be careful of which gauge wire you use. Since I am parked at TAHI I normally charge with the Xantrec, but I have installed 6 gauge in most of the tow vehicles from the alternator to the rear of the vehicles. By the time the wire routing leaves the alternator area, goes down the frame, and back to the rear bumper there may well be 30' of run.

There are many DC voltage loss/foot vs wire gauge size on the internet.

I would recommend you look at a couple of the graphs/tables prior to purchasing the wire.

PM me if you have any questions.

Dennis
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Old 10-30-2013, 12:50 PM   #3
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Charging over a long cable run is hard! I'm wanting to do a run from the high output alternator and dual truck battery's to an anderson plug on the rear of the truck also. If for nothing else but to run my little portable compressor to fill the bike tires. Here's the problem in a nutshell. As Dennis said above, you're going to need massive wire to push the relatively low voltage (14.4v) down a long run. This chart is for 5% voltage drop. Even at 5% drop, you're 14.4v, 40 amps over 25 feet will be around 13.68v at the rear connector. Can't charge anything completely with that. I'm thinking this is where that fancy looking box comes in! Looking forward to seeing your results.

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Old 10-30-2013, 03:43 PM   #4
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Nice, please post once you have it in and tell us how it works!
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Old 10-30-2013, 04:24 PM   #5
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Quote:
Originally Posted by newroswell View Post
Even at 5% drop, you're 14.4v, 40 amps over 25 feet will be around 13.68v at the rear connector. Can't charge anything completely with that. I'm thinking this is where that fancy looking box comes in!
Exactly! There will be a voltage sense line running back to the box from the batteries in the trailer and the unit is supposed to boost the voltage to allow a full charge.

I think they say this can also lower the cable size requirements (the box will simply boost more to compensate for higher loss cable) - but of course, I still need to use heavy enough cable to safely carry the amps. I probably will size for 150 to 200 amps though I won't need that unless I later upgrade to a high output alternator.

I'm not exactly sure how the voltage sense line works as they said even very thin would be fine. I guess based on that chart, there may not be much voltage drop as hardly any current will be going across. In any case, the reading the unit gets back on hat return voltage sense circuit won't be higher than the voltage at the batteries (of course, it should be a fraction or more lower than actual at batteries). So the unit will keep boosting at the box end until it gets the reading it wants back via the return sense wire.

Based on that chart, it looks like 0 to 4 gauge may be sufficient to carry 100 amps. That chart is about voltage drop though and not safe current capacity so I will have to dig a bit more to decide.
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Old 10-30-2013, 04:47 PM   #6
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I almost posted to CA_Tallguys' "12V Danfoss Fridge" post but had doubts whether peering into the crystal ball would be welcome.

I spent the evening last night sketching this out – no real beginning and no real end, not asking specific questions or doubting choices made, just going over theory.

I’d *thought* the bulk power & intelligent charging posts added in to the ‘12 Volt Refrigerator’ main topic could be split off into its own thread since more than a few readers will be introduced to these concepts for the first time…(and he’s done it, thanks CA_Tallguy)

Spoiler: three years ago I nabbed a 12 to 24V marine quality charger/converter for cheap off ebay since I’m using 24V house batteries and HAVE NOT installed it – but I’m still stuck with the same problems at 24V that exists at 12V, plus the connection being one way only. My unit attaches to the engine battery only, with alternator and battery temperature sensors with 45A maximum draw off batt/alt and 88% efficiency. It has low battery cut-out, will not draw down engine battery, etc.

Anyhow - talking about alternator output throwing heavy current into a large set of trailer batteries needs clarity on circuit requirements involved before the fancy control electronics get reviewed. To get real power takes some serious modifications.

First: stock alternators can charge around 15 to 50 amps at idle but are designed for two, three or more times engine idle speed to reach full output, so unless there is an automatic throttle adjustment just letting the engine idle 5 or 10 amp output will not be a huge benefit to a large battery bank. Compensating regulators and idle rpm high-output alternators or even a second alternator dedicated to auxiliary loads may be a solution but leaving things stock means in-transit or high-idle charging as primary to get desired alternator RPMs.

A neat point of in-transit charging is the engine is turning anyway so extra parasitic load of the alternator isn’t a plain waste of fuel – but keeping the energy in a usable form once it goes the distance to the trailer can be difficult so back to the circuits:

Let's follow the safest routing possible from the tow vehicles battery/alternator to the trailer connector - on a new F150 the total truck length can be 21' feet long bumper to bumper, subtract some for battery location but add in crossing side to side distance and following the stock wire harness the circuit length can be as much as 20 or 25 feet of wire run just to reach the hitch.

Now let us add wire length to access batteries from entry point of trailer shell (my '73 27’r battery was under bathtub, that'd be a 30' addition) of twenty feet to have a large set of batteries directly above the axles. So we’re up to 40-plus feet, alternator to house battery… Yeah, an alternative of two batteries mounted on hitch A-frame, additional batteries mounted directly behind them inside the shell, would bring the hardwire length to 26 or 30 feet.

Okay, a question – how to bridge the jump from bumper to trailer shell?
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Old 10-30-2013, 04:52 PM   #7
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* CA_Tallguy mentions Anderson Connectors. I’ve stayed with traditional trucking & agricultural connectors since they are proven, Andersons work great in protected/sheltered areas but weather and grit, grit especially if any contact grease is used, adds in trouble.

I see a Grote 2-pole 200A plug/socket for agriculture that accepts up to 4awg cable, and a Pollak 1-pole 300A unit that accepts up to 2/0 cable. Anything conventional such as heavy duty 7-pin quick-disconnects advertise 8AWG ground and 10awg conductor plus the flexible connection cable before resuming hardwired heavy conductors would be wasting a lot of power. So were adding in another four or six feet of custom heavy cable run.

Then add the losses of terminals at each junction, an inline "doomsday' fuse (that is itself a resistance heater of sorts) gets added in, etc. so the APPARENT wire run to even a battery mounted on the hitch A-frame adds in a couple more feet of apparent wire length.

Now some cable size examples using those lengths?

* CA_Tallguy’s choice of Sterling charger has a recommended wire size chart that tops out at 4 meters (13 feet) using 90mm² (4/0awg) size cable. The instructions also call for doubling alternator output amps to calculate cable amperage.

56’ stock, 46’ above the axles, 32’ on A-frame at 75, 30 and 20 Amps current at 12 Volts:

56 feet
4AWG wire 75A = 17.88 % voltage drop, at 30A = 7.15%, at 20A = 4.77%
2/0AWG wire 75A = 5.61% voltage drop, at 30A = 2.24%, at 20A = 1.5%

46 feet
4AWG wire 75A = 14.68% voltage drop, at 30A = 5.88%
2/0AWG wire 75A = 4.61% voltage drop, at 30A = 1.84%

32 feet
4AWG wire 75A = 10.22 % voltage drop, at 30A = 4.08%
2/0AWG wire 75A = 3.20% voltage drop, at 30A = 1.28%

(Percentages represent voltage at the far end of the circuit reduction; a 10% drop from 14.7V at the alternator would become 13.25 volts at the far end of the circuit.)

Okay – The cables on the vehicle have got to be an armored flexible welding style cable, keeping the conductors tight together keeps the power loop the cleanest power, and with the chance to do serious damage the cables should be routed in flexible/solid conduit to shrug off road hazard damage that would be unnoticed otherwise.

Can the sections of the tow vehicle warranty be voided if you don’t use the OEM optional second battery kit and follow the exact routing the factory does on the stock trailer harness? Maybe – just let something happen and see if they don’t spike their national dealer VIN database with the trouble source you’ve introduced. Just saying, adding something to the battery terminal versus alternator may have consequences – are we good with that?

Anyhow – The sterling looks great except its meant to be mounted in the engine compartment of a boat, the same limitation that my unit has. “Install the unit in a cool and well-ventilated position close to the alternator. Also, the installation point has to be dry and free from heavy condensation since the unit is not waterproof. Do not fit it in a closed box as this might lead to overheating of the unit and reduced performance.” There is a possibility placing the unit inside the truck engine compartment inside a splash proof but ventilated shell would work, I have no idea where best to place my charger especially since a new vehicle is in the works..
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Old 10-30-2013, 05:23 PM   #8
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thanks for the detailed responses wabbitter! There is a lot to discuss so let me just start this post to say I like your idea on a better connector so I am going to have to start looking to source something like you recommend.

Secondly, I'll respond to one of your last points first... The mounting location. Indeed this is something I've been scratching my head over. First, though the manual says clean, dry, cool, ventilated or something similar... They have other docs where they call that "wishful thinking" and say to at least try to mount low in boat engine room/compartment. That being said, this device in particular seems like it needs protection more than several other models and brands I considered. I'm planning to try to mount it under the center of the dash in my truck, where most dodges of my vintage have a large void from a fold down cup holder that always breaks at the hinge. I'm hoping it will barely squeeze in there. If not, then maybe under a seat like an audio amplifier. In any case, it's not ideal to have to route the cables through the passenger compartment but there appears to be no other option.

Another item you mention is the warranty on the vehicle, and in my case it has long expired so it's not a concern. I know that the manufacturer talks a lot about their design being careful not to muck with the systems for exactly this reason. I'm sure they had to address this because of common customer concerns. I believe this product was partly introduced as it is less invasive than hacking the alternator regulator itself. But again, in my case it doesn't matter and anyone who does care about this will need to research that for themselves.

Anyway, that's it for now as I need to review your posts again to see other things to respond to.

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Old 10-30-2013, 05:31 PM   #9
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So that was trying to get information out - the details how CS_Tallguy chooses to proceed I hope he shares here.

I'm almost thinking it'd be worth it to have a voltage booster under the hood to go to 24/36/48 VDC and transmit that back to the trailer to have it bucked down by a MPPT charger - it would not be automatic under the hood, just a power point at the bumper to be switched in manually but it would cut down on losses and circuit costs.

EDIT: afterthought - on the voltage loss example I gave of "a 10% drop from 14.7V at the alternator would become 13.25 volts at the far end of the circuit" does not mean the device at the far end would starve...

Another example, 150 watts powered by 14.7 volts draws 10.2 Amps SO the same 150 watt load powered by 13.25 volts jumps to a 11.3 Amp draw. The current rises proportionately to cover the voltage drop. And... with extra current comes extra heating giving extra resistance giving lower voltage (on a small but cumulative scale) that system wide will open fuses and overheat connections over time.

So - when throwing 60 or 80, 100 or 120 amps down a circuit the 'voltage' loses are more than pretty numbers
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Old 10-30-2013, 05:38 PM   #10
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Originally Posted by CA_Tallguy View Post
I probably will size for 150 to 200 amps though I won't need that unless I later upgrade to a high output alternator.
One problem that people tend to forget is that batteries will not take a huge fast charge without damage to them. Unless you have some massive battery bank in the trailer the batteries will simply taper off all by themselves, and the rate of charge will be much, much lower than 150 to 200 amps, no matter what you do.

Look at the Trojan battery site, and the sections on rate of charge. Learn what C20 means relative to proper battery charge rate.

Three stage chargers have a Bulk stage, this is the initial charge to bring them up quickly. When the voltage reaches the bulk set point, they drop back to an Absorption rate, which is much lower in current as the battery Absorbs current more slowly to begin to top it off. Then it goes into a float mode, which adds the last few percent of charge.

A huge charging capacity will not change the characteristics of the battery you are charging. In Bulk mode it will come up to the design voltage a bit faster maybe, even then you have to be careful of forcing things. More charge capacity will do nothing for the Absorption or float rate, nor will they speed it up.
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Old 10-30-2013, 05:54 PM   #11
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I just happened to be spending some time this afternoon thinking about wire gauge so the comments and feedback from everyone are perfect in timing.

Wabbiteer, thanks for posting the 4/0 reference from the docs. I started this afternoon thinking I'd go crazy with something like that, but then started thinking I can go a lot smaller with the voltage drop compensation. Now I'm rethinking it and may need to call the company and chat. 4/0 seems way more than is needed for the amperage alone, based on some charts I was just reviewing on the net.


They may be spec'ing that mostly for voltage drop reasons and possibly for an install without the voltage sensing wire installed. They talk about how simple this install can be (the diagram I posted is near max complexity). The unit is supposed to work with just the feed from the alternator and then to the batteries and maybe one or two other wires.


I need to think about if I want to scale back in cable if the voltage sense wire will make scaling back possible. If I do, then I basically must always use that sensing connection. I can't think of why I wouldn't be doing that anyway.


So right now I think I'm mulling over whether something between 2 awg and 2/0 might suffice. I think that range should provide more than enough amperage capacity but need to read up more as I've only done 20 mins of research on this. (Again, talking JUST about the capacity and counting on the voltage drop compensation feature to make up for line loss).


One other thing about the 4/0 reference... There are numerous cases where I've seen the company write requirements or arguments for this or that where they back off on it somewhere else like the "wishful thinking" they said somewhere else about mounting location. I did see one for wire sizing where they basically said electronics are always happier with bigger wires, when possible. Fortunately they are very easy to call for more info when in doubt.
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Old 10-30-2013, 06:06 PM   #12
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Mounting the unit inside the cab - there adds a whole bunch of potential trouble into the passenger compartment, I've seen the floor illuminated by the orange glow of shorted wiring harness at 60mph before, I can't imagine what a partial, or self-limiting short that isn't enough to open the fuse yet still at 50 or 70 amps would be like.

Trusting the extreme fast-blow fuse link there is still a bunch of cable to run safely - I vote for under-hood with a nice custom housing : )
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Old 10-30-2013, 06:09 PM   #13
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With all that it sounds like it would be easier to install an inverter in the TV and run an extension cord to the converter already in the trailer and let the converter charge the battery. Would need to disconnect the TV charge line first.
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Old 10-30-2013, 08:49 PM   #14
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Quote:
Originally Posted by idroba View Post
One problem that people tend to forget is that batteries will not take a huge fast charge without damage to them. Unless you have some massive battery bank in the trailer the batteries will simply taper off all by themselves, and the rate of charge will be much, much lower than 150 to 200 amps, no matter what you do.
I understand what you're saying. Very true. I believe that the unit is intelligent about charging and things like the temperature sensor will help charge properly. Also, I do have a decent sized battery bank and my alternator currently is only 90 or 110 amps -- so there is a big limitation to start off with. I think a good chunk goes first to the starting batteries and then the house batteries get some love. The chart seems to show the amperage tapering quickly off from the beginning as well.

The optional control panel and current shunts will let me keep an eye on things fairly precisely.

My goal is to charge quickly when possible and I think at least 50 amps is safe for my bank. Probably more. I feel this unit will charge a lot better and more kindly than the single stage charger currently installed in the trailer.
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