waeco wiring to trailer

Submitted: Monday, Jan 08, 2007 at 23:10

ThreadID: 41020 Views:3360 Replies:4 FollowUps:5

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grege7

Hi all,
I have just picked up a new off road camper and I asked that a 100 amphr AGM battery be put in the trailer with a live pin from the car through the 7 pin plug to charge it. On reading this forum this is obviously not going to be effective. I have booked the car in to get 6mm? wiring to an anderson plug with a solenoid set up to charge this battery.
I also have a 36 amphr waeco sealed battery which I intend to put in the back of the car with the 80 litre waeco fridge as an emergency back up and intend to upgrade the cigarette lighter socket and wiring to charge this.
As I am very new to this wiring business, my question is---- am I on the right track?
Also, there is a small anderson plug (50amp? I think) already on the trailer. Will this small plug handle this current?
One more question. Is it possible that the original charge in the new battery drained back the other way through the 7 pin plug resulting in a very dead AGM battery that was unable to be rescued?
Any advice and suggestions would be much appreciated. As I said I am a very very novice car sparky.
Many thanks
Grege7

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Reply By: Member - Matt M (ACT) - Tuesday, Jan 09, 2007 at 07:35

Tuesday, Jan 09, 2007 at 07:35

Grege7,

I am no auto electric guru, but have just returned from a 6 month trip and have a very similar setup (210 Ah batteries in the trailer running a 50 litre Waeco) and have learnt a few lessons along the way. My trailer batteries charge through the 7 pin trailer plug when the car is running using 6mm wire. I have measured the voltage drop from the solenoid under the bonnet to the batteries in the trailer and it is minimal (about 0.02v drop). That said, you can't be wrong using an anderson plug and 50amp would be fine.

My trailer batteries charge from the car (as described), from an inbuilt 240v charger when power is available and from a 70w solar panel when camping. As time went on, I was dissapointed with the charge being received from the vehicle and after 6 or so hours driving the battery level would only increase slightly. I was expecting better and the solar panel is actually much better at charging the batteries.

After some digging around and talking to other folks over a few beers, I believe that, although wire size is very inportant, my dissapointing results came about because of the solenoid setup in the car. Although the simple solenoid is a cheap and easy option, the problem is that you are only effectively trickle charging your second batteries from the cranking battery because the cranking battery acts as a buffer between the alternator and your trailer batteries. Unless there is a direct demand on the regulator, it will not produce the current you need to charge quickly.

That is my very non technical description, but with the benefit of hindsight I would have fitted a decent battery management system that protects the cranking battery as well as drawing greater current direct to the auxilliary batteries in order to charge them quicker. Interestingly, not all of the battery management systems available do this. One solution I saw was a bloke who had fitted battery isolation switches on his cranking and trailer batteries. Once the vehicle was running, he would isolate his cranking battery and his auxilliary batteries became the service batteries for his vehicle. Not sure I like the idea, but it meant that the auxilliary batteries were drawing a good charging current from the alternator because the cranking battery was out of the loop.

Interested to hear if I have missed the mark with this.

Cheers,

Matt.

AnswerID: 214175

Follow Up By: Member - Norm C (QLD) - Tuesday, Jan 09, 2007 at 11:07

Tuesday, Jan 09, 2007 at 11:07

Hi Matt. When you measures .02V drop across 6mm cable and 7 pin plug, was it under load? (ie charging drawn down battery)? I seriously doubt it.

Voltage drop is governed by 3 things; lenghth of cable, thickness of cable and current flow. With zero current flow (no load) the voltage drop will be about zero (hence your reading). Under heavy load (say 30 to 40 Amps while charging), you will be getting a pretty big voltage drop with the set up you have. As a result, your batteries will not be fully charging, or in the least it will take a very long time. As the charge builds, the current flow reduces and with it, the amout of voltage drop. So eventually, the voltage drop will reduce enough to give a fair charge, but it will take a very long time.

Problem is, unless you take SG readings, you won't even recognise the problem. You will just get a lot less usable power out of the battery than is possible with good wiring. You might get one days power from the battery, when two is easily possible.

Heaps of info on this available on this site and on the web. In my view 10mm squared cable through 50 Amp Anderson plug is the minimum.
I have run 25mm sq welding cable via 175 Amp Anderson plug (cable is too thick for 50 Amp plug). This might be overkill to some, but it highlights the issue of 'size does matter'. To the fridge, I have 10mm sq cable.

FollowupID: 474449

Follow Up By: Member - Norm C (QLD) - Tuesday, Jan 09, 2007 at 11:23

Tuesday, Jan 09, 2007 at 11:23

Hey Matt, sorry, I should have read your response better. You seem to be using an inverter (not stated) to a 240V charger (stated) to the batteries in the CT. Read it a bit fast and missed that point.

I assume the inverter is in the trailer near the charger and batteries. Otherwise you are running 240V through your car which might be a safety issue. I considered this system a couple of years ago, but decided against it due to the inbuilt inefficiencies (inverter and charger consume power). But it clearly works and I know of people who use this system.

Is your charger a 'smart' multi stage charger? If so, it should only go to float when the battery is near fully charged.
Are you getting enough input voltage (ie not too much voltage drop) to the inverter to provide a good input to the charger?

While my comments above don't apply to your set up, they do apply to others with a more conventional set up charging CT batteries via thin cable and 7 pin plug.
Sorry about the missunderstanding.

FollowupID: 474454

Follow Up By: Member - Matt M (ACT) - Sunday, Jan 14, 2007 at 11:41

Sunday, Jan 14, 2007 at 11:41

Norm,

Good point re the voltage drop under load, one I need to investigate. Your first reading was correct, I dont use an inverter to charge, the 240v charger is fitted to the trailer (20 amp smart charger) and only operates when the trailer is connected to 240v, nothing to do with the vehicle charging system.

I would never argue against good heavy wiring and quality connectors, but I still have the feeling that the simple solenoid setup does not give as good a charge to the second battery as a quality battery management system for reasons I stated. Am I correct in this assumption? My 70w solar panel uses similar size wiring (and longer cable) and does a much more effective job.

There are other factors in my case, not the least of which is that, with the fridge in the trailer, it works hardest when we are travelling. Although the Kimberley has a ventilation fan in the gullwing box, it gets better air when camping and the box is open. Also the fridge is shaded with the small front awning when caming whereas the box is usually in full sun when underway. So maybe this may contribute to the disappointing results I achieve.

Interested in your thoughts,

Matt.

FollowupID: 475510

Follow Up By: Member - Norm C (QLD) - Sunday, Jan 14, 2007 at 15:00

Sunday, Jan 14, 2007 at 15:00

Matt, I doubt that the problem is the solenoid unless it is faulty or wired incorrectly. It just acts as a switch to isolate your deep cycle batteries from the starter when the motor is not running.

To give an idea of the effect of voltage drop caused by distance, current and wire size, use this formula:
Voltage drop = Length of conductor in metres x Current in amps x 0.017 divided by conductor cross section is sq. mm
(or use one of the voltage drop calculators available on the net such as:
www.stealth316.com/2-wire-resistance.htm )

Using the formula and assuming the return distance for your set up is 14 metres (7 metres x 2) and the current draw when charging is 30 Amps.

Voltage Drop = 14 x 30 x .017 / 6
So your voltage drop is around1.2 Volts. That's way too much for effective charging or fridge operation.

If you increase your cable size to 13.5mm (6B&S) you voltage drop will reduce to around .52 Volts. This is still pretty high, but would be acceptable. As your batteries charge, the current drops and with it, the voltage drop. At 10 Amps your voltage drop will be about .176 Volts and at 5 Amps it will be about .09 Volts. So you should get a full charge in the CT batteries, just a bit slower than if they were in the engine bay.

Using my 25mm cable, my voltage drop is around .28 Volts at 30 Amps and .09 Volts at 10 Amps.

Based on this, I’d recommend that your first move should be to run 6B&S (13.5mm) cable via a 50 Amp Anderson plug.

One of the reasons your solar system is giving closer to expected results is that it operates with much lower current flows. I’m no solar expert, but it is probably putting out around 5 Amps. If so, over 14 metres (ie 7metres of twin cable), voltage drop will be .2 Volts. Much better than the 1.2 Volts from your car/trailer system.

The point you mention about the fridge working hard when driving is important. If it is running all the time, about 10 Amps (or whatever the fridge draws) of your charge current is going straight to the fridge. Is there any way you can insulate the box? Line the inside with foam sheeting?

Anyway, I’d try the larger cable first, then go from there to see if more work is required.

FollowupID: 475532

Reply By: herkman - Tuesday, Jan 09, 2007 at 08:52

Tuesday, Jan 09, 2007 at 08:52

Good morning!

Well you do not say what sort of tow vechicle you are using.

If you can fit a second battery in it, it resolves the problem of battery charging, whilst you are not using the camper. However having said that, the battery may live longer in the camper, because you avoid the high temperatures in the engine bay.

You are on the right track, but you also may like to consider a float charger to be installed in the camper as well. These are not expensive, around $60. This way you can keep that battery fully charged when the trailer is not be used. A float charger unlike a normal battery charger does not work all the time. It monitors the battery level and tops up in little amounts, and the battery life is greatly extended. We have a battery that is over three years old in our van, never needed water, and is holding the charge well.

We put the battery in the van, because we could not fit a second one in the tow vehicle.

In answer to drain back, this is not a real problem, if you wire the set up correctly.

I do suggest you need a low voltage cut out, to avoid damging the battery.

Do you have a friend who can help you, it is not complicated, but you do need to know what you are doing.

Regards

Col

AnswerID: 214189

Follow Up By: Gronk - Tuesday, Jan 09, 2007 at 11:03

Tuesday, Jan 09, 2007 at 11:03

He doesn't need a float charger because he has an AGM battery, which means that once it is fully charged it should not require "topping" up for maybe months at a time ( or even longer! ) as long as there is nothing connected to it to cause a slight drain, which in my case was a permanately connected batt charger, which is now only connected when needed.

As regards to a 7 pin plug, most of the time it should be sufficient as the pins are rated to 30A for the large round plugs ( but of course the anderson is better at 50A )
But, have you got a return earth wire back to the battery the same size as the charge wire ??? You can have a charge wire that is 100mm big, but if the return earth path is the equivilent of 3mm, then that is all the 100mm cable is capable of delivering !!

I like the idea of the 12 pin flat plugs which have the normal 7 pins plus the extra 5 pins are rated at 35A, which can be doubled up for charge and earth return, which will give a rating of 70A each, plus gives the added benifit of being able to plug in a normal 7 pin flat if you have a normal box trailer( in my case a friend lends me his ) for doing odd jobs around the home.

FollowupID: 474448

Reply By: grege7 - Tuesday, Jan 09, 2007 at 14:13

Tuesday, Jan 09, 2007 at 14:13

To all replies
Many thanks for the advice. It seems like I am on the right track and will push on with the installation. I have written done the suggestions and will talk to the 4x4 Australia people tomorrow when I drop the car in to get the work done.
I am putting the installation through a Hyundai Terracan 2.9 diesel which by the way I am very happy with after 11000 km in 2 months. Previously I have owned 3 Jackaroos in a row, and although quite happy with those too, the terracan Hioghlander has been fantastic so far. Can't believe the difference in the engine compared to the 95 3.1 diesel Jack I owned a couple of years ago.
Anyhow again thanks for all comments and am still open to more suggestions if there are any more comments to be made.
Grege7

AnswerID: 214233

Reply By: Upstart - Tuesday, Jan 09, 2007 at 23:24

Tuesday, Jan 09, 2007 at 23:24

Run 13.5 square mm cable through a Redarc isolator to 50 amp anderson plugs to your battery.

I have this setup and have just spent 3 months travelling with my CT and 60L Engel fridge/freezer without a prob.

AnswerID: 214339