Voltage drop

greyhoundtom · Senior Member

Voltage drop

Baz421 · Guru

Tom some info here re cable size/length/voltage drop.

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

Q1. The cable you get with panel should be enough - check voltage at panel and at end of wire to check.

Q2. OK to connect solar via Anderson Plug and rest seems OK, not 100% sure of what you are asking. You could plug the vehicle and the solar panel (individually) into the van end of Anderson Plug if that's what you mean, but you will need to isolate/bypass the DC - DC charger I think as the panel size would not normally be sufficient.

Q3. Voltage drop is measured at the point the voltage "is used or consumed" and passes through the light, fridge etc. However when selecting the cable size to use work on the whole length of cable ie positive source to battery negative/earth point.

Hope this helps.

Cheers Baz

-- Edited by Baz421 on Monday 17th of August 2015 08:58:22 PM

greyhoundtom · Senior Member

Thanks Baz,
I read to much stuff on the net and most of the time you cop conflicting opinions and that can get very confusing.

One of the items I read stated that to calculate voltage drop you take the length of the cable in meters X current X 0.017 then devide that by the cross section area of the copper wire being used in mm.
Then it made some obscure reference to having to take both the length of the positive wire and the length of the negative wire into the calculation. At least I now know that this is exactly what I need to take into consideration.

Basically I'm trying to calculate what size wire I should be using to be able to get away with having the DC to DC charger in the tug instead of having it sitting right next to the batteries in the van.

In regard to connecting solar and the tow vehicle to the van this would never occur at the same time with the setup I'm contemplating.

Cheers,
Tom

-- Edited by greyhoundtom on Monday 17th of August 2015 09:30:04 PM

Grego · Member

Hi Tom
There are many calculators on the net to assist you with the wire-sizing. It takes the guess work out :) Search 12 volt wire sizing and you should come up with a few.
Yes you are correct the full circuit being the positive and negative can be an issue with voltage drop. Something that will help is really good earths to the chassis and again from the Van chassis and to the Vehicle chassis. That way you have the whole chassis working for you reducing potential voltage drop. I know my 2014 Ranger will only accept earth back through the chassis anyway.
I use a Matson DC to DC charger and it stated to mount it a maximum of 1.5 metres from the accessory batteries( at the rear of the van and 5 metres from the rear of the vehicle) I am not sure why but I mounted this way and it works excellently. The cable in the vehicle to the anderson plug was around 12 mm diameter which is very large in mm2 and the van has 8 mm diameter which I think is around 50mm2. I was like you and thought maybe to use one anderson plug for all power in for when I use my mobile 240 watt solar panel. I ended up running another 50 amp Anderson and wiring at the rear of the van ( near my batteries to do this. In fact I found a special on ebay which gave me 10 /50 amp anderson plugs and i have now used the lot to give a number of variables for both my vehicle and caravan. This included a heavy duty 10 metre cable to my solar as well as the lighter duty 5 metre that it came with. I also put the alligator clips on an anderson which allows me to still use these for the boat battery etc. I have anderson accessory plugs on my accessory battery in my vehicle and then I have placed them on my air pump so I don't have to open up the hood to connect this to the battery with alligator clips. I love those anderson plugs and it doesn't take long to set it all up once you get into the swing of things biggrin

Jaahn · Guru

greyhoundtom wrote:
Thanks Baz,
I read to much stuff on the net and most of the time you cop conflicting opinions and that can get very confusing.

One of the items I read stated that to calculate voltage drop you take the length of the cable in meters X current X 0.017 then devide that by the cross section area of the copper wire being used in mm.
Then it made some obscure reference to having to take both the length of the positive wire and the length of the negative wire into the calculation. At least I now know that this is exactly what I need to take into consideration.

Basically I'm trying to calculate what size wire I should be using to be able to get away with having the DC to DC charger in the tug instead of having it sitting right next to the batteries in the van.
In regard to connecting solar and the tow vehicle to the van this would never occur at the same time with the setup I'm contemplating.
Cheers,Tom
Hi Tom,
My suggestions. As Baz has already said, you have to take both of the conductors length into the calculations. The current has to get there and also get back again.
The use of a single anderson connection seems OK as said.
My suggestion is simple. Put a very generous size cable from the connection to the batteries and also from the DC-DC charger to the connecter. It will only cost another $20 or so to double the cable size and halve the voltage drop anyway. Why skimp now.
Whether the cable on the portable solar panels is good enough will be debatable as most people seem to think not. However you can plug them in and measure the voltage at the panel end and at the connecter while it is fully charging and the battery voltage is down a bit. Turn some things on to keep the voltage below the cutout voltage. See what the difference is and tell us. In full sun.
Whether a volt or two makes a difference depends on what sort of controller it has and how much sun there is and how low the battery is. No simple answer but really every volt counts when you need them. If you are loosing one and a half or two volts there it is too much when you could get it down to just a fraction of a volt.
The panels at max power are putting out around 18 volts. The actually chargings stops when it drops to 12.5 or so. That only leaves a 'window' of 5.5 volts as a working range, so you can see there are not many to loose
Jaahn
PS Grego posted while I was writing.

-- Edited by Jaahn on Monday 17th of August 2015 10:03:10 PM

Woody n Sue · Guru

Umm guys I am no expert but I have a small solar panel that started life charging a 12 v battery on an electric fence energiser this I use when the van is in the shed with the solar panel out side in the sun as there is no sun in the shed on the van roof solar panel , and when I plug it into the Anderson plug which goes to the DC to DC charger in the van it will not charge, the lights go on for a second then off and so on but do not stay on to charge the battery however when I wire it in to the solar input on the DC To DC it charges the battery nicely, so I am suggesting is that plunging a solar panel into the Anderson plug which is normally connected to the tug battery / alternator and goes to the DC to DC charger (mine is a Cetek ) will not charge up the van battery, so of using. dC to DC charger you must put the solar panel feed to the solar input on the DC to Dc charger for it to work
I do use the common earth on the Anderson plug that way I only need to run a single positive lead to the DC charger
As. Have fitted an isolator switch between the batteries an the van circuitry this little panel keeps the batteries charged up nicely
As I said I'm no expert but this is my experience
Woody

Baz421 · Guru

greyhoundtom wrote:

Then it made some obscure reference to having to take both the length of the positive wire and the length of the negative wire into the calculation. At least I now know that this is exactly what I need to take into consideration.Good Tom and take it back to battery earth rather than the chassis earth system.

Basically I'm trying to calculate what size wire I should be using to be able to get away with having the DC to DC charger in the tug instead of having it sitting right next to the batteries in the van.

In regard to connecting solar and the tow vehicle to the van this would never occur at the same time with the setup I'm contemplating Yeh I though this was the case.

Cheers,
Tom

-- Edited by greyhoundtom on Monday 17th of August 2015 09:30:04 PM

03_Troopy · Guru

And yes your calculations are correct Vd = 2 X L X I X R / A where:

Vd - is the voltage drop to be calculated (Volts)
2 - is for the pos and neg cable in the run
L - is the Length of run (Meters)
I - is the load current (Amps)
R - is the resistivity of the conductor, which is 0.017ohms for copper
A - is the crossectional conductor area of the cable (mm²)

-- Edited by 03_Troopy on Tuesday 18th of August 2015 09:26:56 AM

Phil C · Guru

Hi all,

I read a burst about volt drop and correct connection for parallel batts, I must say its not something we ever did, but we used huge dia welding cables in the battery rooms or very low resistance nyvin in our aircraft.

The circuit where the feeds come from the opposite battery in a parallel network makes sense to me, however if the interconnection leads are large enough and the feeder cables the same size I would not hesitate in saying the volt drop would be almost insignificant in the realms of milli if not micro volts.

Cheers

Ondabeach · Senior Member

Tom, is it possible for you to install the charge controller in the van near the batteries. If you do that then voltage drop won't be an issue as the voltage directly out of the panels is around 18v. The voltage out of the charge controller is the optimum charge voltage so any drop from there to your batteries is going to mean your not fully charging. Doing it this way, you can simply use the same size cables that came with your collar panels.

oldtrack123 · Guru

HI Tom

Just be aware that the actual formula can be based on EITHER" Run" length =actual distance the cables run

OR for a single core cable , so the TOTAL length of copper must be used.

Here are is a formula

VD = run length x2 x Amps x 0.0164/cable cross sectional area [mm]

PeterQ

oldtrack123 · Guru

Tom
One of the items I read stated that to calculate voltage drop you take the length of the cable in meters X current X 0.017 then devide that by the cross section area of the copper wire being used in mm.
Then it made some obscure reference to having to take both the length of the positive wire and the length of the negative wire into the calculation. At least I now know that this is exactly what I need to take into consideration.

Basically I'm trying to calculate what size wire I should be using to be able to get away with having the DC to DC charger in the tug instead of having it sitting right next to the batteries in the van.

In regard to connecting solar and the tow vehicle to the van this would never occur at the same time with the setup I'm contemplating.

Cheers,
Tom

-- Edited by greyhoundtom on Monday 17th of August 2015 09:30:04 PM

HI Tom

Having the Dc/ DC charger in the tug defeats the whole purpose

If it is to do it's job to the best it should be as close to the battery it is charging as possible

You do want it to be seeing, 'as true as possible, the BATTERY's actual voltage.

PeterQ

03_Troopy · Guru

oldtrack123 wrote:

HI Tom
Just be aware that the actual formula can be based on EITHER" Run" length =actual distance the cables run
OR for a single core cable , so the TOTAL length of copper must be used.
Here are is a formula
VD = run length x2 x Amps x 0.0164/cable cross sectional area [mm]

PeterQ

Read back up the page Peter... biggrin

greyhoundtom · Senior Member

I guess the main reason for fitting the DC to DC charger in the tug is because we currently live full time in the van, in addition because of its size it is difficult to take somewhere and have everything fitted professionally. Having it done proffesionally is just about a must at this time because I'm still strugling a bit with physical issues, and lack confidence in regard to installing everything myself.

The quote I got from an auto elec to come on site and wire up the van with just the DC to DC was $900 which I felt was a bit expensive, plus the tug then also needs to have the right wiring installed, more expense.

Wiring from the batteries to the drawbar and the appropriate Anderson plug is no problems for me to do, and then I could have just taken the tug into the auto electricians to have it wired, and some DC to DC chargers also have the circuitry to stop charging if the vehicle engine is not going which would do away with the cutout required to stop the tug battery from discharging below a given voltage which should reduce the cost of that installation.

But if it can't be done, it can't be done, and I shall have to rethink my options once again.

Thank everyone for your advice it is much appreciated.

Cheers, Tom