Voltage drop a major issue for solar charging.

A couple of recent discussions and a thread on another forum have highlighted the very dramatic effect of voltage drop in cables in solar charging rigs.

Yeh I know lots of people are aware of voltage drop in low voltage DC wiring.......if there are only 12 or 24 volts and one or two go missing, things don't work so well.

BUT when we look at battery charging in particular solar battery charging, the problem of voltage drop becomes a very serious issue.

when the difference between barely charging at all and charging at a fairly rapid rate can be less than a single volt, voltage losses in solar charging systems could be crippling your system.

A poster on a thread on another board, baught a folding solar panel charging system.....for a very cheap price knowing full well what he was buying and expecting to do a little "tuning".

As well as replacing the hinges and latches with better items and a few minor mechanical tweaks......he replaced the wiring with some considerably heavier cable.
Being someone handy with electrics he had the ability to measure output and the presence of mind to do so before and after.

Before with the package cabled as it came out of the post the performance was disappointing to say the least.....the system delivered nowhere near what the panels output should.
After replacing the wiring and with no change in anything else, the charge current delivered to the battery doubled...in fact the systems deliverd close what is should have in theory.

I had a long phone discussion with one of the exploreoz members....and I agree that he should be doing much better out of nearly 500 watts of panels on top of his motorhome....he's getting nowhere near the 20 odd amps at 24 volts that he should out of this system in full sun.

I know those of us that are informed are well aware of voltage drop but, on solar charging systems, a very small voltage drop could very serioulsy effect your charging efficiency, particularly in marginal sunlight.

Remember too that almost every manufacturer of everything is trying to save money everywhere they can....so they predictably never "go overboard" with the wiring sizes

So...if you are not happy with the charging efficiency in ya solar system...or the figures just don't seem to add up.....maybe you should look at the size of the cables.

AND they probably should be very much larger than may seem reasonable.

A fraction of a volt will chaneg how fast ya batteries charge.

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Reply By: Member - J&R - Tuesday, Apr 16, 2013 at 10:26

Tuesday, Apr 16, 2013 at 10:26
Good advice.
But let's not go overboard though. Whilst a 200 watt panel can deliver about 12 amps on a good day, that doesn't mean you need to use battery cable to run it the 4 metres to the controller. But by all means use the biggest MOST PRACTICAL cable you can afford.

Because the length of the cable runs will impact significantly on any possible voltage drop, as will cable size, connections, joints etc.

Take a look at the solar regulator. Does it use cables inside it as thick as a house brick? No. It uses small copper tracks with small copper/solder connections. And screw connections. Take a look at the connections in the rest of the system. Are they screw terminals? Yes and no.

So the lesson is to use cable as above, solder when you can, crimp as a last resort (never when exposed to weather connections or only if you seal the connection), mount regulator as close to the battery as possible and be practical in the mounting aspect. Solar panels will drop to a fraction of output if they're oriented incorrectly, and most times you cannot pick and choose the mounting position, angle and orientation.

I am about to mount 600 watts of panels on the top of an offroad trailer. Yes a serious one, capable of self sufficiency for months at a time. Every connection will be soldered.

Who wants to pull out 600, (or 400, or 200 or 120 for that matter) watts of portable panels after driving half the day then chase the sun. And what's the point of that? Might as well take advantage of the sun while driving, even if the panels aren't quite pumping out max amps.

And go a bit bigger if possible. A 200 watt system will output 12 amps in optimum conditions, but realistically about 60-70% efficiently, then for only about 6 hours of the day without having to move it around every half hour. With the price difference between a 200 watt and a 250 one only a few dollars, go for it.
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Follow Up By: The Bantam - Tuesday, Apr 16, 2013 at 12:43

Tuesday, Apr 16, 2013 at 12:43
Sorry mate but you have a couple of problems in reasoning.

I know it may cause an argument BUT

If done correctly...correct size wire for the correct sized lugs and the correct cripper used correctly..a crimp joint will be superiour to a soldered joint in every way and in every case.

The joint will be near welded, highly reliable, less subject to corrisoon and will have a lower termination resistance.

Crimp where you can, use bolt down or screw down eye terminals where you can, screw terminals only where you must and solder as a last resort.

AND never solder and crimp, and never ever solder before you put a wire in any terminal.

As for small wires inside stuff......this is normal....short wires inside equipment do not have to be heavy because they are short and present very little resistance and thus little or no voltage drop.

It is very common to run heavy wires to a terminal and then short lighter wires of a managable size into equipment items

As a soon as wires get some length involved voltage drop gets very high very quickly, and this is 20 times more of a problem at 12 volts as it is at 240 volts.

As I mention the problem escilates orders of magnitude in the charging circuit
Dropping a volt on the way to ya fridge may not be desirable and it may effect the efficiency of ya fridge, but the fridge will pretty well work just fine.

But dropping a single volt between ya solar panels and the battery can be the difference between charging well and hardly charging at all.

I do agree that practicality becomes a real issue......in 12 or 24 volts, we will never practically eliminate voltage drop......it will always effect efficiency to some degree, especially in charging circuits

We are left with using the largest wire practical in the situation.

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Follow Up By: The Bantam - Tuesday, Apr 16, 2013 at 13:10

Tuesday, Apr 16, 2013 at 13:10
Ok lets look at some real maths.

From the example of the 200watt pannel and the 4 meters cable run.

In theory the pannel should have a maximum output of around 16 amps, in reality probably around the 12 amps...fair thing.

But for convienience I will work on 15 amps.

the total cable run there and back is 8 meters.
We realy should be considering the total run between the panels and the battery...but I'll let that pass.

if this was run in 6mm automotive twinn arround 4.5mm2
that would give a voltage drop of around half a Volt....0.49 actually.
this may be acceptable for a ciggy lighter circuit running to ya fridge, but half a volt will knock ya charging arround quite a bit.

If we step up to 6mm2 solar twinn, the voltage drop works out to be about 0.4 of a Volt.....not a hell of a lot better.

if we then step up to 10mm2 solar twinn we are down to around 0.2 of a volt...that is considerably better than the first example.

stepping up to 20mm2 "Battery Cable" we get down to about 0.1 Volts.

If we double the distance or double the current we double the voltage drop.

In either of the doubled cases that 6mm automotive is looking pretty bad..we are dropping that whole volt

The 6mm2 solar twinn is not looking a hell of a lot better.

The 10mm2 we are still dropping nearly half a volt and that will be serioulsy effecting our cloudy day charging efficiency

So it does not take much to escilate up to running full sized battery cable...the 0.2Volt drop will still be effecting our cloudy day charging voltage but we come to practicality issues.

Now in the light of how some of the campers & trailers seem to be factory wired.....members will no doubt testify to the light wires and the pretty long runs that can be found........this is a very real problem...and one the sneaks up very quickly.

keep those cable runs short and realy that battery cable is not that unreasonable.

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Follow Up By: Member - J&R - Tuesday, Apr 16, 2013 at 14:52

Tuesday, Apr 16, 2013 at 14:52
No argument from me.
I know you're wrong.
FollowupID: 786838

Follow Up By: Member - J&R - Tuesday, Apr 16, 2013 at 15:06

Tuesday, Apr 16, 2013 at 15:06
The Bantam,
More detailed info from others whose jobs rely on doing it correctly first time:

Even my anecdotal information was wrong. I stood corrected for my information on the Defence Forces.
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Follow Up By: The Bantam - Tuesday, Apr 16, 2013 at 16:58

Tuesday, Apr 16, 2013 at 16:58
If ya want to argue crimping V soldering....I can burry you in references...been there had the argument several times

Those who DO rely on getting it right first time every time CRIMP.

I have been extensively trained in both....believe me when I say my soldering is beautifull, large and small......BUT I crimp where ever I can.

There are significant reliabilty problems with soldered joints in high current DC applications.

1. under situations of high resistance joints adjacent to soldered joints the soldered Joints can pull out.
Quite a few people have found this with anderson plugs when they solder them and run them near or above capacity

60/40 lead/tin solder melts at about 185C, it is significantly compromised well below that

Copper melts at over 1000C.

a properly crimped.."near welded"...copper lug on a copper wire will not fail before all the insulation has melted and dribbled off and will very likely be found in tact in the charred and smouldering mess that once was ya caravan, probably in the melted puddle that was the batteries.

2. Soldering unavoidably required fluxes, fluxes that can not be completely removed and thus promotes corrosion in the cable adjacent to the connector.

3. the heat required to solder heavy connectors compromises the insulation on PVC insulated cables...combined with #2 a good recipie for corrosion.

I have cut appart cripmed lugs that are over 30 years old and have been regularly exposed to salt water....the copper strands where corroded 2 meters up insde the insulation BUT the strands inside the crimped lug where still firmly consolidated and bright....AND this was crimped with an old style crimper far less efficient that those currently available

4. Soldering lugs onto stranded flexible cables causes the cable to become stiff and far more prone to fracture a little beyond the lug.

This is very easy to demonatrate.

Sorry but almost every forum that deals with electrics..this discussion will come up from time to time and the result will be the same.
There are those stuck in their ways that continue to insist that soldering is best.

Those of us that have learned the benifits of properly made crimp joints know what they are used in almost every high reliability application and have been for over 30 years.

In fact in many situations now soldering is specificaly excluded in many wiring specifications.

I know there are plenty out there suspicious about crimping......and there are plenty of horrible crimp joints out there.

BUT..right wire in the right lug cripmed with the right crimper using the right method and in every way and in every situation crimping is superiour.

If you are having problems.....toss that cheap pressed metal crimper and get a decent unit.....they can be had at reasonable prices these days.

FollowupID: 786850

Follow Up By: Skulldug - Tuesday, Apr 16, 2013 at 18:19

Tuesday, Apr 16, 2013 at 18:19
So - three finger twists wrapped in blue electrical tape won't make the grade?
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Follow Up By: Lex M - Tuesday, Apr 16, 2013 at 18:47

Tuesday, Apr 16, 2013 at 18:47
Nope - gotta be red or black.
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Follow Up By: Gronk - Tuesday, Apr 16, 2013 at 20:05

Tuesday, Apr 16, 2013 at 20:05
I wired trains for a few yrs ( Millenium ) and soldered lugs were not allowed...and you'll find any major industry doesn't allow it..but cables and lugs were sized correctly for each other.

But on my 4x4, I solder all my Anderson plugs because the lugs come in 16mm2 and the cable is 13.5mm2 ( or smaller depending on use ), so crimping will not give a 100% reliable joint !!....although having said that, that only applies to hydraulic hex crimpers.......the cheaper indent ones don't do a too bad a job for undersize cables , especially as it's only for low current 4x4 applications..
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Follow Up By: Rockape - Tuesday, Apr 16, 2013 at 20:59

Tuesday, Apr 16, 2013 at 20:59
It isn't a perfect world we live in and some get caught up in the perfect world.

You don't need the perfect sized lug for the cable as you can pack it with strands of copper.

All the underground hardwire lugs were used by the sparkies, quick and simple. All the trailing cable thimbles were soldered. Now this is probably the most harsh environment electrics will exist in. The 50mm trailing cables carried between 100 and 130 amps through up to 5 soldered connections over 200 metres + the distance from the sub station which maybe another 500 metres + away. They then feed a drill with a 130 metre 35 mm trailing cable. Over the years the failure rate that I can remember was nil with the soldered joints.

These trailing cables often get salt laden water in the plugs and no problems with the connections. Sparkies pull them apart, dry them out and put them back in service.

Most failure comes with people not tinning the wire first before they place it in the lug that is full of solder.

All my anderson plugs are soldered, because I don't want to pack the lugs and I can use them again. Failure rate zero and I can put more that the 50 amps through the 50 Amp anderson plug with no heating at all.

I have seen many failures of crimped lugs, especially automotive types in the high humidity and salt laden atmospheres.

Don't get to hung up on solder or crimp as all the large circuit breakers whether it be LV or HV in a main switchboard are connected to the busbars by spring loaded jaws onto the busbars.

You can't gold plate anything unless you have the dollars. I think some get to excited about what is practical and what is perfect.

The biggest problem is not using tinned wire but then again that comes back to $'s.

Again my knuckles are starting to hurt from dragging them over the rocks.

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Follow Up By: The Bantam - Tuesday, Apr 16, 2013 at 23:07

Tuesday, Apr 16, 2013 at 23:07
Yeh I've heard all these arguments before.

There are many methods of termination and still a very small number of terminations that are still soldered for good reasons.

AND those situations there will be specific methods and materials used to manage the issues

mostly the cables will already be fairly stiff and the insulation will be HDPE or some such and the terminals will be specificaly designed.

But they are not in fine stranded cables, fairly low temperature PVC insulated cables and basicly crude terminals...like we find in automotive applications.

Almost with out exception, failures in crimp lugs are because the right sized cable, in the right sized lug and the right crimper with the right method was not used.

That may seem hard but it is not..except for anderson plugs....the lugs only come in the right sizes for the cables....select the right one.....good insulated lugs accept a wide range of wire sizes.

good crimpers have dropped dramaiticaly in price in recent years.....my first ratchet crimper for insulated lugs retailed for over $200 in the day......you can buy a ratchet crimper that is adequate for $20 and something pretty decent for under$40.

I have put ratchet crimpers in the hands of several people and it has changed their attitude to crimping insulated lugs.

You can buy a passable battery lug crimper for under $100 that will do uninsulated lugs from 10mm2 to 70mm2

The lugs in the anderson plugs are one of the few commonly that are properly designed for solder...note that the ferrel is several times the length of the diameter.

even if you wanted to you would be hard pressed to find a lug properry designed for soldering these days..the tbe will be several time the diameter

When crimping an odd sized wire into a lug it is certainly permissable to double as many strands over as necessary to properly fill the terminal.

as far as the correct procedure for crimping lugs....that is far easier and very much quicker than making a proper solder joint particularly in heavy cable.

In the past I can certainly see reasons why people thaught that reliable crimping was inaccesable that is no longer the case.

As for reusing andersons...oh come on the good coppies can be had for under $6.

In this day and age there is no good reason for not making good high reliabilty crimped terminations.

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Follow Up By: Pelikan - Thursday, Apr 18, 2013 at 17:51

Thursday, Apr 18, 2013 at 17:51
The eternal debate on crimping versus soldering! My bible on this,as I have been concerned with boat wiring, is Boatowner's Mechanical and electrical Manual by Nigel Calder. He makes the point that both can be equally good as long as the soldering is done by an expert and the crimping is done by someone with a quality crimper. Most of us are not good enough at soldering, so buy a first class crimper and quality crimp lugs.
Moving on from that, I came across an excellent article on Exploroz which amongst other things gave a formula for calculating voltage drop. As I wanted to buy a Thumper battery pack I emailed Home12volt to ask them what the wiring size was on the connection kit for charging (from the vehicle system) that comes with the battery pack. They wrote back to say that it was automotive 6mm (i.e. about 4.5 square mm). They also said that charging is achieved at 35 amps and the twin core cable supplied is 5.5 m long. I suggested to them that 35 amps through an 11m circuit would cause too big a voltage drop and that they should supply more adequate cables. They then got abusive and said that the voltage drop would only be 0.02 volts. They also said that US and UK measurements of cable size in AWG (B&S) or square mm were irrelevant in Australia and that they went by Australian standards. It so happens that Australian Standards these days use square mms, but Home12volt seemingly are unaware of this.
I calculated the voltage drop at about 1.4 volts using the above mentioned formula and cross checking with the tables in Calder's book. Can one of you experts tell me if I have got this wrong. Is it me that's off the planet or this supplier?
Cheers, Peter
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Reply By: Nomadic Navara - Friday, Apr 19, 2013 at 00:15

Friday, Apr 19, 2013 at 00:15
The big mistake people make with portable panels is they accept the panels the way they are delivered with the regulator on the panel. They should be shifting the regulator to be close to the battery. 1/4 to 1/2 a volt drop between the panel and the regulator does not effect the charge rate much. However if you have that much voltage drop between the regulator and the battery is is near disastrous.
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 01:17

Friday, Apr 19, 2013 at 01:17
Hi PeterD Long time no hear.

A related question. How much of an issue is dust for the panels mounted on the roof etc?

We got our home system cleaned and there was a noticeable increase in output. We are on the outskirts of Canberra away from any industrial contamination and smoke etc. Basically a "clean" air area.

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Follow Up By: Nomadic Navara - Friday, Apr 19, 2013 at 10:00

Friday, Apr 19, 2013 at 10:00
"We are on the outskirts of Canberra away from any industrial contamination and smoke etc. Basically a "clean" air area" - yes except for the dust that blows in from the rural areas.. Our gutters seem to stay cleaner down on the coast near the power stations.

I have not made any detailed study or the muck on my panel. I used to wash it occasionally when it was near a tree in the compound . Now it's over the other side I don't worry. From what I have seen in print from those I trust, panels are largely self cleaning. After you have had them cleaned there will be a small amount of grime collect on them but a bit of rain will keep it at bay, but never completely clean.
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 13:27

Friday, Apr 19, 2013 at 13:27
That's why I put the quotes around the word "clean".

After every trip the car's roof needs a good clean just the same as the rest of the car. There isn't a lot of rain to clean them in the areas we like to visit . I would expect it to just get worse until you had the chance to clean them. Most likely when you get home.

We did consider panels but after seeing all the muck that gathers on the roof, we put a third battery under the bonnet that will suit our needs.

But I am always open to others ideas. I gather that it is a bit hard to judge if you don't clean it. No worries. I was also after ways of cleaning them. It may be cheaper than getting someone else to do it.


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Follow Up By: The Bantam - Friday, Apr 19, 2013 at 14:08

Friday, Apr 19, 2013 at 14:08
Following up the matter of regulator location...I agree that the regulator should be located as close to the batteries as possible...this is one of the basic principles or regulation....always regulate as close as possible to the load.

AND when the solar system is running at or near capacity, a fraction of a volt between the panel/s and the regulator will be neither here nor there

after all the panel/s may be outputting 17 or 18 volts.....this is why we have regulators.

when the clouds come over or you are in some other marginal situation when the panel/s are not outputting way above charging voltage.

a fraction of a volt dropped in the cables between the panel/s and the regulator will most certainly effect charging efficiency, if we are talking about a simple regulator.


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Follow Up By: The Bantam - Friday, Apr 19, 2013 at 14:13

Friday, Apr 19, 2013 at 14:13
following up on the matter of dirty pannels.

Yeh they can claim that they are "self cleaning" all they like...how much of that is comming from the advertising department rather from the engineering department.

I can tell you there is very little that does not accumulate grime, and a surprisingly small amount of dist or grime will change light transmitted.

If someone has some dirty panels and the means of measuring the output........the argument is easily proven.

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Follow Up By: oldtrack123 - Sunday, Apr 21, 2013 at 15:13

Sunday, Apr 21, 2013 at 15:13
I pretty well go along with ALL Bantam has said!!
Summed up,the effect of Voltage from in solar wiring will depend on where it occurs
[1] if between the panels & the reg it will affect the amount of charge[Amps] into the battery
The extent is dependent on how high a voltage drop , but 0.5v would not be serious ,unless you need every bit
[2]IF that 0.5V is between the reg & the battery your battery will end up in serious trouble & have a short life
It is very unlikely to ever be fully charged
0.25V is about the ABSOLUTE MAX voltage drop that should occur between battery & reg
No matter what type regulator!!

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Follow Up By: The Bantam - Sunday, Apr 21, 2013 at 21:20

Sunday, Apr 21, 2013 at 21:20
Face facts, the sun does not always shine at full brightness and all to often mobile solar systems are under capacity and in poor conditions they require every bit of help they can get.

When the regulator is wide open, but the panel/s is/are still producing good current the voltage drop between the pannel and the regulator will very much be an issue.

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Follow Up By: oldtrack123 - Tuesday, Apr 23, 2013 at 20:16

Tuesday, Apr 23, 2013 at 20:16

The voltage drop betwen reg & batteries is not so much of a problem of reducing current
The BIG problem is [unless a voltage sense wire is used] the reg see the battery SOC voltage PLUS the cable voltage drop as the battery SOC voltage
Resulting in the reg cutting back before it should!!!
Battery UNDERCHARGED ATall times

The voltage output of the solar panels is pretty consistent .

IT is the current that is mainly determined by the light /sun intensity

With A PWM reg, VD losses between panel & reg are unlikely to have much effect on output [up to 0.5V]
ut A MPPT reg will see a slightly lower WATTAGE available at its imput to convert[about 3% loss if the VD is 0.5V]

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