Electrical voltage drop solar charging battery question!

[Doodlebug]

Hi all,

 

I am totally confused.

 

I just decided to go and analyse our battery health and plugged the multimeter onto the batteries.

 

Our charging controller says our batteries are at 13v and that it is giving 3 amps of charge.

 

The multimeter says 12.7

 

The cable is 3m between the controller and the batteries and is 3mm thick

 

At only 3 amps going through 3m of cable thats 3mm thick I dont understand how I can be loosing so much voltage.

 

Could it be a battery problem?

 

In fact, to add to this,

 

I just put the multimeter on the controller and it is deffo 0.3 higher at the controller than the batteries.

 

Also, the fuse box sits between the two in the middle, so the actual cable is:

 

3mm for 1.5m and then 10 for 1.5m

 

Ooo, also I can set the cut off and the float voltage on the controller,

 

Shall I just set both 0.3v higher than they are at the moment to compensate?

 

 

I just dont understand!

 

Will moving the controller closer actually help? If it moves closer to the batteries it will only be further from the panels.

 

Thanks for any help

 

Doodlebug

Edited May 12, 2013 by Doodlebug

[smileypete]

Could be a bad crimp/loose connection, maybe measure the volt drop at different places between controller and batts to try and pin it down. Also 3mm sounds like it may be a little on the thin side, what is the wattage of your solar panels?

 

BTW is the 10mm protected by a fuse in the positive near the batt end? The fusebox halfway will only protect the cables 'downstream' as it were.

 

cheers, Pete.

~smpt~

[Doodlebug]

Ill see if I can track it down like you say.

 

The fuse box is only 1.5m away because its the only place it can be easily accessed. The battery bank is a nightmare to get to.

 

The only thing between the fuses and the batteries is one length of wire though so there isn't much that can go wrong.

 

£mm should be enough, its 30amps that it could be producing on a perfect day, but even so 0.3v at 3 amps seems excessive.

 

Ill go and look for a faulty joint now.

 

Thanks

 

Doodlebug

[Tony Brooks]

Master switch problems?

[smileypete]

Ill see if I can track it down like you say.

 

The fuse box is only 1.5m away because its the only place it can be easily accessed. The battery bank is a nightmare to get to.

 

The only thing between the fuses and the batteries is one length of wire though so there isn't much that can go wrong.

 

£mm should be enough, its 30amps that it could be producing on a perfect day, but even so 0.3v at 3 amps seems excessive.

 

Ill go and look for a faulty joint now.

 

Thanks

 

Doodlebug

 

If the controller is really capable of sourcing 30A then the cable between it and batts should be 10mm² or more, even 6mm² wouldn't really cut it. But it depends on the amount of solar connected to controller, only 400W or more would be capable of giving that much current from the controller.

 

If there's a long wire between fuses and batts, a lot can go wrong if it gets damaged and shorts the the hull or engine.

 

cheers, Pete.

~smpt~

Edited May 12, 2013 by smileypete

[Grace and Favour]

Doodlebug . . when you say you're currently using 3mm cable - - I assume you mean 3mm² cable (?)

 

You don't mean that it's measuring 3mm across the diameter - do you?

[Doodlebug]

Sorry, the cable is 3mm diameter so its 28mm2 cable.

 

The 10mm stuff is also the diameter so 314mm2

 

I havent had a chance to identify where the voltage drops off, ill see if I can get to it now, theres so much stuff stored down there its a nightmare to work on.

 

Its interesting you say the master switch. In the summer last year we had problems where, when starting the engine, it would make a clicking noise and then we would loose all power to the boat. About 5-10 minutes later it would all come back again. I investigated as much as I could and never found the cause, and the problem has gone away, but a boat engineer asked if I had looked at the master switch, he said something about heat causing it to go funny. Anyway, if it was the master switch, it could well be giving problems now.

 

Why would it be causing a voltage drop though? Do you mean the internal connections might be corroded?

 

Thanks!

[Paul C]

Sorry, the cable is 3mm diameter so its 28mm2 cable.

 

The 10mm stuff is also the diameter so 314mm2

 

I havent had a chance to identify where the voltage drops off, ill see if I can get to it now, theres so much stuff stored down there its a nightmare to work on.

 

Where did you measure the cable? Including the insulation or not? Did you work out the cross sectional areas yourself, and if so how?

[Doodlebug]

I hate electronics sometimes, i've checked at the fuse box, half way between the two, and its currently saying

 

12.85 at the controlled

12.7 at the fuse

12.65 at the batteries.

 

Just to add, there is no fuse attached at the fuse box, its just connected at the fuse box so its not a problem with a loose fuse.

Where did you measure the cable? Including the insulation or not? Did you work out the cross sectional areas yourself, and if so how?

 

I measured the diameter of the thick 10mm stuff and then used an online area of a circle calculator to work it out.

 

The 3mm stuff I know is 3mm because I only bought it a week ago, and again using the area calculator I worked out the area,

 

So it doesn't include insulation.

[Grace and Favour]

Doodlebug - - -

 

Slight problem I have with your calculations:

3mm diameter IS NOT 28mm2 cable.

 

So, if you bought 3mm cable, what is the rating printed on the side of it, please?

[Doodlebug]

I dont know, theres nothing on the side. And its not 3mm cable, ive just gone to look at the webpage I bought it from and its 4mm cable, but it doesn't tell me the cross sectional area.

 

It was this,

 

http://www.ebay.co.uk/itm/261105686626?var=560159792481&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

 

and its deffo the diameter, my micrometer says 3.864mm cross section.

 

Thanks for the help

[Chris Pink]

You are so deep in a hole of incompetence that designing a ladder to get you out again is going to be difficult.

 

4mm² is what you've bought. Twin and earth is completely unsuitable for the job and measuring to 3 decimal place is not going to help.

 

Ignoring the fact you need different cable, your voltage drop is mainly between controller and fusebox and will change according to the current but is an indication that the connections between cable to fusebox and cable to controller are not made properly (probably because the cable is the wrong sort.

 

As it's only 1.5m buy some of this (or cheaper if you can find it) http://www.ebay.co.uk/itm/Auto-Marine-THIN-WALL-Cable-6mm2-5m-long-xxx6TW-5-/110884515712?pt=UK_CarsParts_Vehicles_BoatEquipment_Accessories_SM&hash=item19d13b6f80

 

I seem to remember you're on the K and A? if so, get in touch and I'll give you some 6mm²

 

The half a volt between fuse box and battery is not good either, given that you probably have 25mm² there (roughly 10mm diameter) but if there's an isolator in the way it sounds like it's that at fault, 'yes' is the answer to corroded terminals, especially if it's one of the red flag type.

[Doodlebug]

I don't follow, at 12v, with only a couple of amps, even with only a 4mm2 cable I still shouldn't be getting such a massive voltage drop. Should I?

[Doodlebug]

Also according to the AWG table here:

 

http://en.wikipedia.org/wiki/American_wire_gauge

 

the wire I have bought is 10mm2

 

I'm not saying i'm right or your wrong, I just dont understand the conflicting information.

 

Ive checked on a number of websites and the DC voltage drop I should be getting is 0.05 not 0.3

[Richard10002]

You are so deep in a hole of incompetence that designing a ladder to get you out again is going to be difficult.

.

How eloquently put. I've been thinking of saying something similar, but couldn't think of an appropriate construct.

[Doodlebug]

To be honest I don't see how i'm that out of my depth.

 

It is set up as per the instructions. I know a lot about electronics, but haven't had any real issues with voltage drop before. So i'm asking for advice. But since no one has any real idea of what the problem is (bearing in mind that the wire is the same recommended by half a dozen website calculators) I dont think i'm any more incapable than anyone else.

 

The only suggestion that rings true is that it might be the master switch, which isn't a technical problem, its a simple malfunctioning component.

 

Sorry but I really dont see how i'm incompetent. Ive read up on all this thoroughly and can't find a solution.

 

And its not an issue with the wiring. Even with 0 amps moving between the controller and the batteries I still have the same voltage drop.

 

And to make it more confusing I am still getting 0.3v MORE voltage at the controller than the batteries.

 

So how does that work, the controller isn't giving any voltage because its dark outside.

 

 

Somehow the voltage is now increasing as it goes through the wire.

[Paul C]

Sounds like a miswire. If you're getting a voltage drop at night, then its probaby some other current, as well as the solar charging, flowing through that particular wire/circuit.

[blodger]

I don't follow, at 12v, with only a couple of amps, even with only a 4mm2 cable I still shouldn't be getting such a massive voltage drop. Should I?

 

I would take Chris Pink's advice/help and would consider leaving the isolator out of the question by wiring direct to the battery bank but including the referred to, suitable in line fuse. Such has the benefit of still charging the batts when the batts are isolated from supplying power.

As I have multiple banks I diode splt the feed to them lossing 0.3v in doing so so do not worry too much.

The batts control the voltage in the line from the controller. The controller has to be at a higher voltage for current to flow to the batts so I would expect a difference in the voltages measured at the batts and some distance away at the controller.

I understand you have a fuse box in line without a fuse, fuse or remove & relocate @ batts.

 

ETA Household mains wire is BSS forbidden for 12v wiring on boats for brevity

Edited May 12, 2013 by blodger

[smileypete]

Ha! Thank heavens Mr Pink is back. I was slowly getting exhausted with all the eleccy theads on here lately....

 

Anyway here's an Ebay source of 10mm red black cable, 2m of each will set you back £9, can't be bad:

 

http://www.ebay.co.uk/itm/TRI-RATED-CABLE-10mm-75-AMP-2-METRES-RED-CAR-BOAT-LOOM-WIRE-BS6231-PANEL-WIRE-2m-/251214035870

http://www.ebay.co.uk/itm/TRI-RATED-CABLE-10mm-75A-2-METRES-BLACK-CAR-BOAT-LOOM-WIRE-BS6231-PANEL-WIRE-2m-/251214561258

 

Or for a bit more there's 16mm but it's a bit overkill really unless your controller will be going flat out at 30A into the batts for much of the time.

 

http://www.ebay.co.uk/itm/RED-110AMP-16MM-SQ-AUTO-FLEXIBLE-BATTERY-CABLE-206-0-30-1MTR-LENGTH-BOAT-KIT-CAR-/221188891035

http://www.ebay.co.uk/itm/BLACK-110AMP-16MM-BATTERY-CABLE-HI-FLEX-1MTR-LENGTH-BOAT-KIT-CAR-/221141522724

 

BUT if you can move your controller somewhere suitable nearer the batts, then shorter cables between controller and batts can make much more difference than the longer cables in turn between panels and controller.

 

I'd definitely add a fuse near the batt end, having the wiring catch fire would be a lot worse than a tiny volt drop across a fuse.

 

cheers, Pete.

~smpt~

[Richard10002]

To be honest I don't see how i'm that out of my depth.

 

It is set up as per the instructions.

What is set up as per what instructions?

 

You bought some 4mm twin and earth cable, and seem to think it is 10mm2 cross sectional area. It's 4mm2 cross sectional area, and it's not really the right wire for the job.

 

You are adding two new batteries to what is possibly a knackered bank - and you tell us all will be fine 'cause they're being charged every day.

 

You may actually know a lot about what you are doing, but that is not how it comes across. I'm no expert, but have been "messing about" with boat electrics for 7 years now, and I can't make head or tail of what you are describing.

 

I think you have the wrong wire between controller and fuse box. I think you might have some bad connections, and I think you're batteries might be knackered. I also think that some people more knowledgeable than me think the same.

[Chris Pink]

You bought some 4mm twin and earth cable, and seem to think it is 10mm2 cross sectional area. It's 4mm2 cross sectional area, and it's not really the right wire for the job.

 

You are adding two new batteries to what is possibly a knackered bank - and you tell us all will be fine 'cause they're being charged every day.

 

I think you have the wrong wire between controller and fuse box. I think you might have some bad connections, and I think you're batteries might be knackered.

 

Elegantly put ;-) It's not the cable causing the (major part of the) voltage drop, it's the connections which could be caused by the difficulty of making a good connection with that type of cable

 

Though the state of the batteries is not really part of the voltage drop problem.

[Alex74]

The cable is 3m between the controller and the batteries and is 3mm thick

 

At only 3 amps going through 3m of cable thats 3mm thick I dont understand how I can be loosing so much voltage.

[Colin North]

At risk of sticking head above parapet...

 

I believe there is a fuse in the line at the fuse box.

 

What kind of fuse and what type of fuse-holder?

 

The smallest wire in the system is the fuse wire and there are two potential connectors, one on either side of the fuse.

 

Do you have a voltage drop across the fuse?

[Paul C]

The cable is 3m between the controller and the batteries and is 3mm thick

 

At only 3 amps going through 3m of cable thats 3mm thick I dont understand how I can be loosing so much voltage.

 

Is this the same issue or another? (Doodlebug was the OP and I couldn't find any other posts in this thread from you).

 

Is it 3m or cable or effectively 6m, because its 3m of +12V and 3m of -ve connection?

 

Is it 3mm thick or 3mm2 cross sectional area? Does the 3mm include or exclude the insulation, or the voids if you've used relatively thick strand cable (eg that mains twin & earth stuff).

 

How have you made the connections to this cable? I assume it has an inline fuse, and then goes directly to the battery.

 

Where did you measure the voltage drop?

 

Also....where is the fuse located (see Colin North's post above). Its often that fuses and their holders get corroded, for example. Sometimes simply removing and replacing the fuse (temporarily) solves the issues.

[Doodlebug]

Ok, to make things clearer i'll try and re-explain.

 

The circuit is as follows.

 

2x110ah leisure batteries (tested them and they said 12.6) || 30cm to the master switch || 1.5m of 10mm diameter (thickness of copper) battery cable || Fuse box where the 10mm goes down to 4mm WITHOUT going through a fuse (tested here and it said 12.7), it just happens there is a fuse box there, but to prevent voltage drop I tried hardwiring it straight to the 10mm cable || 1.5m of 4mm diameter cable || straight into the controller (tested here and it said 12.9) || out the controller and up to the solar panels.

 

I'll try moving the controller as close to the fuse box as I can, but if it goes with the batteries I cant look at it and check it because our batteries are so far away. There will still be voltage drop though.

 

What are the rules in terms of moving the batteries further into the living space. I assume they need to be boxed off with external vents.

 

Thanks for the help