Solar panel terminals

[stu9000]

I took off a small 4w solar panel that had been fitted by the previous owner. rust was destroying the connections so a bit of TLC was required to get it through one more season.

Not really boat kit but last season it seemed to do a good job of trickle charging the batteries. Putting it back onto the boat there is no clear positive or negative on the wires that lead to the batteries. It isn't easy to trace them back visually either.

Does it matter which way round I connect the panel?

Would a tester help? I do have one but, as you can tell, I lack some expertise in this area.

 

[elton]

Yes it matters which way round you connect it! Is it a trick question

Test it with a voltmeter under suitable illumination, which will tell you which is the positive. Connect positive to positive, negative to negative.

 

[VicS]

I took off a small 4w solar panel that had been fitted by the previous owner. rust was destroying the connections so a bit of TLC was required to get it through one more season.

Not really boat kit but last season it seemed to do a good job of trickle charging the batteries. Putting it back onto the boat there is no clear positive or negative on the wires that lead to the batteries. It isn't easy to trace them back visually either.

Does it matter which way round I connect the panel?

Would a tester help? I do have one but, as you can tell, I lack some expertise in this area.

Yes it certainly matters. Just as you would connect an ordinary battery charger the positive must connect to positive and negative to negative

A small inexpensive multimeter is a "must have " if you are messing about with electrics.

Your meter, set to say the 20 volt DC range, will enable you to determine which is + and which is - .

A digital meter will show a minus sign in front of the reading if you connect its leads the "wrong" way round. An analogue meter will try to drive the pointer backwards off the LH end of the scale .

 

[sarabande]

the central pin of cigarette plugs and the smaller plugs is usually +ve. It does matter quite a lot which panel terminal is connected to which on the battery. +ve output to the +ve battery terminal.

If you have a small digital multimeter, choose the 0 - 20v DC range, and touch the panel terminal. If your meter +ve is on the panel +ve, the readout will not have a negative sign in front of the figures. If you have the meter leads the "wrong" way round, it will read e.g. -14.2.

Don't forget an inline fuse on the positive cabling between the panel and battery if connecting directly.


An analog (needle) meter will only give e.g. a 14.2v reading if the leads are +ve to +ve. If +ve to -ve, the needle will deflect below the Zero figure.



EDIT

Beaten to it by VicS, and not for the first time

 

[stu9000]

Hi.
Thanks for the replies.
It isn't the panel that is unclear but the wiring on the boat.
The panel was connected to these wires whcih led to the batteries.
Wires are still good but it isn't obvious which is +.
I'll follow advice given on using multimeter.

 

[nigelmercier]

My boat also has many large wires which are all black. I've replaced the heatshrink on most of them with red or black.

 

[stu9000]

Finally got back on board yesterday and had a go at tracing the wires back to the battery. There is a white connector block which is breaking the circuit so the panel has been doing no harm, or good.

I am going to rewire the whole lot and I have been reading up on blocking diodes.

But perhaps I should go for a controller like this?
http://www.pkgreenshop.co.uk/5a-12v-solar-charge-controller-regulator.html

It would be nice to see at a glance what is going on charging wise.

I have no idea whether a 4w channel can overcharge a battery but seems a sensible feature to have.

I can't really afford a flexible panel at the moment but may get one when someone inevitable stomps on the current one. Or i might get alluminium frame panels. So it is likely that I will update my panels at some point.

Thanks

S

 

[macd]

I have no idea whether a 4w channel can overcharge a battery but [a controller] seems a sensible feature to have.

I'm assuming the spell-checker gremlin replaced "panel" with "channel".

A safe rule of thumb is that for a controller to be unnecessary the panel wattage should not exceed 10% of the Ah capacity of your battery/batteries. For 4W that equates to 40Ah, and your battery is probably at least twice that. If so, no controller is required. (Some say the relevant measure is amps not watts, in which case you're even safer without.)

 

[ghostlymoron]

It's unlikely that a 4w panel can boil a reasonably sized battery. I've had a 5w charging a 55ahr battery for years without damage. As you say the indicator lights on a regulator are useful as they tell if the battery is charging and the state of charge and if you are likely to upgrade, may be essential in future. There are loads on eBay from China, I paid about £10 only last month for a similar unit. Make sure it's a PWM type as they're much more efficient than on/off ones. The more expensive MPPT type are only worthwhile on very large systems.

 

[stu9000]

Good tip about pwm. Thanks