Why fit a diode inline from solar regulator

fred flintstone

fred flintstone

Joined
Jul 12, 2016
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Location
lincoln
Funster No
44,055
MH
Elddis Sunseeker 140
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Since 2007 on and off
I have bought a van with 2 small solar panels on top, approx 40w each.
They connect to a cheap regulator.
Where the wire leaves the regulator, heading for the positive side of the battery, someone has put a diode inline.
I have wired a few panels and never used a diode.
Is it anything to do with me having a Schaudt IT268-2 control unit?
The main thing is would it be ok to remove this diode from the system?
Help appreciated.

regulator.JPG
 
It's there to prevent reverse current which may damage the panels.
 
Depending where the diode is fitted it may also protect the regulator, doesn't do any harm and in operation will make no difference.
 
The intention is surely to prevent the reverse flow of current from the battery at night or when the panels are not producing power. As already said one would expect the regulator to do that or for their to be diodes in the box of tricks on the panels.

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Panels normally have a diode fitted in the panels connection box under the panel.
A 40w panel is usually such a low output it doesn't really need a diode as they are usually free standing and don't require a controller
I don't think I ever saw a mountable 40w panel.

Anyway, as a pair of panels (total 80w) are being used the charge current will be too high to omit a diode so it's been fitted at the easiest place.

Leave it in place.
 
Thanks for all your replies. I think the regulator should take care of this. It looks like one more thing to go wrong IMHO.
Thanks again
 
Yes they simply do not make regulators that allow reverse flow of current that would be stupid
Edit
And not fit for purpose
 
but they did years ago . and panels didnt have diodes on the back either.
regulators were more an on off switch thing . i have a few here .
unfortunately uk is a bit behind and missed the early years of solar.
diodes were the way 20 years ago.

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I've yet to find a regulator that says in the instructions
And by the way you'll need to buy and fit your own diode because our regulator is a piece of junk

Btw the one pictured can be found for sub £10 but that's no excuse
 
Techno said:
Yes they simply do not make regulators that allow reverse flow of current that would be stupid
Edit
And not fit for purpose
Click to expand...
That may be so Andy.....
BUT....If you have more than one panel what's to stop current from one, in full sun, pumping current into its partner which is in full shade ?
A regulator can't stop that, but looking at the pic that diode won't stop that happening either.
 
yes that is a modern one . but certainly years ago regs bought needed a diode.
like i said they reached a voltage in batteries and switched off when battery voltage fell they came on again .
panels were hundreds and regs in maroc cost about 5quid .
anyone starting on solar then would possibly stil think fit a diode.
i fitted one of the junk regs14 years ago . still have it it still works . but not in my trailer . i use it ona spare panel as a battery charger at home .
things have moved on i admit.
 
The most likely scenario is the previous owner read some misinformation on a forum about why his batteries were going flat overnight :LOL:
Yes mate you should always fit your own diode don't you know
 
or is it your lack of older knowledge ?
i,m not knocking you really you do a grand job of helping people . a credit to you.
but years ago it was normal to fit diodes . . yes today not necessary but a bit of allowance.
some may be just following the old way.
i remember seeing batteries boiling over years ago before even the simplest of regulators were around .
whole villages in morocco relied on just what ever batteries they could muster.
came back to uk and hardly anyone knew solar really worked .
how times have changed . uk is filling fields with solar and in morocco thety are turning the desert into green fields . solar is almost a thing of the past there.
 
There are two places you can fit a diode for a solar system, one is called a blocking diode and the other a bypass diode.

Blocking diodes are to stop the battery pushing current through the solar panel at night. These are essential if you don't have a regulator installed.
Bypass diodes are fitted in parallel with the solar panel but reverse polarity. These are only of use in a multiple panel install where they are installed in series. This is to prevent a single panel being shaded limiting the output of the others.

If you have a regulator like the one pictured above there is absolutely no use for a diode where they have one. Every circuit diagram I have seen for a PWM solar charge controller uses a mosfet output and these prevent the reverse flow of current by their very design.

So if you have no charge controller then yes, fit a diode for solar panels over about 12 watts. Below that the solar panels are too puny to do any damage. You can probably get away without a diode up to maybe 40 watts but I wouldn't risk it. With a charge controller this is not necessary.

I totally agree with @Techno on this one.
 
Techno said:
The most likely scenario is the previous owner read some misinformation on a forum about why his batteries were going flat overnight :LOL:
Yes mate you should always fit your own diode don't you know
Click to expand...
But at the same time it's doing no harm.
Maybe some miniscule resistance maybe but not causing problems....until it fails.
 
Techno said:
The most likely scenario is the previous owner read some misinformation on a forum about why his batteries were going flat overnight :LOL:
Yes mate you should always fit your own diode don't you know
Click to expand...
Probably got it on her ;) I did when I fited my panel
Bill

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PS: as others have said, no major loss by keeping it in there. You lose about 0.7V in forward voltage in a silicon diode from memory. At a charge current of 2 amps from a small panel Watts = IV so you will be losing 1.4 Watts from your charge controller at 2 amps.
 
yes but years ago even jim had he thought of luna panels and put a good connection to lunar panels . i wish i had kept it on my computer it was a a good one .
these youngsters dont under stand luna panels . we shall have to let them off . hee hee .
but really solar amazed me years ago morocco was full of it . i came home and was shocked it was hardly known about in uk.
when i had my vw t2 with roof tent etc it just wasnt viable but once i got the mini artic and thought about it solar was the way. watching a friend use an auto matic washing machine on nothing but solar i had to really take notice . then a dutch couple turned up with tumbler dryer . it blew my head.
the next winter i looked for panels . 200 quid second hand in morocco or 500 quid in uk for new 80watt panels .
how times have changed .
i fitted some the other day for a friend 78 quid for the panels 100wt .
why every m,home hasnt got a roof full i dont know.
mind i still have a nokia phone i bought in 2008.ha ha .
 
The physical size of that diode indicates it will almost certainly not be able to handle anything more than a couple of amps..
As long as it is working, fine, but if the system fails that would be the first place I would look !!
Most modern panels have a blocking diode built in..

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Frankly, I am not interested in the least bit in what one needed/fitted/used years ago.

I am interested in now.

I have lived in a van fulltime for nearly thirty years and have fitted and used solar panels for twenty of them.

I have never fitted an in-line diode.

Mind you, I have never had a habitation check, never weighed my van, don't use a sign thingy on my bike rack and drive in bare feet in Spain...

Just saying


JJ :cool:
 
vwalan said:
i fitted some the other day for a friend 78 quid for the panels 100wt .
why every m,home hasnt got a roof full i dont know.
mind i still have a nokia phone i bought in 2008.ha ha .
Click to expand...

Because mine's either plugged in or used every couple of days enough to charge the one leisure battery........horses for courses, I have no need to go to the expense of solar panels:)

PS....whats a diode supposed to do?
 
Slightly off topic, 40W solar panels are not going to give you anything like enough power. I would consider changing them to something a lot bigger.
 

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