Now what was that electrical formula?
Yesterday was Grenadian Thanksgiving and given that almost all of the stores on the island were closed for the holiday, including the boat chandleries, it was not an ideal time to attempt to repair our non-functioning solar system. In spite of that, I still took some steps to revive it.
Non-functioning, you say? Yes. Late Wednesday afternoon, after returning from our jog around Fort Jeudy, I took note of the fact that our battery voltage was down a bit. This was in spite of the fact that the remote display for our solar charger was indicating that we had beaucoup amps coming in from the panels. Having danced this dance before, I went immediately to the fuse in the circuit to see if that was the culprit. Sure enough, not only had the 15 amp fuse burned out but the rubber case that held it was melted and charred. Not good. I should point out as well that, this is not the first time that this fuse has blown and the previous time it did so, I had to replace the fuse holder then too!
Charred and melted fuse holder — rated 15 amp max.
Why would this happen? That particular piece of the circuit was wired at a time when the boat only held 150 watts of solar panels. If I can remember my basic electrical theory, P=EI. This means that 150 watts divided by 12 volts equals 12.5 amps. Given that, a 15 amp fuse would be perfect.
When we added the additional 135 watt panel though, we upgraded the solar charger but never did anything about that fuse. The same electrical formula above shows that, now having 285 watts of solar, the circuit should be sized for 23.75 amps. No wonder the fuse blew!
16 amps coming in. Gee, I wonder why that 15A fuse blew?
Rhetorical question — don’t feel compelled to answer.
Given that the stores were closed, I couldn’t very well go shopping for a new fuse holder. I did check out the catalogues though and picked out a beefy Blue Sky one that I intend to use when I get my hands on one, which hopefully will be today. In the meantime, I simply jumped the fuse out, after increasing the size of the wire in that short run (that’s how I was able to get the above photo).
Yeah, yeah… I understand about the issues of jumping out the fuse so no lectures please. I promise not to leave the solar circuit live unless I’m on the boat monitoring it. 🙂
Mike, while you are sorting out the solar panels, take a look at MPPT controllers if you haven’t already.
The point is that solar panels produce power at 17 volts or more. Your batteries need it at 14.1 volts or thereabouts. If you did nothing, the batteries would ‘fry’. Most controllers dump the extra power as heat as they bring the voltage down. This is a waste and can cause problems.
MPPT controllers keep the wattage constant but adjust the amperage up so as to to get the voltage down from 17+ to 14.1. Similarly, in shade, evening/morning, poor conditions etc the controller brings the voltage up to 14.1 from whatever it may then be, but at a reduced amperage of course, so that the batteries continue to trickle charge at least, if they need it.
This means that you need a bigger fuse to cope with the increased amperage in strong sunlight. That is easy. And the benefit is that you get more power available on board from the same panels.
If you already know all that, then I am sorry to waste your time. Otherwise I recommend it. Even in the UK I get roughly a third more power this way.
Cheers
Mike
Hi Mike
This has been discussed here before. The salesman at the solar company that I spoke to specifically talked me out of an MMPT controller for our system. He said that they are best used when all the panels are of the same brand and type, which ours are not. This was confirmed by one of our readers, Matt Marsh, who I believe has a considerable amount of knowledge with respect to solar panels.
Even if that was not the case, there is no way I am going to take out a perfectly functioning charger, sell it at a loss and then buy an expensive new one.
My motto, learned by hard experience… If it’s working, don’t try to fix it!
Mike, before you go and up the amperage on the fuse, make sure the wires can handle it. Otherwise you may fry more than the fuse and holder.
Note that I did say that I upgraded the wire in the post. I’m going to start deducting marks for not reading thoroughly! 🙂
My mistake. I was blinded by the “jumpering the fuse” bit. You didn’t use a .22 caliber shell to jumper the fuse did you, like the Darwin candidate?
hehe… no. Truth is I didn’t really jump it. I simply removed the fuse holder from the circuit altogether, temporarily connecting the wires together.
No aluminum foil? 🙂
We were out.
Hey Mike, Don’t forget to look at your wire size. I am a big fan of oversizing wire so as to eliminate hot spots due to resistance over distance. It is no secret when you do a repair to the fuse holder the connection can never be as good as the factory. Don’t let your wire become your new fuse. If you go to a 20 amp fuse you will need to size the wire to work with that fuse. 12 aug will work of course, but check the distance recommended for that gauge. How much more is 10 aug 30 amp? Also use marine wire. Forget corrosion , marine wire is flame resistant. Just ask us, we had a fire at our main plug due to corrosion. A lot of smoke and no flame. The other guy’s comment with regards to an MPPT controller is so true. We use an Outback 60 amp. I sized everything for 60 amp and then fused it back to 30 as we have seen total amps of 19.7 . and may add more as you did. And yes our control unit will take extra power when not needed and turn it into heat that is then vented out side. When I was talking to the solar people they made a point of telling me you need to get rid of extra power or one of two things will happen . You will boil batteries dry or overheat wires. I hope something here helps as I have learned so much from you guys.
That was Brian, not Sally
Another person loses marks for not noting that I wrote that I had already upgraded the wire size. You should have blamed it on Sally.
I’ve no problem with emergency field repair. I’m sure you’ll fuse it the first chance you get. It’s people who forget those “temporary” fixes and leave them forever who get into trouble.
Agreed! Proper repair has been completed already.
Listening to all this makes me want to increase the amount I’m putting into my retirement fund. I want to cruise and enjoy, not camp and repair.
Don’t buy a boat then, Cameron. In no way will more money save you from issues like this, guaranteed!
Our boat experienced a similar problem when the previous owner upgraded from a 30 amp alternator to a 60 amp alternator. Being a forensic boat electrician, I discovered a whole bunch of burned wires in the wiring bundle that contained the alternator wire. The next approach he tried was to run two small wires in parallel. That might have worked if he had insured that the connections at both ends were both solid and low resistance.
His third and final solution was what should have been the first one: install a proper-sized wire.
Unfortunately, he left those burned wires hidden in the wiring bundle for me to find and repair.
bob
s/v Eolian
Seattle
I really liked the post you wrote in your blog about how the first solution you come up with is never the best one.
“non-functioning solar system”
That sounds scary.
LOL. You’re right! 🙂
Blue Sea Systems resettable fuse?
Resettable?
No, it is a normal fuse.
Moral of the story- bring extras of everything! Make sure you have the right extras and when you upgrade make sure all parts are compatible? Also learned some electrical theory which I know nothing about, so much to learn! Thank god I love reading and learning!
Glad you enjoyed it, Patrick.
Hi Mike,
I’m almost caught up in the blog. Being a mechanic , I’d like to suggest instead of another 15 amp fuse, you might try a 15 amp breaker ( they fit into the same holder) That way , instead of burning a fuse the breaker simply opens, then when it cools down, resets its self. I have used these many times in my trade where we find a glitch that “pops” a fuse but we can’t find the problem. It/ they are a lot cheaper than a new controller.
Regards
Dan
I have yet to see anything like that which will fit in the same holder. Then again, I have been searching in every chandlery from Grenada to Trini and I can’t even find the fuses. It was suggested today that I try an auto parts store.
That’s where you’ll find them, if you can’t… Let me know and I’ send you some. When I say fit in to the holder, I mean they are the “spade type”. You won’t be able to close the lid but that’s why I sent the ps about the liquid rubber. You simply coat all the exposed areas…
Got it. Thanks.
P.S. There is. Also a product known as ” liquid rubber” that can solve a lot of problems on any harsh enviroment .
As in anti corrosion?
Yes… We use it to replace worn or cut away wire coatings to seal them up again… Works great, I know because I use it salters and plow trucks, working for the city of TO. Oh yes , it’s available in different colours.
I wonder what they use on the salters and plow trucks down here. 😉