10W solar panel on a 50Ah cranking battery Regulator needed?

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Avocet

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Hi All,

"Asking for a friend"... (no, really)!

He has a 50Ah cranking battery and a 110 Ah leisure battery. He was going to get a couple of 10W solar panels and leave one connected to each battery over the winter to keep them topped up. I think the leisure battery will be fine with that, but was wondering about the smaller cranking battery. Would that be OK with a 10W panel permanently connected, or does he need a regulator too?
 
Avocet said:
Hi All,

"Asking for a friend"... (no, really)!

He has a 50Ah cranking battery and a 110 Ah leisure battery. He was going to get a couple of 10W solar panels and leave one connected to each battery over the winter to keep them topped up. I think the leisure battery will be fine with that, but was wondering about the smaller cranking battery. Would that be OK with a 10W panel permanently connected, or does he need a regulator too?
Click to expand...
There are a couple of "rules of thumb" regarding this.

If the size of the panel , in watts, exceeds 10% of the battery capacity, in Ah, a regulator is required.​
​
Panels over 10 watts should always have a regulator.​

On this basis the 50 Ah battery/10 watt panel combination should have a regulator but in wintertime probably not necessary.
I have found that a 5 watt panel will easily keep a small battery charged without needing a regulator.
 
Avocet said:
Hi All,

"Asking for a friend"... (no, really)!
Click to expand...
This sentence, or one like it, is posted every so often, or at least occasionally :)

Why do people ask a mate to pose the question on their behalf. Joining YBW is free, its easy to join, unless you are banned. The forum benefits from a varied membership and depends on people, with diverse views, to contribute. If you run a commercial activity in conflict with Forum rules - you need to be discrete.

So....why?

Jonathan
 
A 10W panel will produce a maximum of about 5Ah per day in summer. Halve this for less winter daylight hours and halve again for less sunshine and reduce again for imperfect orientation. This will bring it down to less than 1Ah per day which is an average of about 40mA. A Victron MPPT controller draws about 25mA and will waste most of the output although a simple PWM controller will used less standby current.
You will be fine on the smaller battery in winter with a direct (fused) connection. Just check the voltage regularly especially on a sunny day and ensure it is not much above 14V. When I did this with a 30W panel feeding 2 x 100Ah batteries I found the batteries sat at about 13.6V throughout the winter. If you find the voltage starts to get too high you can always change the orientation of the panel to a less favourable direction. (I split the charge with Schottky diodes so I didn't have to directly parallel the two batteries and the lowest battery would take most of the charge.
 
Neeves said:
Why do people ask a mate to pose the question on their behalf. Joining YBW is free, its easy to join, unless you are banned. The forum benefits from a varied membership and depends on people, with diverse views, to contribute. If you run a commercial activity in conflict with Forum rules - you need to be discrete.

So....why?
Click to expand...
I can think of 101 reasons. Perhaps this is not on a boat would be the first.

I have friends who don't do forums and some who don't do the internet!
 
Neeves said:
Why do people ask a mate to pose the question on their behalf.
Click to expand...
I think you may have taken "asking for a friend" too literally. The friend may not even have asked for an opinion, or asked the OP id *he* has an opinion. That is not that same as saying "can you go on YBW and find out...". That said I'm not surprised if people can't be bothered signing up for a one-off question, especially if they don't really like using computers.
 
andsarkit said:
Just check the voltage regularly especially on a sunny day and ensure it is not much above 14V.
Click to expand...
andsarkit said:
If you find the voltage starts to get too high you can always change the orientation of the panel to a less favourable direction.
Click to expand...
You are assuming that the owner is close to the boat to be able to time his visits when the weather is good to check the voltage and move panels. For a winter "trickle charge" installation I would this it is likely that he is leaving the boat unattended for weeks on end.
 
Its fine ... I have 10W panel on my small Mobo - maintains a Lead Acid battery of 80Ahr without regulator. Before I changed the battery - I had a 7Ahr SLA Alarm battery charged by that panel - without regulator.
What killed the SLA was not the panel - but the lack of charge to it when boat went into barn and I forgot to remove the battery and put on the bench.

Reminds me - I forgot to sort the 80Ahr battery when I put boat in barn this time !!

The 10W panel will be lucky to get anywhere near half that in winter ... probably less than a quarter ...
 
Neeves said:
This sentence, or one like it, is posted every so often, or at least occasionally :)

Why do people ask a mate to pose the question on their behalf. Joining YBW is free, its easy to join, unless you are banned. The forum benefits from a varied membership and depends on people, with diverse views, to contribute. If you run a commercial activity in conflict with Forum rules - you need to be discrete.

So....why?

Jonathan
Click to expand...

I'm trying to persuade him to join. Lots of people are a bit shy about asking technical questions, if they're not that technical themselves. Me... I'm more brazen, so I don't mind! I know some technical "stuff" but enough to know that there are things I don't know. Nothing more sinister than that!
 
Sandy said:
I can think of 101 reasons. Perhaps this is not on a boat would be the first.

I have friends who don't do forums and some who don't do the internet!
Click to expand...

Definitely a boat (Halcyon 27). We're practically brothers, because Avocet is a Cutlass 27... 😉
 
andsarkit said:
A 10W panel will produce a maximum of about 5Ah per day in summer. Halve this for less winter daylight hours and halve again for less sunshine and reduce again for imperfect orientation. This will bring it down to less than 1Ah per day which is an average of about 40mA. A Victron MPPT controller draws about 25mA and will waste most of the output although a simple PWM controller will used less standby current.
You will be fine on the smaller battery in winter with a direct (fused) connection. Just check the voltage regularly especially on a sunny day and ensure it is not much above 14V. When I did this with a 30W panel feeding 2 x 100Ah batteries I found the batteries sat at about 13.6V throughout the winter. If you find the voltage starts to get too high you can always change the orientation of the panel to a less favourable direction. (I split the charge with Schottky diodes so I didn't have to directly parallel the two batteries and the lowest battery would take most of the charge.
Click to expand...

Thanks for that. Could I ask what size fuse you'd recommend, please? (That's a question from me, really - Avocet has a 100 Ah leisure battery permanently connected to a 10W panel, but I hadn't thought to put a fuse in the line!
 
Avocet said:
Thanks for that. Could I ask what size fuse you'd recommend, please? (That's a question from me, really - Avocet has a 100 Ah leisure battery permanently connected to a 10W panel, but I hadn't thought to put a fuse in the line!
Click to expand...

Think about the wattage and amps liable to be from the panel ... people are going to start on about Ah etc .. etc ... but at end of day that panel will not approach 1A ....

I have various trickle charger solar panels for use on cars / caravans etc .. and near all are 5 to 10W panels with 5A fuses ... I would assume Slow Blow to avoid blowing with any 'spike' when panel first connected ..
 
Refueler said:
Think about the wattage and amps liable to be from the panel ... people are going to start on about Ah etc .. etc ... but at end of day that panel will not approach 1A ....

I have various trickle charger solar panels for use on cars / caravans etc .. and near all are 5 to 10W panels with 5A fuses ... I would assume Slow Blow to avoid blowing with any 'spike' when panel first connected ..
Click to expand...
I'd agree with 5a fuses, as long as the wiring is rated to at least 5a. They are there to protect the cable, so no point messing about fitting a million different sizes fuses to the same size cables. Automotive blade fuses are a good choice.
 
I wouldn't trust the cheap charge controllers, a couple of have failed on our greenhouse system.

Some batteries don't seem to need much float charging over winter, others do, more so as they get old.
No substitute for visiting the boat at least every few weeks and checking things over.
 
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