Solar info required.

Submitted: Saturday, Sep 16, 2017 at 17:26
ThreadID: 135600 Views:2783 Replies:5 FollowUps:9
This Thread has been Archived
Howdy,
Just redoing the electrics in our camper and have a query that I can't find an answer to, any help would be great.

2X135AH deep cycle batteries fitted, Redarc 1240D BCDC charger just installed to camper.

Previously had 2x small cranking batteries on the camper, charged by Redarc 1225LV BCDC under bonnet of vehicle.

Used to plug 200W solar panels into 1225lv under bonnet and charge batteries that way while stationary.

My question is, if I am using a BCDC to actually charge the batteries, do I need 200W solar panels? Couldn't I just use a 50W solar panel to power the BCDC to charge the batteries?

I would like to get rid of the 200W panels as they take up a lot of room and are heavy.

BCDC requires minimum of 9V to operate, would 50W solar panels manage this or am I thinking off the planet?

Regards
Peter
Back Expand Un-Read 0 Moderator

Reply By: IvanTheTerrible - Saturday, Sep 16, 2017 at 17:52

Saturday, Sep 16, 2017 at 17:52
BCDC is useless if you are in one place for several days
AnswerID: 613814

Follow Up By: RMD - Saturday, Sep 16, 2017 at 18:05

Saturday, Sep 16, 2017 at 18:05
Why is it useless if stopped in one place for a few days?

Won't the connected solar charge the batteries?

Just having 50watts of solar won't do much though. If batteries need to be charged in a reasonable time, the 200w is needed.

I don't like the idea of the DC DC unit having been under the bonnet where engine heats it so it becomes fairly useless because of radiant heat.
0
FollowupID: 884346

Follow Up By: TTTSA - Saturday, Sep 16, 2017 at 18:07

Saturday, Sep 16, 2017 at 18:07
Why is that?

I am wanting to power the BCDC from the solar panel, hence my question is will a 50W solar panel supply at least 9V to the BCDC to charge the batteries?
0
FollowupID: 884347

Follow Up By: TTTSA - Saturday, Sep 16, 2017 at 18:16

Saturday, Sep 16, 2017 at 18:16
RMD, the "why is that" was directed at Ivan. Your followup wasn't there when i replied.

DC DC unit performed great under the bonnet, it matters where you put it.

Now have the larger unit on the camper so that doesn't matter.

Regarding the 50W panel, If I only need 9V to power the DC DC, which is actually charging the batteries and not the panels, wont the 50W panel do that? Or is there something I am missing here.

Peter
0
FollowupID: 884348

Follow Up By: Bob Y. - Qld - Saturday, Sep 16, 2017 at 18:43

Saturday, Sep 16, 2017 at 18:43
No free lunch here, Peter. The Redarc might only need 9v to start working, but you need "bulk" to actually charge your 2 batteries. I'd stick with the 200w panel, or if money is not too tight, get some flexible panels which are much lighter. 50w panels would be flat out keeping one battery charged.

I've got a 200w panel on roof of my canopy, with 2 x 120amphr batteries, and sometimes the batteries are struggling to keep up with the load overnight.

Bob

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 884349

Follow Up By: TTTSA - Saturday, Sep 16, 2017 at 18:52

Saturday, Sep 16, 2017 at 18:52
Thanks Bob,

We are looking at the options of solar mat type panels, just thought there might be a free lunch around the place.

Cheers
1
FollowupID: 884351

Reply By: RMD - Saturday, Sep 16, 2017 at 20:45

Saturday, Sep 16, 2017 at 20:45
TTTSA
The voltage to switch something ON has nothing to do with the current flow intensity you need to charge big batteries which are partially discharged. You can pee into a bucket and repeated attempts will fill the bucket, but if you wish to fill the bucket with, electrons in this instance, you need a large flow, ie, more watts at a higher voltage to do the charge in a relatively short time. 1/4 of 200 watts mean at least 4 times longer to charge the batteries. Since the sun doesn't shine at night, eventually, later in the month, your batteries may achieve full charge, IF you don't use any of the stored charge. 50 watts will not cut the mustard.
AnswerID: 613819

Reply By: Allan B (Sunshine Coast) - Saturday, Sep 16, 2017 at 22:45

Saturday, Sep 16, 2017 at 22:45
.
The Redarc specification that their BCDC chargers will operate "down to 9v input" needs to be fully understood.

The purpose of the charger is to overcome the voltage drop in the cabling from the point of supply which is the terminals of the cranking battery.

Due to volt-drop in the cabling, the voltage input at the charger may fall well below the cranking battery terminal voltage and the charger will continue to properly operate with an input as low as 9 volts. However, the charger needs to determine if the voltage at the cranking battery is at least 12.7v (typically). It does this by briefly pausing the charging every 100 seconds. When paused there is no current to cause cable volt-drop so the charger is now looking at the true voltage at the cranking battery terminals. If it is greater than 12.7v charging continues but if less then charging is suspended. The charger will not operate from a supply source (such as solar) less than 12.7 volts.

In this way the charger is prevented from drawing current from the terminals of the cranking battery below nominally 12.7v. Note that this voltage setting varies slightly with the charger model and that the "-IGN" models also shut down when the ignition circuit is off.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

AnswerID: 613821

Follow Up By: RMD - Sunday, Sep 17, 2017 at 10:36

Sunday, Sep 17, 2017 at 10:36
Allan
If solar is used, won't the BCDC unit still charge the aux battery irrespective of the vehicle start battery voltage?
TTTSA said he used the solar to charge the batteries previously.

I was confused as to what he meant by cutting 200w solar down to 50w solar and still expecting the 50 w to do similar work in similar time.
0
FollowupID: 884365

Follow Up By: TTTSA - Sunday, Sep 17, 2017 at 12:27

Sunday, Sep 17, 2017 at 12:27
Hi RMD

I was hoping to be able to use 50W panel to power the charger, I wasn't sure if it made any difference using 50W or 200W to satisfy the charger and still get the same output from the charger.

Wishful thinking it seems.

Thanks
0
FollowupID: 884368

Follow Up By: Allan B (Sunshine Coast) - Sunday, Sep 17, 2017 at 12:39

Sunday, Sep 17, 2017 at 12:39
RMD,
The solar will continue to feed via the BCDC only so long as the unladen solar voltage stays above 12.7 volts. Should that voltage fall below 12.7 the BCDC will cut out until it rises to above 13.2 volts. (These voltages are typical and vary by model)

As to the 200W/50W confusion, I think TTTSA has now realised his error.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 884369

Reply By: Sigmund - Sunday, Sep 17, 2017 at 04:24

Sunday, Sep 17, 2017 at 04:24
You need to do a power budget - amps withdrawn v watts deposited. Say if you typically camp for 3 days and start fully charged.

If you don't want to do that fit 250w of solar panels for every 100 ah of storage according to Collyn Rivers. See how that works.
AnswerID: 613822

Reply By: TTTSA - Sunday, Sep 17, 2017 at 09:55

Sunday, Sep 17, 2017 at 09:55
Thanks for the helpful replies fellas, getting the gist of it now. Think i'll keep looking at the blanket type panels to save on weight and storage space.

Cheers
Peter
AnswerID: 613829

Follow Up By: Sigmund - Sunday, Sep 17, 2017 at 11:26

Sunday, Sep 17, 2017 at 11:26
Way to go.
Just beware of the cheapies. Get reliable data on their output before stumping up.
1
FollowupID: 884367

Sponsored Links