SERVICE and START batteries - and one solar panel...

[antaris]

Hello all,

On my boat I have the typical 1-2-BOTH selector that switches between the SERVICE and START batteries (the SERVICE is a set of 2 batteries in parallel, to be precise).

I also have a flexible 7W solar panel that I connect manually to either of the batteries. I was thinking of permanently installing the set (panel, control box, lcd screen) as well as a 1-2 Switch (much like the 1-2-BOTH selector) so that I can switch the charging from one set to the other.

The main reason is that all batteries are located under the berths and are a tad difficult to access / ease of use in general. Is that a silly idea? I understand that I should never go via BOTH, since that would short-cirquit the two sets.

Any ideas appreciated...

PS> While we're at it, it is ok to switch from 1 to 2 (SERVICE to START) while the engine is running, isn't it (via OFF or BOTH)?

 

[pvb]

PS> While we're at it, it is ok to switch from 1 to 2 (SERVICE to START) while the engine is running, isn't it (via OFF or BOTH)?

Depends how it's wired, but the general rule with these ridiculous 1-2-Both switches is that you never select OFF whilst the engine is running, as it may damage the alternator.

 

[vyv_cox]

You can purchase a controller that will send current from a solar panel to whichever battery needs it, usually with the domestic bank as a priority. Mine was quite expensive with full display of voltages at each battery and current in http://www.sunworks.co.uk/ but Maplins do a basic one very much more cheaply, without the displays.

However, a 7 watt panel does not need a controller and will do very little for a multi-battery installation that from your description has at least three separate batteries. My original arrangement with the controller described above had a 38 watt panel that did not do much for 3 x 110 Ah batteries.

You should not go via OFF. This sends a big spike through the alternator diodes, that can fry them.

 

[antaris]

Many thanks for the replies... I am trying to make-do with the bits I've got... so the controller (albeit very useful) is off my chart for now...

 

[ghostlymoron]

A 7w panel is not going to do much on the battery capacity you have regardless of how its connected. So I would have it permanently connected to the house batteries and leave the engine battery ot look after itself. It should be kept up to snuff by the small amount of engine running after starting.
I personally don't like the 1-2-both-off switches as it's very easy to leave them in the wrong position and flatten your engine battery as well as the possibility of damaging your alternator.
I prefer having an automatic VSR and seperate switches for each battery bank.

 

[vyv_cox]

I have always had 1-2-both switches, so something like 25 years now, and never suffered a flat battery. I tend to leave the switch on the domestic bank (2) more or less permanently, starting the engine on that setting, just occasionally going to setting 1 to check that all is well. I will then charge it for half an hour or so, then switch back to 2. Doesn't seem very arduous or ridiculous to me.

 

[sukris]

I've used this regulator from Maplins:

http://www.maplin.co.uk/dual-16a-solar-charge-regulator-266145 (currently £21.99 - excuse the pun). It uses a common negative, so I used a three-core wire to connect the batteries, which simplifies the wiring. I leave a 10-watt solar panel permanently connected to trickle charge both batteries, which it seems to do quite nicely.

All best,

Chris

 

[antaris]

Cheers guys,

I've got one of these regulators:
here
and a nice display for it here

and (from what I can tell) it only charges 1 battery. Therefore the idea of manually connecting 2 batteries to this regulator via an extra leftover 1-2-BOTH switch...

An alternative would be to buy a new regulator, I guess. Although for 7W I wouldn't wanna spend too much - and will all be compatible (stress, stress!!!).

[All these bits came with my new-old boat, in case you're wondering why I am mixing things up!]

 

[yoda]

The answer is that your proposed setup will work quite happily, the switch just does your job of moving the positive lead from one battery to another and leaves the original boat set up just as it was. The controllers that have 2 outputs are not that expensive so why not put one on your birthday list!

Yoda

 

[VicS]

Make you extra selector switch a simple spdp (+ off ??) switch .. NOT one that can be set to "both" or you risk putting large currents through it and its wiring esp if you start the engine while set to both. Fuse the connections at the battery though.

If the switch has an off position check your solar controller instructions. Some require the battery connection to be made ( to determine the battery volts) before connecting the solar panel

You don't need a fancy regulator with such a small solar panel unless you have very small batteries. I settle for the inexpensive Kemo dual output controller from Maplin.

 

[Sandyman]

Hardly seems worth going to all the trouble of mounting a large 1-2-both-off switch to carry such small currents as you will get from such a small Solar panel when all you need is a small 3 pole switch ............batt 1- off - batt 2 .......common Neg.....
not forgetting a fuse and the KISS principle

 

[misterg]

I also have a flexible 7W solar panel that I connect manually to either of the batteries.
...

Any ideas appreciated...

For a panel that size, you can just use a couple of diodes to "charge" both banks at the same time. (It might be enough to stop the batteries self-discharging, but won't do much else!)

Solar panel (+)
v
v
---->[ D1 |]---->[FUSE1]--->[Battery bank 1]
v
v
---->[ D2 |]---->[FUSE2]--->[Battery bank 2]

Fuses should be as close to the battery bank as posssible; D1 an D2 could be pretty much any 1A+ rectifier diode - 1N4001, etc. (Or you could use Schottky diodes to help eke out the most you can from the panel (e.g. 1N5819), although the difference will probably be negigible.)

 

[Kelpie]

I installed a 10w panel last year. Just wired it straight to the house battery (100Ah). There's a fuse in there, but that's about it. It helps top up the battery but it's really not a significant amount of power.
I've been checking it over the winter and it's not even keeping up with self-discharge of the battery... but then again the OP is a bit closer to the equator than I am.

 

[Bilgediver]

xx

 

[William_H]

For a panel that size, you can just use a couple of diodes to "charge" both banks at the same time. (It might be enough to stop the batteries self-discharging, but won't do much else!)

Solar panel (+)
v
v
---->[ D1 |]---->[FUSE1]--->[Battery bank 1]
v
v
---->[ D2 |]---->[FUSE2]--->[Battery bank 2]

Fuses should be as close to the battery bank as posssible; D1 an D2 could be pretty much any 1A+ rectifier diode - 1N4001, etc. (Or you could use Schottky diodes to help eke out the most you can from the panel (e.g. 1N5819), although the difference will probably be negigible.)

I agree with Misterg completely. However if you have a panel with a small box that holds terminals and a diode then you need only one more diode. Try to get the same kind of diode that is on the panel. So the anode of the new diode connects to the panel itself. ie to the diode of the existing diode. Run another wire from the cathode of the new diode to a battery pos. Use the old wire pos to go to the other battery. neg wire to both batteries. Fit fuses at battery ends.
The cathode of a diode is the point of the arrow or the band end. This arrangement will ensure that both batteries are charged to an equal voltage (so more current to bigger battery). By using the existing diode you do not lose any extra voltage. Not that that makes much difference considering you will be starting with near 20v from panel no load.
if you can't find or get to internal panel diode do as Misterg says. Certainly no need for a controller/regulator. good luck olewill

 

[antaris]

Many thanks for all the replies.

I guess that I'll just be connecting it straight to the service battery - since I am now convinced that the 7W is really not worth the extra hassle.

As for the more technical answers (Misterg), many thanks, but I am afraid that I am not that technically savvy - even so the answer may assist someone else! I would try to understand if my system was more than 7W (and therefore worth the mind-bending!!!).

cheers all

 

[geem]

I refreshing to find somebody with the same view as mine on battery management. I had this set up on my last boat and the one before. Never caused me any problems in 20 years. Domestic bank does everything. 'Engine battery' is just an emergency backup if domestic bank went flat which it never has in 20 years!
New boat has split charge diodes and some very elaborate wiring that I am slowly working my way through to simplify.