Battery management/charging advise..

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wipe_out

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Will be moving the boat to a swing mooring shortly so no more shore power to keep the batteries charged.. The boat has two 85ah batteries and a 1-2-both-off switch..

Looking at 10w solar charger kits with a charge controllers and these seem reasonable to keep the batteries topped up.. Nothing running while I'm away other than the GSM alarm system I am going to install so requirements aren't high..

The question is how to manage charging both batteries.. If I connect to both directly I would effectively be bypassing the main battery switch.. I don't want to use diodes because of the voltage drops associated with them.. I don't want to connect to a single battery and leave the switch on "both" because if there is a problem both batteries would drain..

Have thought about a voltage sensitive relay but if I went that way I would probably get a big one and wire that in as the standard charging mechanism from the alternator as well and have effectively an engine battery and domestic battery but that isn't really what I had in mind at this stage..

How do you manage charging two battery banks independently with solar panels?
 
wipe_out said:
How do you manage charging two battery banks independently with solar panels?
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Buy a dual battery charger. I'm just about to fit one of these

1369313115_74774200.png


which is about £35. For another £35 I have added one of these

1343569962_45744000.png


which lets me monitor and control everything remotely. You can tell the controller what type of batteries you have, which one you want charged first and it does the rest. I haven't tried it yet, as connection day is next week sometime, but the reviews seem OK. Photonic Universe seem to be the main importers, but they are available unbranded from other companies. Worth checking prices direct, though ebay and through amazon as well as directly. The remote meters seem to be in rather short supply at the moment.
 
wipe_out said:
Will be moving the boat to a swing mooring shortly so no more shore power to keep the batteries charged.. The boat has two 85ah batteries and a 1-2-both-off switch..

Looking at 10w solar charger kits with a charge controllers and these seem reasonable to keep the batteries topped up.. Nothing running while I'm away other than the GSM alarm system I am going to install so requirements aren't high..

The question is how to manage charging both batteries.. If I connect to both directly I would effectively be bypassing the main battery switch.. I don't want to use diodes because of the voltage drops associated with them.. I don't want to connect to a single battery and leave the switch on "both" because if there is a problem both batteries would drain..

Have thought about a voltage sensitive relay but if I went that way I would probably get a big one and wire that in as the standard charging mechanism from the alternator as well and have effectively an engine battery and domestic battery but that isn't really what I had in mind at this stage..

How do you manage charging two battery banks independently with solar panels?
Click to expand...

If KISS is your moto fit two 5 watt solar panels . One connected to each battery.
With a ratio of 5 watts to 85 Ah regulators are not needed

Alternatively a 10 watt panel and two diodes. No regulator necessary. Voltage output from solar panels is so high that the volts drop across the diodes is not important. Can minimise it anyway by using Schottky diodes
 
JumbleDuck said:
All very well and simple, but means that half the solar output goes to charging the engine battery, which almost certainly doesn't need it.
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He only needs to keep them charged but could use a 2.5w panel on the starting bat and a larger one on the other if there was a chance it wasn't going to charge up between visits.
 
ianj99 said:
He only needs to keep them charged but could use a 2.5w panel on the starting bat and a larger one on the other if there was a chance it wasn't going to charge up between visits.
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To be honest, I can't see a huge point in solar charging the engine battery ... and yes, I know I've bought a dual battery charger, but that's mainly so I can use its remote display to monitor both batteries. The charge needed to start the engine (200A for 5 seconds?) will be replaced in next to no time and self-discharge is very low. I have a couple of classic cars in storage which get started perhaps four times a year, and their batteries cope perfectly well.
 
VicS said:
Alternatively a 10 watt panel and two diodes. No regulator necessary. Voltage output from solar panels is so high that the volts drop across the diodes is not important. Can minimise it anyway by using Schottky diodes
Click to expand...

+1
2 diodes mounted near the battery +ves or if you can get into the solar panel connection box add another diode and use existing diode but do fit a fuse at each battery +ve
no need for a controller/regulator. good luck olewill
 
Lots of good advice as to what to do about charging. Out of interest, why are you going to bother to run the gas alarm 24/7? We just turn the gas bottle off when we leave the boat. The gas bottle stowage drains overboard so there's no danger of gas getting into the boat while we are away.
 
john_morris_uk said:
Lots of good advice as to what to do about charging. Out of interest, why are you going to bother to run the gas alarm 24/7? We just turn the gas bottle off when we leave the boat. The gas bottle stowage drains overboard so there's no danger of gas getting into the boat while we are away.
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Will be running a GSM alarm not a gas alarm.. :)

GSM alarm will monitor bilge water level and if anyone accesses the boat.. It will then send me a text message..
 
GHA said:
You need to be a bit careful with no regulator , even with a small panel, in the rare event of a few days of sun....

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Yes, this is what I had read which is why for the cost of a charge controller I would rather know the batteries are being managed properly..

Anyone know if a single solar panel be connected to two charge controllers?
 
wipe_out said:
Yes, was more a theoretical question in the case of 3 or 4 battery banks being able to share the capacity of the solar panels.. Not really relevant to my original question.. :)
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Well, physically you could connect one solar cell to more than one regulator, but I'm not sure what the effects would be. Possibly bizarrely interesting as the two regulator confused the hell out of each other with voltage drops at the cell. It's probably worth doing the experiment!
 
wipe_out said:
Will be moving the boat to a swing mooring shortly so no more shore power to keep the batteries charged.. The boat has two 85ah batteries and a 1-2-both-off switch..
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How often do you use the boat?

I am on a swing mooring and decided to remove the wind generator last winter as it was about as old as me and not generating much, if any, power.

So my plan is to carefully monitor the battery voltage this summer to see if I need anything in addition to the engine for my power needs.

I have two 85AH batteries rigged in parallel giving me 170AH and am measuring the voltage when I arrive and leave the boat, but my power use is minimal. VHF, a car radio, nav lights, depth and wind instruments and a little used autohelm (working on a boom to tiller self steering set up to remove the autohelm as much as possible). So far I am finding that with an hours engine use, in other words, out of the river I am fully charged.
 
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