Charging batteries

[eddystone]

Before failing to start my engine yesterday, I checked all three (identical) batteries and they were showing about 12.3V (a bit low but enough to start I would have thought - not that I think that was the problem as it turned over all right). I would have expected the designated engine battery to be separate and the 2 domestic batteries to be in series, but it seems all three are connected together. I was wondering about charging them up with a portable charger - do I have to do all separately or can charge flow from one to another?

To avoid unnecessarily clogging up the forum, I wonder if there are any particularly recommended books on boat maintenance, preferably written for idiots (or at least clumsy duffers). Also something up to date on boat electrics/electronics for dummies, just enough to diagnose problems and enable me to fit chart plotter, AIS and navtext and associated aerials. (you may conclude that with the level of knowledge displayed in the first sentence I shouldn't try but I feel I need to have a go)

 

[GrahamM376]

Calder's "Boatowner's Mechanical and Electrical Manual" is pretty good and this thread has suggestions - http://www.ybw.com/forums/showthread.php?285281-Which-boat-electrics-book

 

[Storyline]

I can wholeheartedly recommend Electrics Afloat - AE Garrod. Superb graphical illustrations and easy to understand.
http://www.amazon.co.uk/Practical-B...1660&sr=8-54&keywords=marine+electrical+books

 

[vyv_cox]

Before failing to start my engine yesterday, I checked all three (identical) batteries and they were showing about 12.3V (a bit low but enough to start I would have thought - not that I think that was the problem as it turned over all right). I would have expected the designated engine battery to be separate and the 2 domestic batteries to be in series, but it seems all three are connected together. I was wondering about charging them up with a portable charger - do I have to do all separately or can charge flow from one to another?

Having all three connected in parallel permanently seems to defeat the object of having separate domestic and starter batteries. A 1-2-both-off switch is the simple answer to keeping them separate. You can charge all three batteries with one charger, again, provided they are connected together in parallel. However, a typical portable trickle charger does not deliver a high current and the charging will be very slow.

 

[RAI]

Charge the starter battery enough to start the engine and then use the engine to charge all of them.

 

[Caer Urfa]

Before failing to start my engine yesterday, I checked all three (identical) batteries and they were showing about 12.3V (a bit low but enough to start I would have thought - not that I think that was the problem as it turned over all right). I would have expected the designated engine battery to be separate and the 2 domestic batteries to be in series, but it seems all three are connected together. I was wondering about charging them up with a portable charger - do I have to do all separately or can charge flow from one to another?

To avoid unnecessarily clogging up the forum, I wonder if there are any particularly recommended books on boat maintenance, preferably written for idiots (or at least clumsy duffers). Also something up to date on boat electrics/electronics for dummies, just enough to diagnose problems and enable me to fit chart plotter, AIS and navtext and associated aerials. (you may conclude that with the level of knowledge displayed in the first sentence I shouldn't try but I feel I need to have a go)

I agree with vyv Cox and split the batteries up using the best one for 'engine starting only'.

I also suggest getting a good 'smart' marine battery charger such as one of the C-Tec range, I bought this MXS 5 Model earlier this year and its great, plus you can easily swop the leads over to charge other battries.

http://www.ebay.co.uk/itm/CTEK-Mult...48&rk=1&rkt=5&sd=121209552467&#ht_2205wt_1188

Mike

 

[Spi D]

Depends on your setup. As so often, it comes down to budget and requirements compromises.

Charging by running the engine can't bring a battery from flat to 100% - regardless of running hours. The regulator will sense 'enough' volt long before the capacity (Ah) is 100% and simply cut charging.
If wanting to combine banks while running the engine for common charging and then separate them when engine is off, smart devices like the Septor will do the trick.

Ideally you want to separate engine and domestic battery banks (where a bank may consist of more identical batteries) and then to charge the banks separately. Intelligent chargers will help the batteries in more ways to give you shorter charging times, more power on tap and extend battery service life. Battery banks' size (Amp capacity) should be determined by calculation of total consumption.
Separation of banks can be manual (switch) or automated.

Due to different design, batteries made for domestic / starting are best at their intended uses, but dual type are available. Note, that multi bank chargers commonly do not accept banks to be of mixed types (AGM, Gel, flooded).

 

[eddystone]

Having all three connected in parallel permanently seems to defeat the object of having separate domestic and starter batteries. A 1-2-both-off switch is the simple answer to keeping them separate. You can charge all three batteries with one charger, again, provided they are connected together in parallel. However, a typical portable trickle charger does not deliver a high current and the charging will be very slow.

I do have a 1-2-both off switch so maybe I need to look a bit harder at the wiring, but I was sure the one I thought was the engine battery had it's negative terminal wired to one of the other two - obviously I need to determine for sure which is the engine battery! The charger I found on the boat is a Halfords Automatic battery charger (is that a trickle charger?). I was thinking of replacing that with a combined charger/jump start thing but not sure how many amps needed to jump start an 18HP 2cyl diesel.

 

[RAI]

I do have a 1-2-both off switch so maybe I need to look a bit harder at the wiring, but I was sure the one I thought was the engine battery had it's negative terminal wired to one of the other two - obviously I need to determine for sure which is the engine battery! The charger I found on the boat is a Halfords Automatic battery charger (is that a trickle charger?). I was thinking of replacing that with a combined charger/jump start thing but not sure how many amps needed to jump start an 18HP 2cyl diesel.

Your batteries would have a common negative/earth wiring, its the positive/live that goes through your switch. Both the chargers are essentially trickle chargers. The jump starter will do the trick if the engine starts easily, but maybe not repeatedly between charges.

 

[eddystone]

Your batteries would have a common negative/earth wiring, its the positive/live that goes through your switch. Both the chargers are essentially trickle chargers. The jump starter will do the trick if the engine starts easily, but maybe not repeatedly between charges.

Got it, thanks

 

[Bodach na mara]

Your batteries would have a common negative/earth wiring, its the positive/live that goes through your switch.

Not necessarily, there are many weird and wonderful connections found in boat electrical systems. In mine, the positive from the alternator goes to a diode splitter and the two outputs from that go to the engine and domestic batteries. The negative terminals of the batteries are permanently linked and are connected to earth via a switch. The batteries are independent and the engine starter battery cannot be discharged by overuse of the domestic system. This system has the advantage that, if the engine batteries are not up to the job of starting the engine in cold weather, it is only necessary to connect a single jump lead between the positive terminals to get the higher current needed.

To answer the OPs question about failure to start the engine, a low battery bank may not be able to supply the high current required, although I would have expected three in parallel to be able to do this.