Battery charging

[coliholic]

On my motor boat I have two separate banks of batteries. One single 135AH battery is recharged by the port engine and supplies just power for starting to that engine. Two 135AH batteries are connected in parrallel and are charged by the starboard engine and provide starting power to the stbd engine and domestic services.

I've always kept the batteries topped up by connecting to a normal car type charger running off shore power but this is a bit of a performance, opening the engine compartment, taking off the lid of the battery box, connecting the charger via crocodile clips and plugging in to a 13Amp socket, then a couple of days later having to go back on board to change the connections to the other battery.

So, I've come up with a cunning plan. I'm planning to connect a two way change over switch in the red lead from the charger and mount that switch remotely in a locker so I can easily get at it, along with a mains on off switch and an ammeter so I can see what current's being drawn by each battery. I intend to then take an output from this two way switch to each battery and then I can just switch the charger from one battery to the other. Obviously the black lead from the charger goes to all three batteries negative terminals.

Can anyone see any flaws in this?

Any chance of causing electrolysis problems?

I realise that I should really spend £200 or so on a proper Adverc or Sterling charger, but am lookinjg for a slightly less expensive solution since I've already got the battery charger doing nothing anyway.

Any thoughts please?

 

[BarryH]

What sort of charger is it. Most of the cheapy one dont realy give full charge because their not regulated charge wise. So realistically you'll only get about 80% charge. Sounds feasable tho. would it help if you could disconnect the batts totally from the boats circuits to get round the electorolysis thing. Just a thought

 

[coliholic]

It's a quite old, very simple charger. Have opened the case and it's just a transformer and a regulator. Gives 14.4Volts. Not really feasible to disconnect the batteries, since the battery switches are in the engine compartment and if I'm going to switch them off, may as well persevere with the old charging system. Just trying to make things a bit easier without spending a fortune. Never actually had a battery problem before, the engines seem to keep them nicely charged, just thought I'd add the charger for when I'm on shore power. Probably only use it now and again, won't leave it switched on permanently.

 

[yoda]

I can see one small problem I'm afraid. The switch fitted to the two battery positive (red) leads will need to be a break before make switch otherwise when you change over from a fully charged battery to a less charged one they will for a short time be in parrellel and will try to achieve a common level hence sending a large current down some quite small wires. Easy solution is to use a three position switch so you have to go to the off position as you change over. These are easy to get hold of so not a big problem. Any more ? give me a shout.

Yoda

 

[jollyjacktar]

An anti surge diode in the line would possibly do the job of a 'break then make' switch. Do not install an ammeter in the main feed line, starting currents would be excessive. I am always careful not to have too many gadgets in the main suppy line between the batteries and the starter and/or ignition feeds as there may be a need in emergency to have as little voltage drop as possible and as few things to go wrong, just in case.

What you need to monitor is the charge/discharge circuits. Best read up about things. However if the system has been working well all that time, why bother. Generally unless abused, batteries do not just fail instantly, but gradually deteriorate and this progress can be monitored and noted in your log to give you an estimate of the staus of things. A better check may be to monitor the batteries condition etc using volmeters [easier to fit] and hydrometer.

As for charging the circuit the battery, with a bit of understanding of the electrics and some local advice it should be possible to break into the circuit at any place, say at a cigarette lighter socket and plug in your trickle charger there. Better still you can now get self regulating battery chargers [quite cheap, sounds like you need to treat yourself to a new one anyway] that can be left on all the time when attached to main supply.

Happy charges.

 

[terryw]

Colin.

When I had my previous boat I became paranoid about flat batteries after I managed to flatten them both overnight (left the fridge running). The problems I had connecting a charger to the terminals was not one I wanted to repeat too often, so I fitted two pairs of "remote" terminals above the deck (a positive and negative to each battery). Mine were actually the terminal posts you get on Hi-Fi speakers, which are conveniently coloured black and red, and were connected by suitable cable to the relevant battery terminals. When I wanted to charge the batteries I just connected the charger to these for a few hours, and no more lifting of deck panels, and worming into confined spaces. It worked for me, and was very cheap.

Terry

 

[Guest]

Gunson chargers are worth a look - Mine has given good service although I charge only one bank at a time. The charger has a trickle facility(voltage control) to prevent gassing etc. I leave it on a week at a time without problems but I disconnect it when on board so the auxilliaries I use dont overload it. The automatic bilge pump is left connected but draws less than the max recommended by Gunson.

The point of this post is that the charger was less than £40 so it is a cost effective solution to keeping the batteries in good shape.

PZ - ps Gunson have a website for further info!

 

[pandroid]

I'm surprised that you've got away with leaving the things on charge for so long. Most simple car chargers continue to put 14.4 volts into batteries regardless of their state of charge, and end up by gassing away much of the electrolyte. The posher switched mode ones (mastervolt etc) detect this and switch down to 12.5 volts (float mode) to prevent gassing, so they can be left on. I once ruined a 'sealed' battery this way. Dont you have to keep topping the things up?

 

[andyball]

14.4 continuously is probably OK( but 13.8 is better,although that won't charge 'em fully in the first place).....I agree that many cheap chargers overcharge/damage batteries, but that's 'cos they eventually creep up beyond this level.

I have a cheap 4amp charger,even that will eventually put 15+ volts into a 130A/H bank of batteries, although from flat, it takes days.

so: just because you measured 14.4.....don't presume it'll stay at that.

 

[coliholic]

Thanks all for your advice.

Thank to all who bothered to reply. Any other opinions since I'm planning to do this at the weekend?

Will keep the period of on-charge a bit shorter i.e a day or so, and will switch mains off before changing batteries on the two way switch, but anything else I should be aware of?

Oh and yes I do have to top up the water levels in them about once a month.

 

[ParaHandy]

Re: Thanks all for your advice.

Colin

If you have a digital volt meter you ought to check the open-circuit (ie nowt connected to them) voltages of each battery - particularly the pair in parallel just as a precaution in case one of the pair is duff or that they're past their best. There's a good explanation of the relationship between voltage and charge state and much more at:
http://www.geocities.com/bjb_darden/carfaq.htm
Halfords do a decent charger with trickle charge and an accurate dvm meter. Cost for both <£90 total I think.

Douglas

 

[coliholic]

Re: Thanks all for your advice.

Thanks Doug, will check with DVM and take a look at the site.

 

[LadyInBed]

A couple of other thoughts.
- Plug the mains end of the Charger in via a time switch so you can regulate how long the charger is on each day.
- Buy a couple of 'high' current low resistance diodes (ie RS # 357-4100 for < £5) and use them as blocking diodes so you can trickel charge both banks at the same time from one charger.