another battery charging question

[catalac08]

I have currently 2x85AH leisure batteries with a changeover switch and use either for starting 30hp main outboard engine. Am continuously challenged for power on longer/night trips but even in daylight the 70W (max) output generator only contributes say 3/4A at cruising revs and with instruments/radio/vhf I am often running at a modest charge deficit even when motoring and a substantial deficit sailing.
A new wind generator will help keep the batteries topped up, supplimented by a generator when well away from other boats.
I want to get another battery to have more storage capability and my inclination is to get another dedicated starting battery and double up the two leisure batteries in parallel but will this give the alternator or wind generator any problems i.e trying to charge a 170AH battery bank.. I appreciate it is not ideal having batteries connected like this but my whole set up is not ideal and I just have to do the best I can at a low level of cost

any thoughts on this arrangement - better battery configurations or something radical to do with charging on boats?

 

[Talbot]

Had the same problem but then fitted a 180watt solar panel! my domestic is 200 amp/hr.

just need to ensure that regulator allows charge to two banks, preferably on a priority basis.

 

[john_morris_uk]

It won't give the charger any problems, but obviously won't solve your charge-discharge equation problem either.

Hopefully the wind generator will balance the equation out in the right direction and the extra capacity won't just delay the moment that you realise that your batteries are dead!

 

[VicS]

Your problem is really the lack of output from your alternator. Within reason increasing the total capacity of the batteries will cause no problem but at the end of the day if you use more power than you can generate doing so will not help.

Solar panels and/or wind generators are possible ways of increasing your power generation capabilities as is your generator.

Is a larger alternator for your engine an option? At 30 hp you would seem to have adequate power available. I think your present alternator would be appropriate for charging a 60-80 ah battery, maybe a bit more, but 170 ah and more may be getting beyond a reasonable capacity to charge with that alternator.

 

[pappaecho]

I have a 40amp alternator and a Rutland 913 wind charger with Rutland dual bank charging system. I have about 150 amp engine bank and 200 amp deep discharge service bank.
The biggest discharge is the Peltier fridge, which will reduce the service bank to about 9.5 volts after a couple of days continual use, without input from either the engine or the Rutland.
It adequate wind, 10 knots and above, the wind generator, automatically charges the bank with the lowest voltage, which is inevitably the service bank, and when fully charged will stop the turbine, in strong winds for example. I have not seen either bank drop below 12.3 volts this year with full use of fridge, autohelm, lights and sundry electronics. My boat is on a swinging mooring, so there is no outside power inputs.
If the wind turbine is actively charging, and the engine started, the system feathers the wind turbine, as the input from the alternator is above the cutoff voltage. Whilst the alternator proably could be increased to 60-70 amps, in my view to little purpose, because the numbers of hours per week for the engine running is only about 1 hour. The wind turbine is probably running 18 hours per day, putting something back into the battery banks, so that the net weekly input is far greater than the engine. Put simply the system works!

 

[Guest]

[ QUOTE ]
I have currently 2x85AH leisure batteries with a changeover switch and use either for starting 30hp main outboard engine. Am continuously challenged for power on longer/night trips but even in daylight the 70W (max) output generator only contributes say 3/4A at cruising revs and with instruments/radio/vhf I am often running at a modest charge deficit even when motoring and a substantial deficit sailing.
A new wind generator will help keep the batteries topped up, supplimented by a generator when well away from other boats.
I want to get another battery to have more storage capability and my inclination is to get another dedicated starting battery and double up the two leisure batteries in parallel but will this give the alternator or wind generator any problems i.e trying to charge a 170AH battery bank.. I appreciate it is not ideal having batteries connected like this but my whole set up is not ideal and I just have to do the best I can at a low level of cost

any thoughts on this arrangement - better battery configurations or something radical to do with charging on boats?

[/ QUOTE ]

Sorry but had to read through 2 - 3 x 's before could fathom out what you have.

OK .... 1st - it seems your 70W at cruising revs .... ??? That is exceedingly low for an engine alternator. Are you with a Dynastart ? Which would explain such low watts ?

My initial thoughts on reading your post ..... you have very low charge possibilties .......... why ? Are you on Outboard engine ? Are you on older style inboard Dynastart etc. ?

As regards Wind gennys / Solar panels ............ they will charge banks regardless of size as long as they themselves are of sufficient size. Don't expect a trickle charge panel designed to maintain a battery to actually charge it ....

IMHO - it appears you have inadequate charge capacity .......... alternative means need to be sorted ............

You do NOT have to go to Marine Chandlers .......... have a word with Caravan Dealers ........ (and Marine as well .... compare specs and actual equipment .... often its same with different labels .....) Of course I never told you this ..... /forums/images/graemlins/tongue.gif

 

[VicS]

[ QUOTE ]
Are you on Outboard engine ?

[/ QUOTE ] Perhaps you should have read it through a 4th time, Nigel. He says he has a 30 hp outboard!

I think you will find that outboards only have a small alternator (even when fitted with a proper one as opposed to lighting coil and rectifier) I guess they are intended to recharge the battery of an electric start engine and provide enough power for a set of nav lights and maybe a few small extras.

 

[William_H]

The problem lies in the o/b charging system. Most generators have an output voltage that falls with increased load. So if it is rated at 70 watts you will probably finnd that it is only capable of delivering barely 12 volts at just under 6 amps. Now your equipment will run OK at that voltage but the battery will not be charged at that voltage. Indeed current may be taken from the battery because the battery can provide a higher volltage. ie 12.5 volts until it is mostly discharged.

So a larger battery bank will inly delay the point where batteries are discharged. Alternative chargers like solar or wind will recharge the batteries for the next outing.
The real fix is more power (current at regulated voltage) from the o/b charger. It may be worth investigating if later models have a better alternator.
You should of course use an ampmeter and voltmeter on the alternator when running to ensure that it is giving something like 70watts as a failure of a diode can reduce the output dramatically and you be unaware. You should also check the current drain of the instruments radio etc just to make suure there is nothing odd happening. good luck and Merry Christmas olewill