Charge time batteries ?

[Vronsky]

Hi All,
My motorboat has two 110A lead batteries, and the 115hp outboard has an alternator of 12V/40A >
would like to know what the charge time of the batteries is: is there a website somewhere to calculate this ??

Thanks!
V.

 

[Momac]

How long depends on the state of charge when you start . Could be up to 6 engine hours .

 

[BabaYaga]

Hi All,
My motorboat has two 110A lead batteries, and the 115hp outboard has an alternator of 12V/40A >
would like to know what the charge time of the batteries is: is there a website somewhere to calculate this ??

Thanks!
V.

Assuming both batteries are 50 percent depleted and engine at full revs (=full alternator output) my guess would be about 10 hours to 100 percent SOC.
Based on that the batteries will only accept full output up to circa 80 percent SOC (just over 2 h), then another 8 h is needed to get them really full.
This is why solar makes sense also for motorboats, if shore power is not available.

 

[Vronsky]

I've been considering a solar charger: the roof of my pilot house offers a good spot.
What power would such a panel need to have, just to top-off and maintain 2x 110A lead batteries ?

THANKS,
V.

 

[neil_s]

I find a 30 W panel easily keeps one 115 AH and one 85AH fully topped up.

 

[GrahamM376]

Just for topping up ready for the weekend, 25 - 30w is quite sufficient, could likely get away with less. Depends on your usage, you may need more if weekending on board with fridge, heater etc. and need to top up during use.

 

[Vronsky]

Thanks. No luxuries on board, just the regular necessities..
Would I need a charge controller for such a modest setup? Or hook the panel directly to the battery poles ?

Cheers,
V.

 

[BabaYaga]

You would definitely need a controller.

 

[VicS]

Thanks. No luxuries on board, just the regular necessities..
Would I need a charge controller for such a modest setup? Or hook the panel directly to the battery poles ?

Cheers,
V.

The rule of thumb regarding the need for a controller is that you need one if the ratio of solar power, in watts, to battery capacity, in Ah, is grater than 1 watt per 10 Ah or if the solar power is greater than 10 watts.

If you install 25- 30 watts of solar power for 220 Ah of battery then yes you need a controller on both counts.

However don't fit a basic on/ off controller that simply disconnects as soon as the volts reach 14.4 and does not reconnect again util they have fallen to below 14. Fit a "pulse width modulated ( PWM) controller which will regulate the charging, rather than disconnect it. A bit like having a continuously variable multistage charger.

Or with that much solar power perhaps worth considering a "maximum power point" ( MPPT) controller which will control the solar panels at their optimum performance point.

 

[BabaYaga]

The rule of thumb regarding the need for a controller is that you need one if the ratio of solar power, in watts, to battery capacity, in Ah, is grater than 1 watt per 10 Ah or if the solar power is greater than 10 watts.

However not everyone agrees to that rule, as demonstrated by this rather lengthy but interesting article:
http://www.pbase.com/mainecruising/do_i_need_a_controller

 

[GHA]

Assuming both batteries are 50 percent depleted and engine at full revs (=full alternator output) my guess would be about 10 hours to 100 percent SOC.
Based on that the batteries will only accept full output up to circa 80 percent SOC (just over 2 h), then another 8 h is needed to get them really full.
This is why solar makes sense also for motorboats, if shore power is not available.

For trojans it's more like 4/5 hours from hitting 14.8v absorption with c/20 current available at around 25deg c. From observations on the hook .

 

[VicS]

However not everyone agrees to that rule, as demonstrated by this rather lengthy but interesting article:
http://www.pbase.com/mainecruising/do_i_need_a_controller

I have seen that before. Perhaps I should have said, "A common rule of thumb...."

 

[Mistroma]

For trojans it's more like 4/5 hours from hitting 14.8v absorption with c/20 current available at around 25deg c. From observations on the hook .

Good point and I don't think OP ever mentioned charging voltage specifically. If it's an older alternator he could be waiting days to get to 100% SoC.

I had to tweak both mains charger and solar regulator to get a decent voltage for Trojan batteries. Charging took forever at standard settings. I keep meaning to fix the alternator as well. Fortunately, the solar usually kicks in after the alternator has put a fair bit back into the batteries. OP should really check charging voltage for his alternator and make certain he gets a solar regulator with adjustable settings. I'd have fixed mine years ago if I didn't have wind, solar and a generator as well. His mains charger is probably OK if he is on shorepower all week. Mine is only set high for summer when I'm usually anchor and powering it from a generator.