Understanding batteries on a boat

[Privilege]

Rekkabell,

As with most questions posted on the forum we often go off on a tangent...sorry!

I also think that things may be getting a little too technical for you so here's a beginners version...
A decent battery charger has the ability to charge in three stages; bulk when the battery needs most charging amps, absorption for when the battery is almost full and float for when the battery just needs to maintain a full charge. The charger knows which one and feeds the necessary amps to the battery accordingly. Therefore, the general rule is to leave it on all the time. A battery only has a limited number of cycles so depleting it and recharging it will eventually kill it. Leaving the charger on all the time prevents the cycling. If you power up a 12v device while the charger is plugged in, rather than draining the battery, the charger kicks up a notch and provides the extra power for the device and that's what probably happens when your hear the charger's fan kick in.
So, a basic answer to your question is; 'yes' I would keep my charger on at all times.

[conachair]

Originally Posted by btrayfors

I agree completely. Not only is reliable load testing time-consuming and a PITA, but it is EXPENSIVE as well.

Consider this:

1. a variable & preferably programmable electronic load device which presents the desired purely resistive and constant load to the battery under test;

2. calibration steps to be sure the voltage and amperage values are accurate over time; and

3. a means of disconnecting the load when the battery voltage reaches 10.5VDC.

Given the right programmable and automated equipment, such as the Array Load tester used by MaineSail, this CAN be done on a boat, but it's still a pain and is still expensive.

Unfortunately, there's no other reliable means to measure residual capacity of a battery or battery bank, though there are proxy indicators which with sufficient knowledge and experience MAY help in estimating battery health.

Bill

Slight drift, but it doesn't *have* to be expensive. If you're DIY electronics inclined that is
All that can be achieved accurately and log the data as well for the cost of a few beers using something like an arduino plus a few more components from ebay. One unknown though, would PWM control of FET's controlling the load make a difference?
Where it really does get tricky and where only the likes of mainesail can really do it properly is keeping the battery at a constant predetermined temperature.

[FlippedPip]

Originally Posted by Privilege

beginners version...
A decent battery charger has the ability to charge in three stages; bulk when the battery needs most charging amps, absorption for when the battery is almost full and float for when the battery just needs to maintain a full charge. The charger knows which one and feeds the necessary amps to the battery accordingly. Therefore, the general rule is to leave it on all the time. A battery only has a limited number of cycles so depleting it and recharging it will eventually kill it. Leaving the charger on all the time prevents the cycling. If you power up a 12v device while the charger is plugged in, rather than draining the battery, the charger kicks up a notch and provides the extra power for the device and that's what probably happens when your hear the charger's fan kick in..

As a newbie myself, thank you for the beginners version. Now it makes more sense.

[exMaggieDrum]

Originally Posted by conachair

Slight drift, but it doesn't *have* to be expensive. If you're DIY electronics inclined that is
All that can be achieved accurately and log the data as well for the cost of a few beers using something like an arduino plus a few more components from ebay. One unknown though, would PWM control of FET's controlling the load make a difference?
Where it really does get tricky and where only the likes of mainesail can really do it properly is keeping the battery at a constant predetermined temperature.

I'd say I am more electrically inclined, with a lot of professional experience, and have been a very minor electronics enthusiast, but I would say putting together anything with arduino would not only be technically challenging to 95% of the cruisers out there as well as being intimidating to most. I could put something together but I wouldn't trust it to do anything critical. More for FYI usage. Just my two cents