Dual Battery Setup and Battery Charging

[skronkman]

In regards to having the batteries of the same CCA. I don't believe this is as big of an issue as it sounds. You won't be running your batteries in parallel all the time, they just wind up in parallel sometimes when being used or charged. It is more relevant to batteries in permanent parallel configurations but you do not want this as it no longer provides many of the benefits of dual batteries (like redundant starting ability).

However You must be sure that your batteries are the same chemistry so that the voltages for charging are the same. I have done many setups with batteries of different capacities that wind up in parallel and had no issues. It is a very common practice but I believe it is recognised that it may not be ideal but is still practical in the real world. My previous boat had a start battery and a separate deep cycle battery of very different AH/CCA that charged via VSR and never produced any noticeable problems. My current boat, I admit, has 2 exactly the same batteries in it but this was by chance as I got a good price on the batteries. It is a different story when putting batteries in series but this is not the case we are discussing.

For a more technical look at this exact issue see : http://neuralfibre.com/paul/wp-content/ ... ow-sin.pdf

[skronkman]

Not sure about tohatsu outboards but usually its just under 2k? Don't quote me though..

Typically the alternator will put out what it can at lower rpms but doesn't reach full current until around 1800rpm. At idle there is more than enough output current to put some charge into the battery if there is minimal load ie sounder radio and motor running.

This is true and easy to see if you have the ability to see your battery voltage. At low rpm it will be around the voltage of the battery charge state, after you get the revs up (1500 or so) you will see the battery voltage increase until it hits the regulators charging voltage (around 13.8 to 15 volts depending on the motor/regulator)

When you want to use your anchor winch it is a good idea to start the engine and increase the idle up to around 1500 before weighing the anchor as then the winch runs entirely from the alternator and doesn't drain your battery at all. This can be seen again by monitoring the battery voltage as you use the winch.

[smile0784]

While we on the topic.
In my 5.7mt trailcraft boat i dont.
Should i have a battery guage on the dash?
Should i have a separate guage for each battery or doesn't really matter for size of the boat?

[skronkman]

While we on the topic.
In my 5.7mt trailcraft boat i dont.
Should i have a battery guage on the dash?
Should i have a separate guage for each battery or doesn't really matter for size of the boat?

Your sounder or gps likely has an option to show battery voltage, you may just need to enable it in the settings. If you switch your battery selector from 1 to 2 you can see the voltage of either battery with the one gauge (this depends a little on how your dual battery setup is configured and may not work if you have one battery permanantly configured as a house/aux)

Whilst I am constantly monitoring the battery voltages for signs of troubles I dare say it is because I have a background in electronic engineering and have historically taken an interest in particular in battery charging technology. So I guess I kinda know what I'm looking for when I look at the gauges. In my opinion Everyone in a boat that depends on their battery for safety should have a basic understanding of the battery voltage relationship with its state of charge and what voltages indicate under different battery usages and conditions (chargin,resting,heavy load,etc.) this could help prevent getting yourself into a dangerous situation.

[smile0784]

While we on the topic.
In my 5.7mt trailcraft boat i dont.
Should i have a battery guage on the dash?
Should i have a separate guage for each battery or doesn't really matter for size of the boat?

Your sounder or gps likely has an option to show battery voltage, you may just need to enable it in the settings. If you switch your battery selector from 1 to 2 you can see the voltage of either battery with the one gauge (this depends a little on how your dual battery setup is configured and may not work if you have one battery permanantly configured as a house/aux)


Thanks
I didint know that i could do that.
I will have a look when i get into the boat next time.
I have a 3 way switch so we good to know if voltage it going down when running the lights ect when night fishing or when out game fishing with the freezer running.

[sturgeon]

Does the simrad go 7 have that battery volt moniter function.

[spudtrans]

thanks guys and girls, there is some great info and tips here. i admit i am learning a lot about my setup
cheers spudtrans :a_goodjob:

[skronkman]

Does the simrad go 7 have that battery volt moniter function.

Looks like it does in the manual. Go to a dashboard, bring up the menu, select edit, select battery and then enable the voltage display. Page 95/96 in the manual.

[sturgeon]

Does the simrad go 7 have that battery volt moniter function.

Looks like it does in the manual. Go to a dashboard, bring up the menu, select edit, select battery and then enable the voltage display. Page 95/96 in the manual.

That's great. Saves me having to install a battery moniter. Thank you!

[Hydroman]

Was just on the century pro website. https://www.centurybatteries.com.au/pro ... ualbattery
It says for dual battery system, they recommend that the second battery be deep cycle. If that is the case, it will not be possible for both batteries to be exactly the same. So which deep cycle can I use to pair with the 680?

I understand where they are coming from but it all comes down to the setup you want to run and probably not a one setup fit all scenario. They recommend deep cycle for a house battery as deep cycle is the best for slow draining. My setup, excluding the portable fridge that I only use if really hot, I am lucky to drain 3 amp-hour so the drain off the house battery is negligible over maybe 3 hours before starts. I therefore do not need the long term drain capabilities of a deep cycle as I am not stationary for the drain to be a concern and I personally like the idea of the 2nd battery being a start battery for backup. Just my opinion.

I just looked at the Suzuki and they do not recommend deep cycle batteries and the two batteries should be of the same specification when connected in parallel.