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I am currently running a 75hp motor. The battery I have is a Century Marine Pro 600. I have read that the deep cycles do not like to go down more than 50%, that is why I figured 100ah, which really gives me 50ah to play with. I agree its better to have too much, and after runnning some basic calculations (watts / volts) I am thinking that I would probably use 20-30amps (roughly) over six hours.
Correct re the 50% charge/discharge. To give you an idea, the Trojan user guide shows that 50% charge is 12.10 volts (compared to 12.73 volts for 100% charge) so that should provide some idea if you have a volt meter on your boat or at home.
Although note that accurate readings should be taken after the battery has been rested/idle for at least 6 hours and preferably 24 hours.
Also your red arc or equivalent systems you can hook up a momentary push button switch which automatically links both batteries together which will aid starting with out fiddling with a main switch
I run one VSR and two part no:2500480 caterpillar batteries are calcium deepcycle(100A/H)/starting(1000cca @27C) roughly landcruiser battery size (N70zz). download one safe source catalogue for full specs very cheap compared to others and good warranty
Do you guys reckon I need a isolator switch or VSR? I plan to charge the 2nd battery using a charger after use. So is there any point even wiring it up isolate the batteries when I dont plan on using the deep cycle for anything but running accessories, and the starter battery for anything besides starting and nav lights.
In my opinion you in the very least need an isolator switch - to switch off all power to the live feeds. Whether you get a vsr is up to you as you can buy a 1, 2, both, off isolator switch and you can manually switch the switch to more or less achieve the same thing as a vsr would acheive except that you have to remember to switch the switch - a VSR/ACR will do this automatically.
I also wouldn't hook up the nav lights to your start battery.
Personally I would instal this add a battery kit containing isolator switch (which keeps the two circuits separate) and ACR which combines on charging.
Also an option is if you set up a 4 way isolator switch you can hook a charger tail up to it so that you can charge either battery by hooking charger to tail and simply switching to whichever battery you want to charge.
Most importantly is to first decide if you actually need to charge that second battery whilst out on the water.
By buying a slightly bigger/better deep cycle and keep it tip top by home charging you can avoid most of the ancillary gizmo's and wiring that can often just be a safety issue itself. 12V SHOULD be kept simple i reckon...you dont seem to have much current needs so just set up a second DC house battery say 80Ahr Deep Cycle kept seperate and run just about everything off that. Sounds like you dont even need a switch. Add a simple 12v digital voltmeter which tells u a basic state of charge and if you start to get much below about 40% left think about turning things off. Nothing essential runs off it anyway. Keep the crank tip top and separate. carry some short jumper leads and invest in a good smart charger and charge at home.
See how u go, THEN decide if u have a need to join the batteries into a full dual system.
Its SUPPOSED to be for safety. Simplicity and reliabilty is safety on the wate. If u dont need something dont complicate it...just having that second battery is a big safety plus. If you dont have a need to, then why connect it up to the other and potentially compromise the entire reason for having a "dual system"...safety.
Yeh I agree deckie. I dont think i really need a switch at this stage. What size wire do you think would be suitable running from a 82ah DC battery? I was thinking something around 6mm 50 amp.
hey shansta...its just horses for courses i reckon. If you do long hauls to the grounds, lots of offshore work etc maybe you'll find charging the new second batt off the motor becomes important to you. But the thing is to spend the $ on a damn good suitable battery first up, suck it and see. Yes better to over estimate batt size, but your current draw isnt too bad unless that stereo is amped up and u like your doof doof loud. The 5050 strip is only 2 m so even if u turn to full on should only draw maybe 2.5A max. Sounders draw sweet fa, vhf a little more, any led nav lights assume only 0.5A each or thereabouts. Stuff that draws are usually things like 12vfridges, spotties, and anything with motors like pumps..but a little bait pump like a 360-500gph only draws maybe 2A. Add up roughly the current draw of what you could have switched on at any one time, multiply that by the 6hr period you say u need e.g 6A x 6Hrs use =36A and get a good deep cycle (that also has suitable crank amps for your donk) thats getting up to about double that in terms of reserve AHrs. That should allow for some addition in the future, but more importantly means u maintain charge on each trip as well as not discharging the battery to a very low state each trip which will help the battery live much much longer. Paying a bit more for a bigger battery often means they last longer anyway...as long as weight isnt a crucial factor and an extra 5kg matters. Bung it on the charger when u get home and maybe leave a float charger on. I'd guess an 70-90Ahr would do you but not a problem going a little more if extra 5kg and some $ isnt an issue.
Usually the wiring size will be determined by how much you draw and the cable run distance to minimise voltage drop. Most guys use the standard tinned 6mm you get at chandlery's and the like to take power from batt to dash,, or if u want to build in extra for the future or its a long cable run then no problems going to 8mm if u plan on serious current usage or maybe as backup for a small anchor winch.....just remember as soon as u go up to 8mm cable then its bigger lugs/connections that arnt the normal over the counter stuff. On most 5m ish trailerboats 6mm tinned should be fine for the run from batt to dash/bus bars/switches, and 4mm for hooking up most things...even 4mm is way overkill for things like led lights.
Soon after putting in maybe do a trail run starting the donk off the #2 new battery or connecting them up to start by assuming your crank is flat/emergency...you will soon find out if you need the full monty dual battery sytem with your usage requirements and boating habits...then at least u already have the right battery good to go if u find you would prefer to connect them up and charge both off the motor whilst out there. Dont know what donk u have but also remember some 2 stks can have quite a low charging capacity anyway...u need to check your donk from the manual. Good luck.
Thanks for the info deckie. Yeh I was thinking 6mm from battery to fuse box/switch and then the tinned 3/4mm for the rest. I ended up buying a 82ah battery, which I think will be suffice.
By donk I assume you mean motor lol - Boating is new to me so I'm not up with the lingo. Anyway I have a 75hp 76 Chrysler, which I have read mixed reviews about these motors, so I was hesitant to buy the boat but bought it anyway. I did a compression test today and all 3 cyc read just over 150psi - the manual says between 145-155 is correct.
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