Best way to wire batteries?

[jafo9]

I've done some research on this and as usual, I've gotten myself confused. I've attached some pictures of my boat. The main battery is in the usual location on the port side under the sunpad. It is currently wired so all house power except the 12V fridge runs off of it. In the little kitchen area is another battery and its own charger. It is dedicated only to the 12V fridge. This seems like a waste. My optimal setup would be to move all house functions to the second battery in the kitchen area on the starboard and keep the 12V fridge there as well. To accomplish this, I plan to add the Blue Sea Systems "Add A Battery" kit.

http://www.overtons.com/modperl/pro...Circuit_System&str=add+a+battery&merchID=4005

I'm assuming this will allow me to safely isolate the starter battery from the house current draw while anchored but when underway, allow the boats alternator (Honda BF225) to charge both batteries.

Then to make things more complicated, I'd like to maintain the ability to keep the charger. The cheapest option would be to keep the current 10amp charger. Is it possible to use it to charge both batteries with the Perko switch in "combine" mode? Or do I just leave the current charger attached to the house battery and buy another battery charger for the port side? Or should I buy a dual bank charger?

Thanks for any input.

 

[Greg Mrozinski]

Re: Best way to wire batteries?

Jafo,

This seems like a reasonable thing to do but you need to do some research first. First off you need to figure the total combined (existing plus frig) projected load on your new single house battery when you are parked and having fun (amp-hour load). This will give you an idea of how long your house battery will last before needing recharging. Then you need to determine what size and type of battery you will need to fullfill your requirement (i.e. combination starting and deep cycle, deep cycle only, size of battery, gel cell, AGM cell, Wet cell, amp-hr rating, etc.). Once you have determined your battery types and sizes, then you need to determine if your engine alternater has enough output and proper internal regulation to adequately charge the batteries selected. Gel, AGM and Wet cell batteries all have different charging profiles and requirements. Most OEM alternaters cannot adequately charge larger deep cycle batteries properly. The Blue Sea Systems "Add A Battery" kit you are looking at is fine for a dual bettery set-up. It will automatically direct charging to the battery that needs it most while the engine is running (and if of course the alternater can properly charge the battery). For shore power power charging, I would recommend switching to a dual charging charger with the capability of charging multiple types of batteries at the same time. That way you could have an larger AGM deep cycle house battery and a marine starting battery in the same system and the charger will automatically adjust charging accordingly. There is a lot to think about I know but all this stuff is expensive and you don't want to waste money by not properly matching components.

 

[jafo9]

Re: Best way to wire batteries?

great points. i'd didn't extrapolate that much. i just assumed my draw was so low it wouldn't really matter. we don't do any overnight trips, so really it will just be the radio (no aftermarket amps) driving basic marine speakers and the 12V fridge. occasionally we anchor at night and would then need the courtesy lights and mooring/nav lights.

from the igloo site they quite about 5 amps draw. the battery currently dedicated to the igloo cooler is a deep cycle 690 amp battery. the main battery that currently does the motor and house stuff is 825amp. best info i can find on the motor is a 60amp (756W) charging system on my 02 Honda BF225.

does this sound like too much of a load? thanks.

 

[Greg Mrozinski]

Re: Best way to wire batteries?

jafo,

Let me see if I can break this down a little. These are the things you need to look at:

1. Amp Hour rating - what is the amp-hour rating on your existing frig battery (this not the CCA or cold cranking amps). All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour and it is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The accepted AH rating time period for most batteries is the "20 hour rate". This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. So in your case with just the radio and frig you are looking at about an 8 amp draw. A Group 27 size deep cycle battery will have about 90 amp-hours available. So 90 amp-hours/8 amps gives you 11.25 hours of use. Now in real life you don't want to fully discharge your battery, so the total amount of discharge should be kept at about 70% max. So your actual run time should be no more than 11.25 hours x .70 = 7.8 hours. This is a simplified example using only the radio and frig. If you have other electronics/lights then they have to be considered. Depending on the size of your frig battery you might be okay already if you are frugal.
2. Battery Type - this up to you. Wet cell (lead acid) batteries work well but don't last as long as AGM or Gel cells (both in amp-hours and life span). AGM and gels are more expensive but last longer (can handle more duty cycles). I personnaly find AGM deep cycle batteries to be the best all around house batteries. You could stick with what you have and then upgrade when replaced.
3. Charging - If you go with two batteries, one starting main and one deep cycle house you should be able to charge these from your alternater. They will not charge at the same time but they will individually and the Blue Sea switch combined with the ACR should work if you battery sizes stay nominal (Group 24 or 27). Just remember though that you will have to run your enigne at moderate speeds to charge your house battery. The charge time may be longer than your actual boat run out or home. Shore power charging can be accomplished using a dual bank charger rated at 20 amps. Anything smaller might not work and the bigger one will charge faster. Get a charger that can charge mutiple types (Gel, AGM, wet cell) of batteries in the same system.

You didn't mention how your batteries are currently "switched" or which ones get charged by the motor vs. shore power. Since you will need to connect the other house loads to the house battery, you might want to make a sketch of how you want to wire things so you have a reference sheet.

Head hurt yet???

 

[jafo9]

Re: Best way to wire batteries?

thanks for the reply. yes, my head hurts. the boat is currently wired where the fridge was an add-on type option. so basically every thing is wired to the main battery and the alternator charges the main battery. inside the entertainment cabinet, there is the 10amp charger and the spare battery. the only draw on the spare battery is the fridge and the only client of the charger is the spare battery. so, the main battery and the 2nd battery are currently totally independent. i just figured since i already had the batteries, i could add a little safety.

we are usually only out max 8 hours a day when we are at the lake with usually 20min or so of runtime between stops. more if we are skiing. our stops rarely last more than 4 hours. our dock has shore power so in the past, i've just plugged in the fridge charger and left the fridge running to keep it cool overnight.

so the 2nd battery is a group 24 battery, its brand is Interstate and according to their website, at a 5amp draw, it should last 16.4hrs, at a 15amp load, it should last 4.6 hrs. if I muliply the amp x hrs i get 82 and 69 ah respectively. am i doing the math right? i'm assuming i'm making a mistake somewhere as the numbers don't come out the same.

thanks again for your help.

 

[Silvertip]

Re: Best way to wire batteries?

Perhaps I can provide another way to look at the "load" situation. If you look at the label on the fridge (house) battery, being a deep cycle, it should indicate what the "Reserve Capacity" is. This is a number expressed in minutes and represents the amount of time the battery will maintain voltage with a 23 amp load. A group 27 size deep cycle will be in the vicinity of 145 minutes. What that means is the battery will power a 23 amp load for 145 minutes or a little shy of 2-1/2 hours. 23 amps is a fairly hefty load, so if all that's running is the fridge at 5 amps, that's roughly 1/5 of 23 so the run time would be well over 10 hours which is within the timeframe you say your are typically on the water. Starting batteries are rated differently so the Amp/Hour rating is needed for those calculations. In my view, you are a prime candidate for a dual battery switch. OFF is off. BAT 1 setting (usually the start battery) means it is powering everything on the boat and the engine is charging only that battery. BAT 2 (the house battery) means it is powering everything on the boat and the engine is charging only that battery. BOTH means both batteries are on line and both are being charged by the engine. So the routine is to switch to BAT 1, start the engine, switch to BOTH and run to your destination. Enroute, both batteries are charged, your fridge is happy and all accessories don't care where the juice is coming from. At your destination, switch to BAT 2. The fridge and all accessories now run off the deep cycle and the start battery is protected from discharge. When ready to go, switch to BAT 1, start the engine and then switch to BAT 2. Why BAT 2? Because it is the most deeply discharged and it will then receive every amp the alternator has available. The start battery can start your engine for a week before it would need to be charged so it is generally not an issue.

 

[jafo9]

Re: Best way to wire batteries?

Ok, so here's what I've done. I've added a Bass Pro Shops labeled (rebadged promariner) 10/10amp dual charger with each set of dual leads to the positive and negative terminals of the 2 batteries. I have purchased the "Add A Battery" kit from BlueSeaSystems. Below is the diagram in B&W that is in the instructions. The color diagram is my wiring diagram. I'll use the same gauge as what is coming off my motor for the thick lines (not sure of the gauge but the alternator is less than 80amps). the wires off the charger are what were included in the package. the smaller low amp runs will likely be 14 gauge. since the switch in the kit is different than the traditional 4 position switch that just has a common "+" pole, I haven't been able to find a diagram similar to mine is the posts i've searched through. the switch in this kit just has a "on", "off" and "combine" setting. the combine just shorts the 2 sides of the switch. the on setting leaves 2 separate circuits allowing the ACR to sense a voltage above 13.5volts and then allow current to flow from starter battery to the house battery. does this look correct? have i just planned a fireball? i haven't drawn in the recommended fuses but I plan to put them in. along those lines, do I need all the fuses they recommend (likely a stupid question, but i'm good at those). thanks.

 

[Silvertip]

Re: Best way to wire batteries?

Why do you show the ignition switch in the ground line from the helm. Really, all you need to do is wire the add a battery kit like the diagram shows. Add your charger the way you show it. Add the fridge to the and helm tow whichever battery you want. Except for the ignition switch it would appear this will work as intended. I would strongly suggest circuit reset style breakers rather then fuses wherever you add them.

 

[jafo9]

Re: Best way to wire batteries?

re: ignition switch. in the text they say that to enable the starter isolation mode you have to run a low voltage wire from the SI tab on the ACR to the wire that becomes positive when the starter is engaged. they recommend tapping into that wire at the key switch or at the starter itself. it just seemed easier to get to the back of the key switch.

re: fridge. the reason the fridge runs separately is that is the way the boat is currently wired. in my helm, i don't have a distribution panel to tap into. it's an '03 and apparently came wired from the factory that way.

thanks for your reply. i tried to follow the instruction diagram as closely as possible, given my current configuration. I don't have a negative bus for the batteries and I don't have a distribution panel in the helm (my assumption is that there are so few accessories). thanks for the suggestion on the breakers. where is a good place to buy them? I have a west marine and a grainger in town. thanks again.

 

[Silvertip]

Re: Best way to wire batteries?

You show that as a ground wire! Ground wires do not become active when the key is turned on. You do not measure 12 volts on a ground wire because it is --- well --- ground. Circuit breakers are available anywhere boating supplies are sold including right here on iBoats. Circuit breakers for each device should be installed at the source of supply voltage for that device. That is NOT at the battery unless the device is fed directly from the battery.

 

[jafo9]

Re: Best way to wire batteries?

i apologize. after my last post, i realized the problem was likely that i made the wire from the ACR to the ignition switch black. when i was making the diagram, i wanted to use yellow, but i figured it wouldn't show up. i should have chosen red instead.

i don't think any of my devices have breakers. i think they all have in line fuses. i really don't like the way they are wired. my last boat (sun tracker) was much more elegant.

on the diagram, for the fuses they call for that will be either 60 or 80 amp, should i be looking for circuit breakers there also? i've found nice terminal fuses from blueseasystems that would work.

here's an updated wiring diagram.

 

[Silvertip]

Re: Best way to wire batteries?

60 - 80 amp breakers will set you back about $35.00 a pop so if you've located blade style fuses you may as well stick with them. As for the red vs black wire, your diagram made it look like the ignition wire and the ground wire from the battery were connected at the same place. Apparently they are not.