Two batteries wired in parallel

[itsaboattime]

After reading another post about two batteries, It got me wondering if my set up is the best way to do it.

What I have setup is two batteries wired in parallel - Pos to Pos & neg to neg. I have a high CCA battery connected to the outboard and a deep cycle connected to lights, depth finder, and everything else.

I read on the other post about a switch I can install to control the discharge and charging of the batteries.

How does one of these work?? Is one available here on Iboats?? Are they expensive??

Or do I just stay with what I have. It works, but is the switch a better way?

 

[smokeonthewater]

Re: Two batteries wired in parallel

get an isolater..... it will let the alt charge both but you can run accs off of your deep cycle without running your starting batt down...

You can add a batt switch as well which will let you start from either or both if needed

 

[itsaboattime]

Re: Two batteries wired in parallel

Thanks Smoke.........but how do they work?? I guess I need to find a wiring diagram or sumthin...............lol

 

[smokeonthewater]

Re: Two batteries wired in parallel

well they are basically diodes.... alt hooks to one lug and charge leads to each battery on the other two (or more) lugs.... power can flow out to each battery but not back.... you have to wire it in to the charging system but it is not complicated
basically wherever the alternator connects to the elec system is moved to the isolator
another option is to leave it like it is and disconnect the two batteries from each other..... then you have the choice of charging the deep cycle battery at home or installing a battery switch to connect them while running the engine... problem is that it is a royal pain in the stern to remember to turn that switch on and off all the time and it gets forgotten

 

[smokeonthewater]

Re: Two batteries wired in parallel

click here for diagrams

 

[F_R]

Re: Two batteries wired in parallel

After reading another post about two batteries, It got me wondering if my set up is the best way to do it.

What I have setup is two batteries wired in parallel - Pos to Pos & neg to neg. I have a high CCA battery connected to the outboard and a deep cycle connected to lights, depth finder, and everything else.

I read on the other post about a switch I can install to control the discharge and charging of the batteries.

How does one of these work?? Is one available here on Iboats?? Are they expensive??

Or do I just stay with what I have. It works, but is the switch a better way?

Huh, say what?? You have a cranking battery and a deep cycle battery wired pos to pos and neg to neg (parallel), but then you say the cranking batttery is connected to the outboard and the deep cycle to the lights. Sorry, but that just doesn't make sense. If what you describe is what you actually have, then BOTH batteries are connected to BOTH loads. What am I missing here?

 

[smokeonthewater]

Re: Two batteries wired in parallel

you aren't missing anything except for the fact that that he has recognized that it isn't wired correctly...... Which is the reason he started this thread.... he has the loads wired to the proper batts but then also has jumpers between them yes effectivly having both batts connected to both loads.... It is wrong and the solution is to isolate them from each other as mentioned above

 

[itsaboattime]

Re: Two batteries wired in parallel

Oh sorry......I ment that the outboard is physically connected to the high amp battery and everything else is physically connected to the deep cycle. In the big picture, its all connected together.

You are correct FR, the load is connected to both batteries. I was just trying to state what the connections are.

 

[Silvertip]

Re: Two batteries wired in parallel

If you have a dual battery switch you don't need an ACR or isolator. If you can't handle the meaning of four switch positions (OFF, BAT 1, BOTH, BAT 2) then you need an ACR. Installation of an ACR allows the engine to charge both batteries but it does not allow starting the engine from the other battery if one is dead. A battery switch diagram is shown below and operates as follows: OFF is -- well -- OFF, meaning both batteries are completely disconnected from everything so if you inadvertently leave something turned on you don't come back to the boat and one or two dead batteries. BAT 1 setting means everything on the boat including starting the engine occurs from battery 1 and ONLY battery 1 will be charged. BOTH essentially provides exactly what you have now. The engine can be started using both batteries, both batteries will charge, and both batteries feed all accessories. BAT 2 is the same functionality as BAT 1. Now then -- you get in the boat, set the switch to BAT 1 (typically the start battery) and crank the engine. When it fires you switch to BOTH and go on your trip. BOTH batteries are being charged and all accessories run from both batteries. When you get to your fishing hole, swimming hole, sand bar or wherever you plan to stop, switch to BAT 2 which is typically the deep cycle. All accessories now operate from that battery leaving the start battery isolated so it is ready to go later. Yes, the switches are available here on iBoats for about $35.

 

[itsaboattime]

Re: Two batteries wired in parallel

Thanks Smoke and Silvertip for the wiring diagrams. Now that I see how they are wired, I understand.

And no Silvertip the four positions aren't too much for me to handle. You have to understand, before today I'd never heard of these. So I had no idea what they were all about.

You can bet though, I will have one set up in my boat before spring arrives.

 

[smokeonthewater]

Re: Two batteries wired in parallel

one batt switch does not solve the problem very well..... if you look at the diagram you will see that there is no provision for limiting the accs to just the deep cycle and the eng to just the starting batt at the same time..... the switch works very well for two starting batts or two house (deep cycle) batts but is not very well suited for his application... the acr serves the same purpose as the isolator except that it does not isolate the batteries with the ign on and two unmatched batteries should not be charged in parallel..... The ultimate solution is the batt switch and the isolator.... you leave the start batt wired to the engine at all times and you use the batt switch to wire the accs to both batts..... you can then switch everything on the boat off with one switch you can run accs off either or both batts as needed and by selecting both you can start from both as long as the batts are both connected to the switch with heavy cable..... then the isolator is used to connect the charging system to the batts.... last you install a 3 position momentary togle switch on the dash connecting the batts to your volt guage.... all automatic and you never have to leave the helm to change too mess with your batts

 

[Silvertip]

Re: Two batteries wired in parallel

One battery switch is exactly what he needs and it does indeed allow total isolation of the batteries plug total selection of which battery or batteries he wants to power the boat. All accessories and I do mean all (except the bilge pump) get power from the COM terminal of the switch. Therefore whatever battery (or both if you prefer) will power the boat and be charged by the engine. With an ACR you have no such selection capability. It is merely an isolation device and one way charging device. Handy yes. As versatile as a switch - No.

 

[scutly]

Re: Two batteries wired in parallel

Blue Sea Systems

West Mrne link with a video

this i think is the way to go for 2 batteries. turn it on when you get on the boat and off when you leave. the charging and discharging is switched automatically from start to house as needed. has a combine position also to use in a pinch. ON-OFF-COMBINE. this is perfect for me. i spend my time on the water cruising for a few minutes and hanging listening to tunes for a while then cruise somewhere else and do the same. when i fish its the same. drift move, drift move. i spend the whole day switching batteries and trying to remember to switch them. this is top of my list for this season. gonna make my day a whole lot more enjoyable.

 

[smokeonthewater]

Re: Two batteries wired in parallel

well no point in arguing.....
option 1 isolator and batt switch (I feel this is the best)
option 2 acr and batt switch (scutlly likes this one and it's my second favorite)
option 3 isolator or acr only (my 3rd choice)
option 4 batt switch only (silvertip likes it but I don't)

In the end you will have to decide which one suites you.....

 

[mike343]

Re: Two batteries wired in parallel

If this is really the case--pos to pos, neg to neg--you have no separation between battery loads. Everything is connected together and draws down both batteries.

What I have setup is two batteries wired in parallel - Pos to Pos & neg to neg. I have a high CCA battery connected to the outboard and a deep cycle connected to lights, depth finder, and everything else.

But if the wires to the loads are really separate, the isolator (or combiner) will solve your problem, Remove the pos to pos cable and install the isolator. Please note that it is necessary to make two connections to the alternator, disconnect the pigtail from the alternator regulator input and run a wire to the cranking battery. And put in a single pole single throw switch between the pos terminals for emergency starting.

 

[Silvertip]

Re: Two batteries wired in parallel

Isolators have an inherent voltage drop and are less desireable than the other solutions. I have nothing against an ACR IF it has a combine function so the engine can be started (or that case "jumped" by the second battery. Still not as versatile as a simple battery switch. In most cases the battery switch can be left in the BOTH position until you anchor or leave the boat. Underway the engine will keep both batteries up. If you know for a fact that one of them may be low, set the switch to that position so that battery can take full advantage of the alternator output. Just because an ACR has a "combine" setting does not mean that function will get the engine started if the start battery is dead. A stone dead start battery may not take a jump. It happens far more often than people realize. The switch allows total separation of the two batteries. My preference for a simple dual battery switch is the versatility it provides. It is also the simplest, most trouble-free, and least expensive dual battery solution. Is it the most convenient solution -- No! But in my view it is the capability to work around an electrical issue that is critical on a boat. As I suggest in this and other posts, switches may be too confusing for many folks so it is best for them to rely on automatic devices. Unfortunately, those automatic devices result in some loss of versatility. If true simplicity is what you are after, nothing beats a jump start unit or a set of jumper cables. Cheap too.

 

[smokeonthewater]

Re: Two batteries wired in parallel

Split Charge Diode Block


Instead of using relays, its now possible to use a split charge diode block. The first units produced did use actual diodes, whilst the units worked, they were not efficient due to the voltage drop of around 0.8 - 1.2volts, this doesn't sound a lot, but in terms of charging batteries it is quite a drop. To overcome this voltage drop, the modern units as supplied by Sterling use clever circuitry with mosfets, the result is that the voltage drop is now lowered to around 0.04volts

Split charge diode blocks any problems associated with the above relays and provide a good positive supply to both battery banks, whilst maintaining total isolation between them.

The split charge diode blocks are incredibly easy to install, as shown in the following drawing.

 

[itsaboattime]

Re: Two batteries wired in parallel

I didn't think I was gonna stir up this much controversy. Not sure which way I am gonna go with this, but I will have one of these systems in the boat before the season starts.

 

[dan t.]

Re: Two batteries wired in parallel

go with the switch as Silvertip sujested,simple cheap and foolproof

 

[sickwilly]

Re: Two batteries wired in parallel

Great thread and reading material for those of us thinking of doing this! Thanks!