Battery selector/Automatic charging relay

[Brylk1830]

Hello all,

For the past month I have been doing some research about boating electrical, and although I've come a long way, I have a few more basic questions left

I'm preparing to use two 12v batteries connected in parallel and in such a way as to isolate my starting and house battery. After searching around a bit at the different methods available I narrowed it down between a battery selector switch or an automatic charging relay such as: http://www.westmarine.com/webapp/wcs...classNum=12106

Each of these devices, the selector switch and relay, get wired in a bit different but I have the same basic questions regarding both.

#1.) For the selector switch I can see by looking at the wiring diagrams that it needs to be wired into the starter; I understand how to make connections to and from the battery and bus/fuse panel but I am not sure how to make connections to the engine?
#2.) I've also seen diagrams where each negative of the batteries needs to be grounded to the engine; How exactly do I ground the cables to the engine?

Just by looking at my outboard (Mercury 40 horse 1999 3 cylin) I followed a large black wire from the starter that has a marking to connect it to the batt neg. Also, there is a wire connected to the solenoid that is suppose to be connected to the batt pos.

#3.) Lastly, for switches that need to be wired in with the igniton switch is that going to be the large wire running into my throttle?

Thanks a lot for any suggestions/explanations, I appreciate any help I can get!

These are the specs for my alternator:

 

[Silvertip]

Re: Battery selector/Automatic charging relay

I think you need to study your engine electrical system a little more as I think you don't have this right. To clear things up a little for us, are we to assume you will have three batteries (one start and two house) or two batteries (one start and one house). Here is a diagram as simple as it can get for a simple battery switch.

The two cables going to the engine are the large battery cables from the start battery. The cable connecting the negative (ground) terminals on both batteries must be the same size as the battery cables. Get these at any auto store. There are no small gauge wires involved in this setup. There are no connections to the starter. The connection between the switch and engine is at the starter solenoid, not the starter.

 

[Brylk1830]

Re: Battery selector/Automatic charging relay

http://bluesea.com/category/1/productdocs/9002e

This diagram specifies the switch being wired into the "starter or other load". I've seen a few different ways to wire these switches in.

I posted a picture below with white arrows on the large black wire coming from the starter as well as the black wire coming from the solenoid. When I follow the wire from the solenoid it is marked with "connect to pos terminal" and although the black starter wire is unmarked I imagine it is connected to the negative because there are no other wires connected to my starter battery.

As far as the battery set up I will have two batteries; one for starting and the other the house battery. I've been running this boat for 2 years with only the starting battery and now all i'm really doing is adding the house battery into the equation.

I'm assuming my starter battery has been connected with the alternator all this time so my only real concern is whether I need to run a wire from the alternator as a ground like shown in the relay diagram. The reason i'm confused is because like I stated earlier the only to wires that have been connected to my house battery all this time are the two wires (from starter and from solenoid). Is my starting battery already grounded to the engine? If so, is the alternator somehow connected into the wiring of the starter?

Sorry if i'm being confusing but i'm a bit confused myself !

 

[Silvertip]

Re: Battery selector/Automatic charging relay

The switch you showed the link for is an ignition protected switch which you don't need. The large black wire in your picture is the ground cable that runs to the NEG terminal on the start battery. You need another cable from that terminal to the NEG terminal on the second battery. There should be a large red cable (the same size as the ground cable) running from the starter solenoid to the COM terminal on the switch. The same size cables would be run from the POS terminal on each battery to the #1 and #2 terminals on the switch. All accessory loads would be run to the COM terminal. That's the typical configuration and offers the most versatility of the switch. You can charge either or both batteries, run accessories off either or both batteries, and shut off power completely to the entire boat. The only accessory you want wired directly to one of the batteries is the bilge pump if it happens to be an automatic type.

 

[Brylk1830]

Re: Battery selector/Automatic charging relay

Thanks Silver, I made this quick wiring diagram to make sure this is the connections you were talking about. If that looks alright than I think i'm good to go. When you say wire in all the accessories to the common switch do you mean just run a wire from the common to the positive bus? Thanks again!

 

[Silvertip]

Re: Battery selector/Automatic charging relay

On the Positive terminal of the start battery you should find a smaller gauge (probably 6 or 8 gauge) wire that feeds +12V to the fuse panel. That wire would be disconnected from the start battery and connected to the COM terminal on the switch. Therefore all accessories could be powered from BAT 1, BAT 2 or BOTH, or all disabled (OFF). Your diagram is exactly like the one I posted. Go for it. Just so you know how to used the switch here is a typical scenario:

OFF: At the dock or on the trailer, boat not in use.
BAT 1: Typically this is the start battery and it is providing power to everyting. Only that battery will be charged with the engine running. Start the engine in BAT 1 position or BOTH. In the BOTH setting, underway both batteries will be charged. If you know that one battery is relatively low, you can switch to that battery so the full output of the charging system goes to that battery.
BAT 2: Same as BAT 1 except you would typically use this setting when you are anchored and listening to your megawatt stereo or using other accessories. This prevents discharging the start battery (BAT 1).
BOTH: Typically used under way so both batteries are being charged. If you are not anchored for long periods you can leave the switch in BOTH mode and just enjoy the day. There is no way you can discharge two batteries in just a short period of inactivity.

 

[Brylk1830]

Re: Battery selector/Automatic charging relay

Silver if you're still around I began making my wiring diagram and was wondering if it matters now which battery my negative bus wire comes from?

 

[Silvertip]

Re: Battery selector/Automatic charging relay

No. Ground is ground. It doesn't matter whether you attach it to BAT 1, BAT 2 or the engine block. Electrically, they are all the same point. Why? Because they all connected by cables. You obviously don't want to connect it to the engine block because of the inconvenience so the NEG terminal of either battery is fine. Just remember, both battery NEG terminals need to be connected together.

 

[45Auto]

Re: Battery selector/Automatic charging relay

Here's how I wired my ACR. Didn't separate it into a house and starting battery, just kept #2 totally isolated (except for auto bilge pump, have 1 on each battery) so if I run down #1 I just switch to #2 and it's fully charged, ready to go. Works great, both batteries stay fully charged without having to remember to switch between them.