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Author Topic:   Dual Batteries , Switch panel, Terminal Block Location
17 bodega posted 08-14-2006 02:23 PM ET (US)   Profile for 17 bodega   Send Email to 17 bodega  
Re a dual battery switch used with ONE engine. Certain electronics are best wired directly to the batteries according to the instruction manuals. I also understand that the opinion of some highly experienced members here is it is necessary to directly wire certain electronics, like sonar/gps units for example.

I have a six switch panel that feeds off the main battery. Once I install the dual battery switch as [shown] in the Reference Section, I need to decide how to wire the switch panel, and decide whether to add a terminal block or some other device in which to directly wire additional items in the future.

Should I use a BlueSea-type terminal block with four terminals? Or just wire additional things directly to the active battery? On Jimh's diagram he has a breaker switch wired in line from the battery to the engine. Would a switch panel or terminal block be wired along this pathway?

I hope you folks understand my question because it is difficult to articulate in writing what I am trying to achieve. Basically I want to know the best location to place the switch panel and terminal blocks (or both) within the dual battery wiring diagram.

Thanks for any help on this


davej14 posted 08-14-2006 02:51 PM ET (US)     Profile for davej14  Send Email to davej14     

If you wire devices directly to one of the batteries and that battery dies, then you will be left without power to those devices. In my opinion, with a dual battery single engine set up, it would be better to wire all devices to a Blue Seas type terminal block that is connected to the common (+) terminal of your battery switch. Then if one battery dies you can switch to the other or put them in parallel to power the devices. Be sure the battery (-) terminals are tied together and that they and the device (-) connections are tied together on the common buss of the Blue Seas type terminal block. The one exception I would make for this is if you have a bilge pump with a float switch. The bilge pump float switch should be wired to the "house" battery with an in-line fuse or preferably a circuit breaker.

FYI, I also favor removal of any in-line fuses so that the circuit protection is via the associated fuse on the Blue Seas type terminal block. Redundant fuses can be difficult to troubleshoot as they are usually buried in the harness. However, some warranties are voided by the removal of the in-line fuse.

Loafer posted 08-14-2006 03:41 PM ET (US)     Profile for Loafer  Send Email to Loafer     
I generally agree with DaveJ with one exception; I would keep the in-line fuses. They can be a source of failure, especially in a salt environment such as yours. However, I generally go by the rule that the fuse-block (or circuit breakers) protect your wiring and the inline (or in-unit) fuses protect your equipment. You may need a 10 amp circuit for electronics but only a 3 amp fuse for your fish-finder. Just be sure those fuses are in a dry, but accessable place, keep spares and even do preventitive replacement every season.


17 bodega posted 08-14-2006 04:04 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Thanks for the information. Your reccomendations were along the lines of what I was thinking. I'm not sure I totally understand the significance of making sure the terminal block has all the negative leads wired separatley. When I bought my boat, all the negative leads were wired to a common ground pole, and I see this often in older boat setups. This is also how the switch panels are configured. Is there a short explanation of how this is an inferior way of wiring your boat? Should I look to change that setup on my switch panel?

thanks again for the replies.


davej14 posted 08-14-2006 05:36 PM ET (US)     Profile for davej14  Send Email to davej14     
Let me clarify.

I was suggesting that if you use the Blue Sea Systems fuse block, that you tie together all the device commons (-) connections to the common bus on the fuse block. The common bus is then connected to your battery common (-) connection with at least a #10 stranded marine grade cable. The devices that have their own power switch should have their positive (+) connections wired to individual terminals on the Blue Seas Fuse block. The in-line fuse can be replaced with a fuse of the same rating on the fuse block. It doesn't hurt to have two fuses protecting the circuit, it just adds to the number of possible contacts that could corrode and complicates troubleshooting.

If your switch panel has individual fuses then you can feed the switch panel with an appropriately sized single wire from the Blue Seas fuse block. It should be sized and fused to support all loads controlled by the switch panel operating simultaneously. The individual circuits from the switch panel will be fused at the panel for their individual loads. If the switch panel does not have individual fuses then you should run a separate circuit from the Blue Seas fuse block for each switch.

jimh posted 08-15-2006 09:03 AM ET (US)     Profile for jimh  Send Email to jimh     
Advice by certain electronic manufacturers that their devices be wired directly to the battery can for the most part be ignored if there is a proper primary and secondary battery distribution system installed in the vessel. About the only device that would merit its own connection to a battery would be a very high current device like a motor for operating a down-rigger or a windlass. There is no particular reason to wire devices like a 25-watt VHF radio, a GPS receiver, a SONAR, etc., directly to the battery. Boaters who follow the advice of these manufacturers generally have electrical installations which are described by the following industry or technical term: haywire.

The proper location for a secondary distribution panel such as the one you mention is determined by the proximity to the devices which you plan to connect to it. In most cases these devices are located at the helm position, and the secondary distribution panel is located there, too. There is no point in locating a secondary distribution panel far away from the devices it connects. The purpose of the secondary panel is to provide a convenient and local point for connecting these circuits.

In Boston Whaler boats the factory has generally already provided very satisfactory cables connecting the secondary distribution panel to the primary battery switches and circuit breaker. These cables are usually 8-AWG or 10-AWG conductors and will furnish the battery power with very low voltage drop. If you wish to update the original secondary distribution panel with a newer device, the Blue Seas products are a good choice.

17 bodega posted 08-15-2006 01:09 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Thanks for explaining that to the electrically challenged hamburger.. I have a blue sea four terminal block that should work well for my boat.

I would love to see pictures or any diagrams that have been used in this manner so I can see it configured with my own eyes.

Thanks again


17 bodega posted 08-15-2006 11:34 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Switch wiring complete. I assume it makes no difference which battery you wire the negative (-) lead from the switch panel. I wired it to battery #1 on the Perko switch and it worked fine with the switch set to either battery. It's nice to have more peace of mind at sea knowing I don't have to crawl around and change battery leads in case of electrical failure... just hit the switch.


jimh posted 08-16-2006 12:10 AM ET (US)     Profile for jimh  Send Email to jimh     
If there are multiple batteries, the negative leads of all of them should be connected together at a common point, and this should also be used to attach other negative bus leads. However, it is often seen that with two batteries, the two negative terminals are bonded together with a heavy conductor, and other conductors are joined at either battery's negative terminal. This is not the best way, but it is often done in a small boat.
17 bodega posted 08-16-2006 12:49 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Interesting. I do have a negative grounding post that many of the smaller gauge wires from the switch panel attach to, but the larger negative leads are joined as shown in the diagram, with the 10 gauge wire from the switch panel attached to the negative (-) lead of battery #1. Are you suggesting that using the grounding post is a superior method of grounding the switch panel?

Thanks again... I realize this is pretty basic stuff. Pardon my electrical ignorance once again.


davej14 posted 08-16-2006 11:41 AM ET (US)     Profile for davej14  Send Email to davej14     
Your wording is somewhat confusing but I interpret it to mean that you connected your negative (-) switch panel lead directly to the negative (-) terminal of the battery that you consider to be battery #1. Since the negative terminals of battery #1 and #2 are connected this will work.

My own preference would have been to connect the switch panel negative (-) terminal to the same common bus bar that bonds all other (-) connections. Just make sure the bus bar connection has an adequate wire gage connection to the batteries to support all devices running at the same time.

jimh posted 08-16-2006 12:23 PM ET (US)     Profile for jimh  Send Email to jimh     
In wiring practice it is often proscribed that no more than one conductor or terminal should be retained under a screw. To accomplish this there are bus bars with multiple screws available so that a large number of conductors can be bonded together.

The negative terminal of one battery often serves as a common point for the negative bus, and this is accomplished by placing several terminals over the battery post. This violates the recommendation above.

The best practice is to have a battery negative bus bar and to connect all the battery negative terminals to it, each with its own screw fastener. And other leads which need to connect to the negative bus can also be bonded there. You can buy such devices at modest cost.

It is not a good practice to have four or five conductors connected to each battery terminal, and use of these bus bar connectors will avoid it. But, again, we are talking about small boats and not everything is done to the highest standard of ABYC recommended practice. Many boaters have two or three terminals on the battery posts.

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