Primary Power Distribution

Electrical and electronic topics for small boats
jimh
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Primary Power Distribution

Postby jimh » Wed Mar 27, 2019 4:14 pm

Here is a sketch showing wiring for primary power distribution for a boat with two 12-Volt batteries and one outboard engine:

primaryPowerDistributionSketch.png
Fig. 1. Primary power distribution with two batteries, one engine with auxiliary charging output.
primaryPowerDistributionSketch.png (52.73 KiB) Viewed 187 times

As shown above, the outboard engine has an auxiliary charging output. This is a common option on modern outboard engines, and it permits the engine to independently charge two batteries without having to put their loads in common.

A general goal of the layout of the wiring has been to keep the number of terminals fastened under a terminal post to one whenever possible. The only instance in this design where more than one terminal is under a fastening post is at the battery terminals themselves. However, some batteries have two sets of terminals, SAE and threaded-post, so if batteries of that type are used there will only be one terminal under each fastener.

I will go over the individual components, discuss their functions, and recommend suitable devices in a few follow-up posts.

jimh
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Re: Primary Power Distribution

Postby jimh » Wed Mar 27, 2019 4:37 pm

PRIMARY BATTERY SWITCH

The switch is a modeled after the BLUE SEA SYSTEM "Dual Circuit Plus" Model 5511e switch. There are four terminals on the switch: two for batteries, and two for loads. The switch has three positions. In the OFF position no batteries are connected to any loads. In the ON position, B1 connects to L1 and B2 connects to L2. In the EMERGENCY position, B1 and B2 are both connected to L1 and L2. The normal operating position is ON. The two batteries are isolated, as are their loads. If the starting battery does not have enough charge to crank over the engine, the switch is moved to EMERGENCY, paralleling the batteries temporarily for engine starting.

The Model 5511e has mounting holes that will align with the mounting holes of many legacy battery switches. This makes the model 1155e a good choice when revamping an older boat's electrical system; it will not be necessary to drill new mounting holes for the battery switch if the battery switch is to remain in the same location.

https://www.bluesea.com/products/5511e/e-Series_Dual_Circuit_Plus_Battery_Switch

jimh
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Re: Primary Power Distribution

Postby jimh » Wed Mar 27, 2019 4:42 pm

TWO-BANK 120-VAC CHARGER

Having a means to charge the boat batteries from 120-VAC that is permanently installed is very useful. There are many choices for a 120-Volt AC powered two-bank battery charger. For many boaters, a high-current charger is not necessary. A two-bank charger with a modest charging current of 5-Amperes will often be sufficient to replenish any lost charge in the boat batteries if left on for a few hours.

A charger with fused outputs is recommended. For long-term storage, as in winter, the charger can be completely disconnected from the boat batteries in order to reduce any stray load currents by removing the fuses in the charger leads.

My own boat has a ProMariner two-bank charger that has worked well for many years. It has 5-Ampere charging. The typical use is to operate the charger from 120-VAC with an extension cord. If the boat has not been used in several weeks, I typically top-off the battery charge for a few hours before heading to the launch ramp. If the boat is in use and we are staying overnight at a dock or marina with 120-VAC power available, I use the charger to provide power to the batteries while we use cabin lighting in the evening.

jimh
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Re: Primary Power Distribution

Postby jimh » Thu Mar 28, 2019 3:35 am

12-VOLT LEAD ACID BATTERIES

The starting battery should be selected to meet the outboard engine manufacturer's requirements for delivery of current. The rating is usually provided in either Marine Cranking Amperes (MCA) or Cold Cranking Amperes (CCA), which are ratings for short-term delivery of current with a specified limit on voltage drop at various temperatures. The MCA rating is specified at 32-degrees-F, which is probably colder than most people will ever use a boat. The CCA rating is specified at 0-degrees-F, which is extremely unlikely to be encountered in boating. A requirement for a rating of 1,000-MCA is typical for larger modern outboard engines. Starting batteries are designed for shallow discharge during starting and then immediate recharging from a running engine.

The house battery should be selected to meet the anticipated house loads. On small outboard-engine boats, house loads will be modest and will consist mainly of electronic devices and lighting. House batteries are usually selected based on their rated storage capacity, measured in units of Ampere-hours. A house battery should also be useful as an engine-starting battery in an emergency, to be used in parallel with the normal engine cranking battery. A house battery may be designed for deep-discharge and have a rating of 40-Ampere-hours or more. If the engine cannot be started by pull starting, the house battery should be chosen with the idea it may have to be the engine starting battery if the normal starting battery has completely failed.

Because the batteries will be charged by the outboard engine whenever the engine is operating, I recommend avoiding use of gelled electrolyte batteries. Batteries with gelled electrolyte require particular charging voltages, and most outboard engines provide no means of adjustment of their charging output voltage. A conventional flooded-cell vented lead-acid battery is the least particular about charging voltage. For modern outboard engines with well-regulated charging voltage output, sealed batteries can also be used. Use of sealed valve-regulated lead-acid (SVLA) batteries is now common. SVLA batteries with absorbed glass mat construction (AGM) are also popular. SVLA AGM batteries with thin-plate and ultra-high-purity lead (TPUHP) are the top-line of marine starting and house batteries.

For many years I used conventional lead-acid flooded cell vented batteries, but I have now switched to AGM batteries. Because of the location of the batteries in my boat, removal of the batteries is somewhat awkward. I leave the batteries in the boat during winter storage, rather than removing them and bringing them indoors. For a starting battery I use a high-purity lead-acid AGM. An advantage of high-purity lead construction is very low self-discharge rate. Over more than eight-months of non-use, the high-purity lead batteries show very little self-discharge. Cold weather also reduces the self discharge rate.

For many years an excellent value in a marine AGM battery was found at Sears with their Diehard Premium Marine AGM battery that often sold at a discounted promotional price of $175. I bought one in 2010, and that has been my boat's starting battery for ten seasons. The equivalent replacement available today sells for about $325 and not from Sears but from a battery specialty store. AGM batteries can be easily shipped, so they can be bought as mail-order products now, whereas most other batteries must be bought in person at a battery retailer.

jimh
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Re: Primary Power Distribution

Postby jimh » Thu Mar 28, 2019 3:48 am

AFT POSITIVE and AFT NEGATIVE SECONDARY BUSES

For a HOUSE battery located in the stern of the boat, having local secondary distribution buses will be convenient for connecting secondary loads which are located nearby. These fused loads will usually be sump pumps which are controlled by automatic switches. The aft negative bus can also be useful for house loads that are controlled at the helm but are located near the stern, such a navigation lighting. The negative circuit for those loads can be connected to the aft negative secondary bus instead of running back to the helm.

The Auxiliary Charging Output of the engine is also connected to the HOUSE battery by a fused connection to the aft secondary positive bus.

For many iinstallations, a Blue Sea System model 5025 6-circuit fuse panel with negative bus can fulfil the role of the aft secondary positive and negative buses.

For aft loads with higher current demands such as electric propulsion motors ("trolling" motors) or large pumps, a Blue Sea Systems model 8690 Battery Management Panel may be useful. This panel will combine the primary battery switch, the house circuit breaker, and several fused secondary loads into one panel.

I found the instructions for the Model 8690 battery management panel were difficult to download from the manufacturer's website, and I have linked a copy of the instructions to this article below:
Instructions for Blue Sea Systems Battery Management Panel in PDF

The model 8690 includes the mounting panel and these accessories:
  • (1) model 5511e dual battery switch
  • (2) model 7056 push button reset 15-Ampere circuit breakers
  • (1) model 7549 C-series flat rocker 100-Ampere circuit breaker
  • several 4218 square format labels
  • several 4140 24-hour round labels

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Primary Power Distribution

Postby jimh » Thu Mar 28, 2019 4:04 am

HOUSE DISTRIBUTION PANEL

Even on a small boat, a house distribution panel with 12 fused circuits is not excessive. The loads typically will be electronic devices, such as a VHF Marine Band radio, a SONAR, a chart plotter, and lighting loads, such as navigation lighting, cockpit lighting, and cabin lighting. Sump pumps are also typical house loads. The Blue Sea System model 5026 12-circuit blade fuse with negative bus and cover is a good choice.