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ContinuousWave Whaler Moderated Discussion Areas ContinuousWave: Small Boat Electrical Charging A Second Battery
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Author | Topic: Charging A Second Battery |
carlo2533 |
posted 03-15-2011 02:06 PM ET (US)
[I] just bought a 2010 [Boston Whaler 190 MONTAUK] with VERADO 150-HP. [I] want to add a second battery for radio, electronics, and piece of mind. [W]hat is the best way to do this so the alternator charges both batteries? |
jimh |
posted 03-15-2011 05:23 PM ET (US)
I think the best way to maintain charging to a second battery and keep it isolated from the primary battery is to have an auxiliary charging output from the outboard engine. I am afraid that I cannot tell you with any certainty if your Mercury VERADO engine provides that option. My guess--only a guess--is that it does not. If lacking an auxiliary charging output, the next best way to maintain charging of a secondary battery is to use an automatic combiner relay (ACR)--sometimes also called a voltage sensitive switch (VST). The company BLUE SEA SYSTEMS makes a very nice ACR and has excellent technical literature that describes how to properly install it. The drawback to an ACR compared to having an auxiliary charging output from the engines is: --the ACR installation is rather complex if you follow the recommendations, which require a multitude of fuses to be used, creating many additional connection points and wiring problems; and, --the ACR places the two batteries in parallel, thus defeating the purpose of having isolated electrical distribution between engine and accessories. To help prevent engine starting voltage spikes from affecting the isolated battery and its loads, a further complication has been added to the ACR function, called "starting isolation" or "SI" for short. This adds additional wiring complexity and more fuses, but an ACR with starting isolation is the best way to accomplish more isolation between electronic loads and the engine starting battery. BLUE SEA SYSTEMS has a good website found at Read about the BLUE SEA ACR with starting isolation at |
deepwater |
posted 03-15-2011 06:09 PM ET (US)
What I did was add up all the amps at max draw from all my electronics I wanted isolated and I got a lawn tractor battery that was way over that and wired everything to a separate buss strip with fuses and run them all from that battery,,I took it home after a long trip and put it on a battery tender and it was ready the next trip,,Battery weight 12lb approx and about $22 |
jimh |
posted 03-15-2011 07:10 PM ET (US)
The advice sought is "Best way....so that alternator charges both." Adding a second battery that is not charged by the outboard engine is not a good solution. |
lakeside25 |
posted 03-15-2011 08:20 PM ET (US)
If you dig deep into the Blue Seas website and look for the Application Briefs you'll find some great "how to" articles such as ... http://bluesea.com/viewresource/526 Read the complete series. |
Jefecinco |
posted 03-16-2011 09:44 AM ET (US)
Carlo, A satisfactory method that is fairly simple and relatively inexpensive is what I use. It requires two batteries, a four position selector switch with the following positions: Off, Battery One, Battery Two, and Both Batteries. Some additional battery cable and terminals are also required. I recommend the use of AGM batteries and they are recommended by Mercury for use with Verado engines. There are several good brands available but Sears Diehard AGMs are high quality with a good warranty and are priced within reason. There are wiring diagrams available so I won't try to provide one. If it is not overly complex I recommend dedicating one battery to the engine. Call that battery "One". Dedicate the second battery to the other electrical loads such as electronics and lights. Call that battery "Two". Because this system does not have any relays to ensure both batteries are charged whenever the engine is running the operator must pay attention to the switch selection used. In my experience this is not inconvenient. When starting the engine I select the "Both" position. This provides a generous cranking source for the engine. I leave the switch in this position while underway to allow the engine to charge both batteries. When stopped with the ignition switch off I change the switch position to "Two" or "Off". If I will use any power I select "Two" or if not I use "Off". Before starting again I select "Both". After shutting the engine down for the day I place the switch in the "Off" position. With this system battery "One" serves as a backup battery and will serve to provide sufficient starting power if battery "Two" has become discharged by the house loads. Storing the boat with the batteries turned off helps to ensure that no parasitic loads discharge the batteries. I believe there is much information on this subject in the Reference Section of the site. The information in the Reference Section will be presented in a much more understandable and useful manner. Give it a look. Butch
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jimh |
posted 03-16-2011 10:19 AM ET (US)
See my article in REFERENCE on dual battery configurations at http://continuouswave.com/whaler/reference/dualBattery.html The article only shows simple configurations, and it does not show any ACR or VST wiring. For information on charging a second battery with an auxiliary charging output see |
Jerry Townsend |
posted 03-16-2011 11:36 AM ET (US)
The simplist way is to use a solenoid (common automotive starter solenoid) and actuate the solenoid from the engine's alternator. Connect one of the solenoids main terminals to positive post on the main battery - and the other solenoid terminal to the positive post of the second battery. With only one charging connections/lines from the alternator, install a diode in the charging line to the main battery- so that electricty can only flow to the battery - and not from the battery. Connect the negative terminals of each battery together with a #2 - 4 cable. The solenoid coil is wired using the case as the ground - so connect a small wire from a battery negative post to a mounting screw on the solenoid. This automatically charges both batteries when the engine is operating and isolates the batteries when the engine is not operating. The solenoid is sealed - but mount it in the console anyway. The solenoid might cost $25 +/-. Should the main battery go belly-up - simply remove the cable from the main battery and put on the secondary battery. ---- Jerry/Idaho |
jimh |
posted 03-16-2011 05:31 PM ET (US)
An ACR or VST is a solenoid, it just is a solenoid with some intelligence in its control system that knows when it ought to be closed. |
Jerry Townsend |
posted 03-16-2011 06:22 PM ET (US)
Jim - I might be wrong - but, the only time I see that the contacts should be closed to charge the second battery is when the alternator is operating. Actuating the solenoid from the alternator makes this contact. --- Jerry/Idaho |
Jefecinco |
posted 03-16-2011 06:41 PM ET (US)
Jim, Thanks for the judicious editing. Much improved. Butch |
SJUAE |
posted 03-16-2011 07:44 PM ET (US)
Butch Are you sure about charging both on the simple 4 way switch usually fitted? I thought it was specifically noted in the handbook not to use both for any extended period and the only way to charge both is to use a ACR unit or similar or with an ETEC when fitted with the split charger cable Regards |
Jefecinco |
posted 03-18-2011 09:16 AM ET (US)
Steve, Good question. I have never been told that it is inadvisable to leave the switch in the Both position while running to charge both batteries. I don't recall any handbook on the subject. I have been looking through my "The 12 Volt Doctor's Practical Handbook" but have not found anything on the subject. I've noticed my book is the 1983 edition so perhaps I should invest in a later version. How time does fly. I remember buying this book at Spa Creek Instruments in Annapolis back in the day. I've been using the Both position while underway to charge both batteries on my boats since 1978 without a problem. If it makes a difference, I use matched batteries put into service on the same dates and over the past several years have used AGM batteries. Butch |
Jerry Townsend |
posted 03-18-2011 10:57 AM ET (US)
Butch / Steve - I suspect that it doesn't make much difference - since a battery is a good regulator - it will charge as needed. Think of it this way - with a discharged battery, the voltage will be lower then that from the alternator and current will flow to the battery. When the battery is charged, the voltage difference between the battery and the alternator tends to be very small - which decreases the current flow to the battery. ---- Jerry/Idaho |
jimh |
posted 03-18-2011 11:30 AM ET (US)
Moving an OFF-1-BOTH-2 battery switch to the BOTH position parallels the two batteries. When the solenoid in an ACR closes it parallels the two batteries. There is no difference. An operator who knows when to move the switch to BOTH and when to switch back to isolated batteris can function just like an ACR. An auxiliary charging output does not place the batteries in parallel, |
SJUAE |
posted 03-18-2011 05:51 PM ET (US)
From my BW Manual 2006: "Your 210 Outrage uses a battery selector switch to From the 2008 Manual: "Dual Battery Switch The dual battery selector When the engine is shut down or not providing a Notice how it changes from should to must be switched from the all setting once the engine is running So is BW advice not to be followed ?
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SJUAE |
posted 03-18-2011 06:30 PM ET (US)
Jim You may well be correct re charging in parallel with an ACR unit I recalled some good details by Andygere who uses a BEP switch http://img.photobucket.com/albums/v408/andygere/Whaler%20details/ BEPwiring.jpg http://img.photobucket.com/albums/v408/andygere/Whaler%20details/ IMG_0697.jpg This switch notes emergency parallel so maybe it's not the charging thats the main concern but something else when leaving the switch in the both position. Regards |
Jefecinco |
posted 03-18-2011 06:45 PM ET (US)
Steve, I've never taken delivery of a boat with a dual battery installation. I've always simply added matching batteries and a 1, 2, Both, Off switch in a wiring system very much like the one provided in the reference section for single engine dual battery installations. It is very difficult for me to understand why it would be undesirable to allow battery charging while underway by setting the switch at Both. OTOH, I've been often warned not to change the setting of the switch while the engine is running as that can blow the alternator diodes. FWIW. Butch |
SJUAE |
posted 03-18-2011 08:37 PM ET (US)
Butch I also don't know :) maybe our guru sparkies (Jim/Jerry) can give the answer, all I did was follow the manual. Regards |
deepwater |
posted 03-18-2011 08:49 PM ET (US)
carlo,,It might help if you contact the manufacture of the motor and ask if the alternator is capable of charging 2 batteries,,Pulling more out of any electrical item than it was designed to produce seems to be harmful to the unit causing premature failure,,They built it they should know |
Jefecinco |
posted 03-19-2011 07:22 AM ET (US)
Deep, Carlo has a 150 Verado on his 190 Montauk. No worries on the charging capacity. Butch |
jimh |
posted 03-19-2011 08:33 AM ET (US)
The concern expressed about operating a boat with dual batteries with the batteries wired in parallel (as occurs when you place an OFF-1-BOTH-2 switch to the BOTH position or when the solenoid of an ACR closes) is for a weak or damaged battery to cause harm to the other battery. When you connect two batteries in parallel, the battery with a lower terminal voltage will tend to draw current from the other battery that has a higher terminal voltage. Another concern is for the charger. If both batteries are deeply discharged they will both tend to draw high current from the charging source. Charging two batteries in parallel may overload the charging source. The ACR mitigates these problems because is will not operate the solenoid until the first battery terminal voltage has risen to a point which is typical of a battery with full charge. When an ACR puts batteries in parallel, one of the batteries is already fully charged. If the load of the second battery is too great and causes the terminal voltage of the combined paralleled batteries to fall below a threshold, the ACR will drop the solenoid and open the connection. The ACR has some built-in intelligence, and it knows when to allow the batteries to be in parallel. An operator who moves the OFF-1-BOTH-2 battery switch on his boat to BOTH has placed the two batteries in parallel, and the operator may not be aware of any problems with charging that could result. If both batteries are in good condition, that is, without a shorted cell, and if both are of a similar type and age so that their charging rates are similar, there is likely no great harm to occur from letting them be in parallel while being charged. When there is no charging current available, it is probably not a good idea to keep two batteries wired in parallel. Any load on the batteries will be discharging both batteries. The principal reason to have two batteries is to keep one in reserve in order to be able to re-start the engine. If the battery switch is kept in the BOTH position, one could find themselves with two batteries that were both discharged to the point of being unable to supply current for engine starting. Batteries are not self-aware, and they don't know the difference between being placed in parallel by operating the OFF-1-BOTH-2 switch to the BOTH position or being placed in parallel by the solenoid of an ACR or VST closing. The electrical circuit is the same. The only difference is perhaps a few one-thousandths of an Ohm of resistance increase due to the added wires in the ACR circuit. |
deepwater |
posted 03-19-2011 04:52 PM ET (US)
Thanks Butch. [Odd and incorrect attribute to me of something I did not say has been deleted--jimh] [S]ometimes we ask too much from our electronic gizmos and they over heat or starve for power. |
jimh |
posted 03-19-2011 11:12 PM ET (US)
If anyone is aware of a Mercury VERADO option to provide dual isolated charging outputs, please join our discussion. Otherwise, I think my earlier guess is probably correct. A Mercury VERADO does not have dual isolated battery charging outputs available. |
jimh |
posted 03-20-2011 07:33 AM ET (US)
There is not much worry about the charging output capacity from a VERADO motor. They typically have very strong charging output, and they need it. The battery associated with a VERADO is extremely important because there is no hope at all of the engine operating without a very strong and fully charged battery to support it. The inquiry of Carlo about adding a second battery is really quite a good decision. I am a bit surprised that Boston Whaler sells boats with VERADO motors with only one battery riggeed. |
jimh |
posted 03-20-2011 09:47 AM ET (US)
Carlo--Your inquiry has elicited many responses. You should respond to acknowledge them. |
DeeVee |
posted 03-20-2011 11:59 AM ET (US)
Steve and Jimh, I installed the BEP switch cluster with ACR a few years ago. The switche cluster includes 4 switches- two on/off switches (one for the starting battery and one for the house battery), one emergency parallel switch, and the automatic charging relay. If I remember correctly, the starting battery is always charged first, until it reaches full voltage. Once the starting battery is fully charged, the ACR switches to charge the house battery. I believe the two batteries are never in parallel, unless the emergency parallel switch is thrown. I have also installed an on board battery maintainer/charger that I connect to 110 volt power when at home in the carport. I have been very happy with this configuration. I usually run the VHF, the depthsounder, chartplotter, and stereo all day. Raw water washdown pump, bilge pumps, two electric downriggers, running lights, and miscellaneous deck lights are run intermittently throughout an outing. Knock on wood, so far I have never encountered a lack of 12 volt power. Doug Vazquez |
SJUAE |
posted 03-20-2011 12:44 PM ET (US)
Doug Thanks seems the BEP seems slighly more intelligent than the simple ACR Jim describes. I think your switch must be the same as Andy's (pictures above) Jim thanks for the explanation I'm glad I followed the BW manual :) Is it's possible when having the switch in the both postions that if a device becomes faulty and not only drains the batteries but tries to draw extremly high load and so possible overloading the wiring ? also If the first battery is faulty will it pull all the charging current and deprive the second battery thats good, unless an ACR is fitted ? Regards |
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