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Author Topic:   Vehicle to Boat Charging System
Nauti Tauk posted 01-20-2008 09:24 AM ET (US)   Profile for Nauti Tauk   Send Email to Nauti Tauk  
Has anyone fabricated a charging system for the tow vehicle to charge the trolling battery in the boat? I know travel trailers have a setup to do this. Stay-n-Charge makes a unit but it seems expensive for what it is. Seems like a battery isolator and some wire to build a harness of some sort would be all it would take. Not being an electrical guru I don't know what parts would make this work. In Georgia the storage yard doesn't have 110-VAC available for recharging the batteries and it's a pain to take the trolling battery out, lug home, and charge after a day on the lake. Can anybody shed some light on this? Thanks.
tmann45 posted 01-20-2008 09:59 AM ET (US)     Profile for tmann45  Send Email to tmann45     
Yes, you can do this. A battery combiner would be a better choice rather than a isolator. However, I hope you have a few (4-6) hours drive between launch and storage, otherwise your battery will not get much charge. Also, a AGM bettery will take a much faster charge than a flooded battery.
jimh posted 01-20-2008 06:21 PM ET (US)     Profile for jimh  Send Email to jimh     
The best approach to the solution of this problem is to design a DC-to-DC convertor which will be installed in the boat's charging system and can accept a nominal 12-volt input. This unit will handle step-up of the input voltage to the proper level for charging the boat batteries. Then it becomes a simple matter of connecting this DC-to-DC convertor to the vehicle's 12-volt system while driving.

A commercial solution is available. I don't recall the vendor's name.

where2 posted 01-20-2008 08:27 PM ET (US)     Profile for where2  Send Email to where2     
To charge a 24v or 36v trolling battery setup from the tow vehicle, you need a "Stealth 1" charger. Input 12v DC, Output 24V DC or 36v DC.
jmorgan40 posted 01-20-2008 09:51 PM ET (US)     Profile for jmorgan40  Send Email to jmorgan40     
I have the Stealth 1 Pro Pack on my Outrage. You can also set it up to charge from the tow vehicle. I have had the Stealth system in my outrage for over 3 years now and have never had the batteries go low. The Stay N' Charge system is actually a little less money at $219 but I can not vouch for how it works. The DC unit of the stealth runs about $299. The complete Stealth system runs about $600.

Another option for you may be a small solar panel mounted outside your covered stall with a trickle charger.

On a side note, are you in Georgia or did you go back to FLA?

jimh posted 01-21-2008 09:27 AM ET (US)     Profile for jimh  Send Email to jimh     
While this is a bit of a kludge in terms of a system design, if your truck is one of those newer models which feature a 120-VAC outlet powered by an inverter, just get a regular 120-VAC battery charger, install it in the boat, and when towing on the trailer, plug the battery charger into the outlet in the truck.

A system like that would cost about $100 (for the standard charger) and a few buck for an extension cord to run from the boat to the truck. Of course, it might cost $45,000 for the new truck.

jimh posted 01-21-2008 12:35 PM ET (US)     Profile for jimh  Send Email to jimh     
An alternative approach, for those of us whose trucks do not have an integrated 120-VAC power source: Get a 12-VDC to 120-VAC inverter. Install this device in your truck. Then use the system design I describe above. I think the total cost will still be moderate. You can probably install a 12-VDC to 120-VAC inverter in your truck or car for $300. It only has to have enough power to run the battery charger in the boat.

The drawback to this system is that it is probably not the most energy efficient. However, it offers some advantages:

--can use boat charger at dock with 120-VAC power
--can use car inverter to power other devices besides boat charger

jmorgan40 posted 01-21-2008 01:29 PM ET (US)     Profile for jmorgan40  Send Email to jmorgan40     
You are truely an idea man! Great idea. About the same cost as the stealth system.
jimh posted 01-21-2008 01:51 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a device for the vehicle end of the system:

This inverter retails for about $350. [I found it for as low as $220 at some on-line sellers. A lower power version sells for under $200.] It ought to be able to run most battery chargers.

For the boat end of the system, you choose a 120-VAC battery charger appropriate for your vessel.

where2 posted 01-21-2008 11:16 PM ET (US)     Profile for where2  Send Email to where2     
Did I mention that the stealth 1 will charge the trolling motor's batteries off your main boat electrical system before you even get back to the trailer? If you fire up your main engine and it's starting battery gets back to healthy voltage levels, the stealth 1 will begin charging the trolling motor bank.
where2 posted 01-21-2008 11:26 PM ET (US)     Profile for where2  Send Email to where2     
Since we're discussing the potential use of an inverter, an extension cord, and a boat trailer, let us not forget that national electrical codes for 120v AC require use of a ground fault circuit interrupter in "wet" locations. Is that $45k new truck equipped with GFCI outlets? The inverter linked above appears to have non-GFCI outlets. I see no mention in the specifications of it being GFCI protected.

User beware when dealing with 120v AC in the presence of water. The voltage won't kill you, the current could.

jimh posted 01-21-2008 11:43 PM ET (US)     Profile for jimh  Send Email to jimh     
Good point about the Ground Fault Interrupter on the 120-VAC outlet. I bet the OEM inverter installations on the new trucks do have GFI-protected outlets.

I would run the power cable from the boat to the car or truck, and have the 120-VAC outlet located in the interior of the vehicle. It would be out of the weather that way.

On my boat I already have a permanently mounted 120-VAC battery charger on the boat. I would just have to run an extension cord from the charger to the vehicle.

I don't really know if there are any vehicle electrical codes about connecting a trailer to your vehicle and running 120-VAC between them. There probably are prohibitions against it--it could be rather dangerous.

On the other hand, people plug their boat into 120-VAC at a dock in saltwater! I think there is more danger in that than having your boat plugged into 120-VAC while on the trailer and on dry land.

If it starts to rain and pour while you are driving, you could always pull the plug on the charger at the vehicle.

The specifications on the TRIPP-LITE inverter claim it is 90- to 95-percent efficient. That is not much of a loss. I don't think a DC-to-DC convertor is going to be much more efficient, and if it were, it would only be a couple of percent more. It is not like you are throwing away a ton of efficiency with the 12-VDC to 120-VAC back to 12-VDC design.

Tom Hemphill posted 01-22-2008 06:26 PM ET (US)     Profile for Tom Hemphill    
The specifications of that example Tripp Lite inverter states the required input as follows: "Full continuous load - 127A at 12V DC." Evaluate the output of your vehicle's alternator and consider the load already upon it before you head down this path.
jimh posted 01-22-2008 08:23 PM ET (US)     Profile for jimh  Send Email to jimh     
The inverter draws current from the battery in proportion to the current needed to power the 120-VAC device connected. Anyone who understands the most basic elements of electricity knows that the inverter does not draw 127-Amperes unless it needs that much current to supply power to the load. The load can be as high as several thousand watts.

If we allow that both conversion devices (the inverter and the charger) will be 90-percent efficient, then the overall efficiency will be 81-percent efficient.

The implication is that if the inverter draws 127-Amperes of DC current at 12.0-volts, then the charger will be able to deliver about 90-Amperes of current at 13.6-volts. Of course, you would need a charger that could deliver 90-Amperes.

If you have a charger that delivers 5.0-Amperes to the battery, the load on the car battery will be about 6 to 7-amperes. This is calculated at 81-percent efficiency and a slight boost to the voltage from the vehicle battery (nominally 12-volts) to the boat battery charging voltage (nominally 13.6-volts).

The current drawn from the vehicle battery is not particularly greater than would be drawn if a direct DC-to-DC converter (such as the Stealth Charger appears to be) were used. I don't know what the actual efficiency of that device is, but it ought to be at least 90-percent efficient.

The car inverter and boat AC charger solution that I have described here really is a quite workable solution, and, as I mentioned above, this solution provides two very significant benefits.

By using a standard 120-VAC charger in the boat, you get the option of using this charger any time 120-VAC is available. That could be at the dock, in your driveway, at a storage shed, and so on. If you use a dedicated DC-to-DC converter (such as the Stealth Charger) you loose all of those options. The system only works when you connect another 12-VDC source, such as your vehicle battery.

By installing a 12-VDC to 120-VAC inverter in your car, you get the option of running any 120-VAC device you wish from its power outlet. You can plug in your cellular telephone charger, your laptop computer charger, a blender, a drill motor--really almost anything you wish. This makes the cost of the inverted spread over many uses, not just dedicated to charging the boat battery.

If the car inverter is located a long distance from the car battery, rather large wire will have to be used. It would be nice if we could locate the inverter near the battery to minimize the distance and the wire size needed.

Actually, now that I have dreamed up this configuration, I may install an inverter in my truck just for fun. As I said, you can get a smaller one, about 700-Watts rating, for under $100. This will provide around 50-Amperes of battery charging, which is probably far more than you can use unless you have a very big charger installation in the boat. This device would be suitable for my boat, where I have just a dual 5-Ampere charger.

The bottom line is that using my approach you can accomplish the vehicle charger system for about $200 (for the inverter and the charger) and a few dollars more for the extension cord ($15) and the heavy wiring to connect the inverter to the car battery ($50). So for less than $300 you get a vehicle charging system which is much more flexible than a dedicated DC-to-DC system like the Stealth Charger.

jimh posted 02-04-2008 10:42 PM ET (US)     Profile for jimh  Send Email to jimh     
When figuring the size of the inverter needed, I recommend you allow ample headroom. If the battery charger says it needs 550-watts, I would figure on an inverter with at least 1,000-watts.

The output of the inverter can be either "pure sine wave" or otherwise. I have not actually experimented with either kind of inverter. The "pure sine wave" inverters cost quite a bit more, but they have cleaner power output. However, this may not be necessary just to power a battery charger. If you were running an audio amplifier it might be better to get a pure sine wave inverter.

The easiest way to install the inverter would be in the engine compartment,

--there is room
--the inverter is rated for the heat
--the inverter can tolerate the environment, which might be wet sometimes
--the inverter can be mounted properly

If the engine compartment is not a good location for your installation, the closer to the battery the better. Perhaps under the dashboard in the passenger compartment.

You have to run the battery-to-inverter wiring as directly as possible. If
the wiring passes through the firewall, you really should fuse it close to
the battery.

if you run the wire under the vehicle chassis, you may have to shield it with some protective covering. A lot of the battery cable insulation may not be up
to the task of surviving under the chassis.

Installing in the rear of the truck or in the trunk is a good idea, but you will need to use some large cable. On most of the manufacturer websites they have a calculator to help determine the wire size. Bigger is better, but more expensive. You definitely need to fuse a circuit like that, and put the fuse at the battery.

At the moment we are in winter lay-up with both the boat and the truck that tows it around, so I am not actively working on a project like this. If others try this approach, let us know how it works out for you.

One thing to consider is the 120-VAC connection between the vehicle and the boat trailer. For safety reasons you probably need a break-away type of connection, but at the same time you may need a bit of weather-proofing to keep out any water splashing up from the road. This may be the weak point of the design, and perhaps it will need some further researching.

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