Charging boat batteries while towing

Nwdiver

Nwdiver

Well-known member
Joined
Oct 16, 2020
Messages
264
Fluid Motion Model
C-288 C
Hull Identification Number
FML28C09H222
Vessel Name
Old Bold Diver
Am curious, does anyone charge their boat battery while towing? For longer trips, I would probably have the refrigerator running and possibly the water heater. The refrigerator probably won’t drain the batteries, but the water heater definitely would. If you do charge, is there a standard way to connect to the tow vehicle?
 
I’m not aware of a way to tap into the truck’s charging system to power the boat, but I have an older boat and older truck. Maybe on newer models of both there is that utility.

During a sunny day, I let the solar panel do its magic. It will just about keep up with the refrigerator. If it’s cloudy or dark while I’m towing, I have a Honda 2000W generator (1500W max continuous) that I put in the cockpit and plug it into shore power. That keeps the batteries topped and will power the hot water heater if desired. Actually, a generator is the only reasonable way to power the hot water heater while towing since it is AC powered.
 
Most tow vehicles have a 7-way trailer wiring plug, on the #4 (black) is the 12 volt from the tow vehicle, the #1 (white) is the ground from the tow vehicles. You can wire this in to your battery system and charge your batteries during towing! Most travel trailers and other RV's use this charging system while towing. I use this system during camping with my horse trailer/living courtiers I start the truck and charge the batteries when the solar system is not enough due to weather conditions. Bob
 
That’s what I was thinking of, just not sure of an easy way to get the power into the boat battery. Maybe hook into one of the down rigger connections. I will have to check the fuses in both the truck and boat. Looking for other ideas/options
 
First thought is that trying to use your water heater while towing will be a tremendous drain on your batteries and I doubt that the charge will keep up. The second thought is that from the front of your truck to the back of your boat you have a fairly long distance. There will be quite a bit of resistance developed over that distance. I had the same thoughts as you about charging while driving. I never did it, but if I was, I would have run a large gauge set of wires off the truck battery with a separate connector at the rear of the truck. Then another cable on the trailer that would plug into the new auxiliary truck connector and a run to the back of the trailer with another connector. From there then a length of short cable with a plug at one end to the trailer and at the other end clamps to go onto the battery posts. I found when towing my priority was keeping the refrigerator going without draining the batteries. The solar panel did a pretty good job at that. When I got to a campsite I just plugged in and charged up as one would do on shore power. Hot water once on 110 volts is available pretty quickly and once the water is hot it will stay pretty hot while traveling even when not hooked up to power.
I think before I would try charging from the truck while towing I would add another solar panel and then have a better charge while anchoring out and a pretty good charge while towing.
 
Am looking at adding more solar, yet to be seen if that will be enough here in the PNW. Refrigerator is definitely the priority, hot water is probably a pipe dream, but will experiment with if it is already hot, how much power does it take to maintain temperature. Whatever I end up doing, I have to make sure I don’t end up draining both the truck and the boat. That would pretty much end a vacation
 
Just a side note: most boats with a kicker motor will have the kicker motor charging system tied in to keep the house batteries charged while fishing and using the downriggers. I have a 6 HP Tohatsu and have the charging system tied into the downriver plug, not much of a charge but enough to keep house batteries topped off on those foggy and raining days which is about 90% of the time during fishing!
Also if your boat has the running lights powered from the trailer via a pig tail you already have power from the tow vehicle (but would want to upgrade wire system.
I can power a full size freezer from my truck and have done so on many fishing trips. Bob
 
The scheme to provide DC power from a truck electrical system to charge boat house batteries as described by Mike sounds pretty involved and complicated. Another issue is there is no regulation of the current going to the boat batteries and one doesn’t know how much charge current is being sent to them.

A small generator running in the cockpit while towing is a much more simple solution. AC power goes from the generator to the boat power system and it is operated normally. I constructed a short pigtail that plugs in to one of the standard three-prong plugs of my Honda generator and the other end has a normal twist lock plug for my shore power cord. Honda 2000W generators are available with receptacles that accommodate a shore power cord twist lock connection directly. I bought my Honda generator before owning my R27.

Three of the four times I have “boaterhomed” in my R27, I was parked where AC shore power was not available. Having the Honda generator worked well. Note: I never run the generator while sleeping. In fact, I run it only sparingly while parked and boaterhoming. One of those reasons is to power the AC water heater.
 
A couple of comments based on above replies:
- Casper's idea about the Honda is a good one. I had a Honda on the boat and actually removed it after a few years because
I never used the Honda. Never needed it boaterhoming. Casper needs to stay in higher budget places. :lol:
- I believe that taking power from the truck battery will be regulated since the truck battery is being charged via the regulator. Same as any of the batteries on the boat being charged while the engine is running. I would disconnect when staying overnight or charging from campground shore power.
- Not sure what actual amperage the heater is, take a look in the manual or as a guide look at the breaker amperage and it will be somewhat less. It is an on off function. When the water temperature reaches a low threshold it will go on at full power. When it reaches temperature it will go off. My experience has been after sleeping overnight while anchored I had very very warm water in the morning.
- I would use my money and energy improving the solar system. Just changing the controller can make a difference.
A PWM controller operates at a relatively constant harvesting efficiency regardless of the size of the array
A PWM controller is less expensive that a MPPT, so is a more economical choice for a small system
A MPPT controller is much less efficient in low power applications. Systems 170W or higher tickle the MPPT’s sweet spot

It sounds like the towing experience with the boat is new. So perhaps try it without doing anything. You may find out that doing nothing works well. It did for me and I towed the boat a total of 40,000 miles.
 
I left out an important piece of information: I use the Honda generator only while towing. I never carry the Honda generator on the boat while it is in the water. For generator needs on the boat, I have an onboard Mase 2.7 generator.

Not all boaterhoming is accomplished at RV parks.
 
When we towed our R25, I gave up on the idea of charging from the truck for reasons mentioned earlier. The thin gauge wire to the 7-pin trailer/camper plug passes very little current, especially at those long distances. Back then, before "overlanding" was a thing, I wasn't aware of the DC to DC Charger option. This is now common practice to charge auxilliary batteries for campers, trailers, etc from the truck alternator. Get a good DC-DC charger, heavy gauge wire, Anderson connectors, and fuses or breakers; all appropriately sized for the length and current draw. Lots of youtube videos out there to show how to set this up. It will take a bit of work and money, but if you plan to do a lot of boaterhoming it will be less than the cost of a weeks worth of hotel rooms.
 
Not to make this a conversation about solar capabilities, but in the northwest MPPT is far superior to PWM, due to the high variability of cloud cover, regardless of array size. I'm about to switch my Mornigstar PWM controller out for a Victron 100/30 MPPT smart controller for this reason. I'll eventually get a 200w panel, but I expect i'll get 20-30% more juice from the existing panel with the MPPT controller here in the NW.

knotflying":16xe5q47 said:
A couple of comments based on above replies:
- Casper's idea about the Honda is a good one. I had a Honda on the boat and actually removed it after a few years because
I never used the Honda. Never needed it boaterhoming. Casper needs to stay in higher budget places. :lol:
- I believe that taking power from the truck battery will be regulated since the truck battery is being charged via the regulator. Same as any of the batteries on the boat being charged while the engine is running. I would disconnect when staying overnight or charging from campground shore power.
- Not sure what actual amperage the heater is, take a look in the manual or as a guide look at the breaker amperage and it will be somewhat less. It is an on off function. When the water temperature reaches a low threshold it will go on at full power. When it reaches temperature it will go off. My experience has been after sleeping overnight while anchored I had very very warm water in the morning.
- I would use my money and energy improving the solar system. Just changing the controller can make a difference.
A PWM controller operates at a relatively constant harvesting efficiency regardless of the size of the array
A PWM controller is less expensive that a MPPT, so is a more economical choice for a small system
A MPPT controller is much less efficient in low power applications. Systems 170W or higher tickle the MPPT’s sweet spot

It sounds like the towing experience with the boat is new. So perhaps try it without doing anything. You may find out that doing nothing works well. It did for me and I towed the boat a total of 40,000 miles.
Click to expand...
 
I installed a “Road Toad” system on the truck eight years ago, it works great to keep the boat fridge from discharging the boat batteries too much (three Group 31). It includes a circuit breaker, VSR (disconnects automatically when the truck ignition is OFF), foolproof polarity wiring and microprocessor with LED’s to indicate any possible fault. I connect it down into the chain locker, under the berth onto the helm (House) bus using the boat HD wiring back to the batteries by the transom.

http://www.lslproducts.net/ToadChargePage.html

Works great if you don't have solar or don't want an un-attended Honda generator running in the cockpit on your road trips.

Hope this is helpful.

John
 
Seems like the Road Toad is a good setup and overcomes all the concerns. seems economical as well. The beauty of several minds thinking together.
 
Our Honda generation is a 2200 Companion model that has an app for monitoring. You can even turn it off with the app. Not sure if Bluetooth range would work from the truck reliably, though.

I usually run the water heater overnight before we leave the house, and it’s at least warm when we arrive at our destination. Our first night is usually at a marina, so we re-heat it there when connected to shore power.

Solar keeps up with the the fridge, so we usually arrive with at least 95% SOC.


Sent from my iPad using Tapatalk
 
Thanks for all the ideas. Sounds like I should wait till I have some experience with the boat to see what I need. Am leaning towards the dc to converter.
 
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