Recharging boat battery's while towing....

Ok James and Bob, my younger brother got his laugh of the night I'm sure.... He is quite the Electronics guru, so even though he is my younger brother, I think he is one smart cookie when it comes to anything electrical, so I defer to him. FWIW, I'll just copy and paste his reply (without the laughter that I'm sure was going on as he typed....)

It sounds like your trying to make electricity out of thin air. Let me re confirm your question. You want to be driving down the road with your 12 volt inverter plugged into you boat 12 volt accessory outlet, to power your battery charger, to charge the boat battery's that's currently powering the inverter. This will absolutely not work. First off, there are power losses. Your inverter will use more juice than the battery charger will replace. Second, there would possibly be a ground loop type issue that could damage either the battery charger or inverter. You have to use a separate power source for your inverter. If you plug your inverter into your car accessory outlet, run the battery charger on that to charge your boat battery, that will work as long as you do not have your boat batteries tied/connected in any way to your car/towing electrical system, and the current rating of your accessory outlet is high enough to run your inverter, and the battery charger power requirement does not exceed the output of the inverter.

Example: If your accessory outlet has a 10 amp fuse, it will deliver up to 120 watts of power. If your inverter is 100 watt inverter, the accessory outlet will handle that ok. But, your battery charger will need to require no more than 100 watts of AC power, or the inverter won't be able to handle it.

So, lets look at an example. I have a Sears 12 volt 2 amp battery charger. It's input requires 120 vac at 0.79 amps. That equates to 120 volts X 0.79 amps = 94.8 watts of power (ohms law). Your 100 watt inverter will power my 2 amp battery charger. You have to run it on your car battery. Remember, your drawing just under 10 amps of current off your car battery to produce a measly 2 amps of charge on your boat battery, but that will work. You want to be driving the vehicle though to keep from running the car battery down, as your drawing about 8.3 amps in the above example.

To be clear. You can not run a power inverter on a battery, power a battery charger with that inverter, and then use that battery charger to charge the same battery your running the inverter on. If that was possible, we'd all have free power and no one would need an electric company/utility.

You could also install a battery isolator or simply a disconnect between your tow vehicle's electrical system (battery) and the boat electrical system (battery) that would allow the boat batteries to charge along with the car battery while your driving. Only problem, you'd have to use large gauge wire, because the current flow through the wire would be high if the boat battery is low. Current flow would gradually go down as the battery charged and became matched in charge to the auto battery.

If you had a current limiting device that simply limited the current to say 5 amps, you could use small wire or plug into your accessory outlet. The time required to charge the batteries would be longer.

In your case. Plug the inverter into your car accessory outlet and use a small battery charger on the boat battery. Probably have to run a small extension cord from car inverter to the boat charger. My guess is that your shore powered battery charger is going to put out about 10 amps of current or more, and will require more input power than your inverter can provide. Give me the info on your shore power battery charger and I'll let you know, but I'm guessing you inverter won't power it.

I do have a 1500 watt inverter I use to power my house on batteries when I don't want to run my generator, but it draws about 130 amps of current. I use 3 big ass deep cycle batteries wired in parallel. I'm sure it will run your shore power battery charger. lol
 
My particular wrinkle would be this...I already have a small battery on the trailer tongue to power the EOH brakes if the breakaway switch is activated (in which case a Tom Cat's least concern is whether the fridge stays cold that day). It would be nice to simply tap that +/- to a HD wire down the windlass hole across the berth and plug into the helm 12 lighter socket with fuses. My fridge draws 3A with a 10A fuse. If I forgot to unplug it at night it might drain both the truck batteries and even larger boat House battery, but I bet that would take a couple of days. Or maybe a VSR...hmmm. Any thoughts appreciated.
Cheers!
John
 
John, the break away batteries only have a very small amperage charging circuit. You can use the #4 spade connector on the 7 pin plug, but need to be sure that there is at least #10 wire from the fuse on this circuit and #10 wire into the boat.

Is the 3 amps an average, or when running? Generally the C Dory refers draw 2.5 to 3 amps an hour an average, and draw 5.5 to 6 amps when running. A Group 24 battery (usual battery which is used on most cars and trucks, (except diesels) is 60 to 70 amp hours, and will be at 50% discharge in 10 to 12 hours with 3 amp per hour draw. The group 31 batteries I use for the freezer/refer are 110 amp hours, and I recharge about every 12 hours when using both refer and freezer. If just one alone, then every 24 hours to avoid more than 50% discharge of the battery.

If left to the truck batteries then def a VSR to avoid damage to the truck batteries.

Better to use dedicated wires, directly to the batteries, rather than to a cig plug, because of wire size and current draw. Also the fusing requirement is important.

Colby, get one of the "Kill-a-watt" to measure what a battery charger draws, if it is not on label. It is better to actually measure the draw. I use a 30 amp charger (temp and battery type adjusted) to charge my refer batteries, with the Honda EU 1000 I. The 30 amp charger plus a few other minor accessories, are near what the max capacity of the generator. Battery chargers are generally not particularly efficient, which is one of the reasons not to run them off an inverter--better to have a regulated 12 volt charge directly from the vehicle's alternator.
 
I came across this device which was designed to keep the battery on a "TOAD" or "Dinghy" --vehicle towed behind a RV. It limits the charge to 10 amps, has all of the cable and plugs, easy to install, and disconnects the towing vehicle battery from the "Toad". Would work well for those who do not want to make their own setups with a VSR etc. to charge the battery in their boat while it was towed behind the truck. Cost starts at about $110.

http://www.lslproducts.net/ToadChargePage.html
 
DBBRanger":2ehqkth1 said:
So if the truck is charging at 14.5V, say, and the boat battery is at 12.2V, the drop is 2.3V. If 12 gauge wire has a resistance of .00162 Ohms per foot (total of .175 ohms in your case), then expected current is 2.3V/.175 = 13 amps. That's the most you can expect - I got a lot less. Your alternator will supply what ever is possible (it's not a constant current generator so it will not supply 100 amps unless the resistance allows it).
Click to expand...

I haven't followed this thread too closely, in part because I hope to never need to charge a 16' boat while towing. If it were simple and effective, I might think about it.

What I don't get is how one determines or controls the amount of juice going to the remote batteries. If the batteries are close to dead for some reason, and your vehicle's alternator can put out 100 amps, what limits the amperage to the batteries? 50 amps over 10 AWG is a problem. Over 12 AWG the wire becomes a heating element. Is it simply fused to protect the wire and if the battery truly needs a major recharge the towing charge won't work?

The other issue is voltage loss. Won't running 40 feet of 12 AWG (80' total) at any meaningful amperage result in too much voltage drop? Just 10 amps through 80' of 12 AWG would be about a 15% drop in voltage, maybe more. So at it's best, the 14.5V "charging" system could only ensure that the remote battery doesn't drop below 12.3V. Not really a charging system, but an over-discharge protection system. Or am I missing something about how this can be done with small gauge wire?

I just went though some of this when relocating the batteries on my CD16. Moving the batteries an extra 5 feet meant upgrading to 2 AWG cables, running both grounds to a common buss near the outboard (so that a single ground would never carry the current from both batteries). The calculation had to be done with the starter motor amperage as the biggest draw, so it's different than a trickle charge to a battery. But just running 12 AWG wire from the tow to the "toad" and back seems too easy.

Mark
 
I don't think you are missing anything. Generally many of us "boater camp", using the boat as an RV when on the road. This means that we are not charging the batteries with the boat engine during the day. This would not be an issue, if you were stopping every night at a camp ground where you can plug in a battery charger. But in our, and many others C Dories cases, we stop at WalMarts, camp grounds where there is no power, or even just off the road in national forests or truck stops. The only draw will be a small refer and perhaps some lights (many of us have switched to LED, so the draw is not much). You start the trip with batteries charged. You replace what is used as you go down the road, and what is used overnight.

This is the same way that many RV trailers are rigged, or for that matter, the way that my 42 foot diesel RV is rigged--just a little more robust and taken to an extreme. In the RV the house batteries are 6 golf carts or a usable amount of power of about 330 amp hours (a lot, but we run a residential 22 cu foot refer, as well as 2 satellite TV systems, and a 2500 watt inverter. The "house batteries" are isolated from the chassis batteries, but we have a large frame Leece Neville 200 amp alternator, with regulator, and a 100 amp VSR between the two sets of batteries.

So back to the boat--you will probably wake up in the AM with batteries at about 12.4 volt (we monitor the amps in and out, as well as the voltage of the house batteries) Our Wallas always seems to have enough juice in the batteries to start the stove in the AM.

The VSR does not kick in until the start battery is at 13.7 volts, and cuts out at 12.7 volts. In many ways the resistance of the wire (propeerly fused) is the limiting factor. Most all of the Chevy/GM trucks use a 40 amp "maxi fuse" for this circuit--and often this is not present, but there is a plastic blank. In fact many of the trucks don't even have the wire hooked up, even though the wire is there. Some trucks only have 30 amp fuses--another alternative is to use a 30 amp self resetting (thermal) circuit breaker, if you are building your own unit.

One option is to use the device which I linked to in my prior post, which limits to 10 amps.

You can buy dual output regulators or dual output alternators/with either internal or external circuit breakers. You can use the old fashion way of a resistance coil to limit current (not efficient, --wastes power, generating heat. Another option is to use a power diode. This will drop the voltage by 0.5 to 0.7 volts, and you will probably never fully charge that boat battery, but it does give protection.

I found that with the C Dory 25, and running a 30 amp fuse, right off the battery (with a VSR) of a previous truck, it kept the battery charged all of the way from Pensacola, to Calif, to Washington, to Alaska and then to Powell and back. This was about a month of camping in route in the "Boater Home". I have also used the circuit directly off the start RV of an older RV I had, with #10 wire, and the 30 amp fuse. The length of wire from the trailer hitch to battery and back was % voltage drop with #10 wire. The voltage at the battery in the truck is controlled by the regulator either built into the alternator or external to the alternator. (I have a Scan G gauge or Scan D Guage) on all of my vehicles, so I can monitor the computer voltage on the engine--which is going to be very close to the start battery input voltage. It runs from 12.4 to 14.2 volts on my Yukon.
Lets say 14 volts, so a 10% drop would give you a voltage of 13.4 volts. I haven't gone to the trouble to plug in the actual resistance of AGW #10 wire and Ohms law, but it seems to work well enough to keep the battery charged, and replace the amount used at night--somewhere about 30 to 40 amps.

Having said all of this, you are probably never fully topping off the battery, and so we either stop at Camp grounds once every few days, or if running the boat, at Marinas every week or so, where we can fully top off the battery with the absorption charge going into the float charging phase. (this is the last 20% of the battery charge, whichut is often not fulfilled when just running out boats off the engine alternator, or a truck charging circuit.

There are other ways, but probably not really practical for our boats, and the way we use them. (For example in the distant past I used a "Spa Creek" manual regulator, monitoring the voltage and current flow, with a manual rheostat)
 
Thanks for the insights, Bob, and especially for the TOAD-charge link! That is all I need, at a bargain all-inclusive price. (But if one is $109 and five are $76 each, they aren't selling enough of them). I will replace the boat portion of the wiring harness with Ancor Safety 12v duplex later, but that will be $70 alone.
We will always start off a road trip with boat batteries at 100% topped off, and just want to avoid having the only 12v load underway (the fridge) drop the House battery to <12.2v after a day or couple of long days driving. No one here has been advocating 'recharging' a 'discharged' boat house battery with the tow vehicle on the road, and you cleared that up nicely.
Thanks again,
John
 
I have determined that the PO of my 2012 GMC 2500 had the power brake and aux power connected at the main power panel and fused it. This power runs both to the bumper area AND to a 5th wheel 7-way connector in the bed. I want to install the Aux power to provide 12 volt to the trailer while towing so we can run the reefer.

Couple of clarifications:
- I would think that I need to run both a positive and negative wire from the truck bed to the boat. Some of the posts make it sound like I only need a positive.
- I would fuse the positive at the truck bed plug and at the 12volt power panel behind the healm in the vberth.
-If I connect the power to the power panel directly this would provide power to the entire 12 volt system BUT if the battery selector is set to Off (A B Both Off switch) then no current reaches the battery so no battery charging. I could turn this to A for the house bank and charge them as I travel. Is there anything you need to do to prevent them from "overcharging"? I know my onboard charger controls this but I would be running directly from the truck to 12 volt panel to battery.

I am narrowing my to-do list down BUT keep adding things like this. I am excited to hook this up and have power to the boat while traveling.

Thanks Bob
 
I have determined that the PO of my 2012 GMC 2500 had the power brake and aux power connected at the main power panel and fused it. This power runs both to the bumper area AND to a 5th wheel 7-way connector in the bed. I want to install the Aux power to provide 12 volt to the trailer while towing so we can run the reefer.

Couple of clarifications:
- I would think that I need to run both a positive and negative wire from the truck bed to the boat. Some of the posts make it sound like I only need a positive.
- I would fuse the positive at the truck bed plug and at the 12volt power panel behind the healm in the vberth.
-If I connect the power to the power panel directly this would provide power to the entire 12 volt system BUT if the battery selector is set to Off (A B Both Off switch) then no current reaches the battery so no battery charging. I could turn this to A for the house bank and charge them as I travel. Is there anything you need to do to prevent them from "overcharging"? I know my onboard charger controls this but I would be running directly from the truck to 12 volt panel to battery.

I am narrowing my to-do list down BUT keep adding things like this. I am excited to hook this up and have power to the boat while traveling.

Thanks Bob
 
Yes, you need to run both a positive and negative wire. We put connectors in line, so when the boat is off the trailer it is unplugged. You can use one and coil the charging circuit wire cup in the V berth area, or two, so you disconnect the wire near the console.

Yes, two fuses are proper in this case as you describe.

All of the 3rd part are true. You can put a diode in one, and that would drop the voltage by half a volt--if you are worried about it. I have never had a problem with overcharging. Remember that your outboard is a pretty unsophisticated charging system. Also the 40 feet or so of wire will have a certain amount of resistance. Lets say that you stay overnight in the boat, without 110 V power and want to charge the batteries--leave the house bank switch on for 2 hours. When you do your 2 hour walk around, you can determine if you want to switch that off, and then the refer will be running just off the charging circuit...
 
Bringing this one back. It is a few years older than current but the info seems like it may still be useful, AND, I am going ahead with this project. I'm wondering if anyone has tried this on a Toyota Tundra, and what system they used.

I am all for the KISS principle, and want it a simple as possible. I have no problem with unplugging after traveling and when parking for overnight, then plugging in again in the morning to continue the road travel. I use a CPAP over night, and not much besides that, and would be starting out with fully charged batteries, (Flooded Lead Acid, Interstate Group 29 Marine/RV Deep Cycle), no fridge so about a 5 amp draw over night.

Colby, Chuck, Casey, Bob or anyone else that has a system working, Would you do anything different?

Harvey
SleepyC :moon

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KISS, foolproof microprocessor/VSR and circuit breaker, weather proof connectors and at $104 cheaper than buying all the parts and rolling your own.

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

Truck end hides in the hitch, trailer end installed on helm bus (house battery) and under the berth mattress to close to anchor locker hatch, removeable mid portion from hitch down windlass hole into chain locker. Crack the locker hatch open and connect the middle portion. Secure that to trailer with velcro wraps. Works great and nothing to remember, the microprocessor/VSR does that for me. 2 minutes to connect.

Great find for 1/10 of a boat unit, thanks again Bob!
Cheers!
John[/code]
 
A couple of observations/questions.

The hookup as shown could lead to the tow vehicle battery becoming discharged. It would be better if this system was powered through something switched by the ignition switch.

While I could see it being useful when towing my boat long distances, like when we are using the refrigerator. However, it seems designed to charge the battery of a vehicle towed behind a motor home. How much utility does it really provide? AFAIK, the only thing that would be a demand on a towed vehicle battery might be the brake lights. At least with my vehicles, they can be undriven for at least 3 weeks (often longer) and will start right up without the need to charge the battery. If I was towing a vehicle behind a RV it'd probably be used at least once a week, so keeping the battery up shouldn't be an issue.
 
ssobol":12s4jzlc said:
A couple of observations/questions.

The hookup as shown could lead to the tow vehicle battery becoming discharged. It would be better if this system was powered through something switched by the ignition switch.

While I could see it being useful when towing my boat long distances, like when we are using the refrigerator. However, it seems designed to charge the battery of a vehicle towed behind a motor home. How much utility does it really provide? AFAIK, the only thing that would be a demand on a towed vehicle battery might be the brake lights. At least with my vehicles, they can be undriven for at least 3 weeks (often longer) and will start right up without the need to charge the battery. If I was towing a vehicle behind a RV it'd probably be used at least once a week, so keeping the battery up shouldn't be an issue.
Click to expand...

I don't tow behind an RV, but I just towed my car on a dolly for 700+ miles behind a truck doing a delivery. for much of that tow it was dark. For that time I did keep the parking lights on in the car. did not have remote for turn signals, but the truck and dolly both had them. I'm just a firm believer in being well lit up when on the road in the dark.

I don't think you could leave a vehicle with park lights on for more than a day and expect to be able to start it. My purpose here is not so much towing after dark as it is having my boat batteries charged up so I can use my CPAP, and a few lights at night.

Harvey
SleepyC :moon

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“The kit consists of several components: A Charge Regulator installed in the dinghy vehicle's engine compartment monitors the charging current and motorhome engine voltage, automatically connecting or disconnecting the dinghy battery from the motorhome whenever the motorhome engine is started or shut off.”
No need to worry about connecting to a truck ignition ‘switched’ point, the Charge Regulator figures it out for you.
When I activate my system by connecting the middle section (truck hitch to chain locker), the green LED comes on, but the yellow ‘charging’ LED only comes on when the truck engine is running. Thus the microprocessor in it is acting like a VSR (but is the size of a matchbox). The max output is 10 amps (plenty enough to replace the amps being used by a fridge or CPAP while enroute on the road, but not enough to properly ‘recharge’ the House battery, as Bob pointed out.
The ‘motorhome’ is the tow vehicle, the ‘dinghy’ is the boat House battery (in my case, connected at the helm fusebox bus, not the boat rear battery box, which saves some wiring and fishing through the stbd gunnel).
During install, I foolishly cut the wires with shears and tripped the included breaker. I like that there is built-in protection on both ends and even ‘reverse polarity’ LED warning.
If you ever want to know whether a system is truly idiot-proof, just let me work on it.
I admire Discovery’s system, effective and functional. But I was attracted to the ‘everything included in the box, even tie wraps and cable connector weather covers’ aspect, which probably saved me 10 trips to ACE hardware. My time and trouble is still worth something (though a lot less than when I was working).
I think 4 others should join with Harvey and get 5 systems for $79 each. If anyone can match all the components including a VSR, circuit breaker, 40 ft of 12g wires and polarity connectors etc for $79 then sing out!

Happy Researching!
John
 
Gulfcoastjohn":6n7qw5gi said:
...
I think 4 others should join with Harvey and get 5 systems for $79 each. If anyone can match all the components including a VSR, circuit breaker, 40 ft of 12g wires and polarity connectors etc for $79 then sing out!

Happy Researching!
John
Click to expand...

I'll go for one if some others want to sign up.
 
Harvey, my system is pretty simple. As you know, I have fully electric brakes on my trailer. That means I also have a "break away" battery. That battery is kept charged by an accessory wire inside my trailer harness. I've wired a two way plug into that wiring going to the Break Away battery. Then I have a "2-wire cord" with another two way plug on the end I place up through the Anchor hawser, and the other end has a "cigarette plug" that I plug into my accessory socket at the helm. When I stop at night, I pull that cigarette plug and plug in my converter that my C-Pap is plugged into. That "charging cord" is zip tied to other wiring running down my berth when I'm traveling, and then removed and put away when I'm on the water. I do have a 5 amp fuse at the plug where the cord connects to my Break Away battery wiring. All works well. Colby
 
Just a question: Would a solar panel on the boat with the proper regulator, recharge the boat battery and eliminate this charging via the tow vehicle connection? Plus, you'd have recharging at anchor or during dry storage, too!

Alternately, how about a wind generator and the appropriate controller? Would have to be self limiting in strong winds and on the highway, but could be a fun DIY project with an automotive alternator, controller, a well balanced fan blade, and a custom built frame. (A more difficult set up, for sure!)

Just doing some WASG scheming, which is always free! :lol:

Joe. :teeth :thup
 
I like the idea of Simple (as in KISS) so Colby your system seems really good in that aspect. I talking with the electronics tech that is probably going to be doing the "wiring" He says that going into the Cig plug at the help could over load that, get hot, and make for bad stuff :cigar :cake or somewhere in between. My dig lighter plug is fused with a 10 amp, and that is really what I was looking at doing, and hoping that would work.

Harvey
SleepyC :moon

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