Charging boat battery with truck battery

[saildork]

I've read much of the past threads on battery charging, but haven't found this question. Can I use a set of jumpers from my truck's battery to my boat's group-24 marine deep-cycle battery to recharge the boat battery while hauling the boat down the road? I would remove the boat battery from the boat and secure it under the hood of the truck, hooking up the jumpers after starting the truck, and then disconnecting the jumpers when I reach my destination. Would the truck's alternator allow enough current into this 'bank' to charge the deep-cycle battery? Would the difference in the two batteries (starting vs house) be harmful or just not helpful to either/both? Would the length of the jumpers (standard automotive type) cause enough resistance to be a problem?

Pat

 

[Don S/V ILLusion]

It will work but I doubt you want to do this for the following reason - the alternator obviously can't differentiate between the two batteries, one of which is charged and the other isn't. It will sense the avg resulting in over-charging the truck battery and under-charging the deep cycle battery, regardless of how long or short you do it.

 

[fpr]

Don is right... you'll cook the truck battery.

A bigger concern is securing the battery and keeping the jumper cables fastened....

If your truck is like mine the bumps and potholes will/may jar the battery and jumpers loose.
The last thing you want are the cables bouncing & arcing around the engine compartment.

How about disconnecting the truck batt. entirely and rigging the boat battery to the trucks battery cables????
Extend the cables, if necessary, by bolting on extra cables from NAPA, taping the connection with Rescue Tape and secure them in the engine compartment.
That way you can charge the boat batt every time with minimum rigging.

fred

 

[RichBone]

Sure, did all the time with the battery in my camper. But you should use a "battery isolator". It keeps the batteries separated and won't overcharge. There's plenty of info online.
http://www.donrowe.com/battery_isolator/isolator.html
You can also use a solenoid setup.
Much more info can be found in the forums at-
http://www.rv.net/index.cfm
I spent a lot of time there before I got my present boat.
Rich

 

[Don S/V ILLusion]

The use of a battery isolator is wrong in so many ways, it is difficult to find the time to explain them all.
Isolators are diodes which allows them to work in one direction only. When in use, their inherent power loss creates a 0.7 volt voltage drop causing constant under charge. Under-charging is the major cause of battery failure. The only statement in the above post with which I'd agree is "It keeps the batteries separated and won't overcharge."
Isolators are the favorite tool of battery makers since they are the biggest reason people have to buy new batteries.

Regardless of the above, an isolator will not recharge both batteries properly. See my previous post. Neither battery will receive a proper charge.

About the only thing you can assure yourself of if you actually tried rigging up jumper cables is a fire. When you consider how little it costs to buy a small 3 stage charger, one has to ask...

One more note about isolators -
if you want to use this method, get a battery combiner, not an isolator.
A combiner is essentially a relay that functions similar to an isolator but without the voltage drop. Sold by the same people and the same stores.

 

[Rick Webb]

You Need one of These

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200343388_200343388

 

[Stu Jackson]

Sorry, dumb idea

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200343388_200343388

Rick, you evidently didn't read or understand what Don patiently explained.

Buy a good three stage charger for your boat and stop messing around with your truck and maybe "breaking" both batteries and the truck.

What's so hard about doing something right instead of trying to shoehorn something weird?

 

[kloudie1]

My 1978 VW Camper van had the house battery charged by the alternator; factory installed... It had a relay that connected the deep cycle battery to the normal charging system when the ignition was turned on.. It disconnected when the ignition was turned off.. Worked like a champ.. No diodes or anything else.. used a relay like the one that is used to fix the Yanmar starting problem..

 

[Stu Jackson]

Yup, and when a "system" is designed to do just that, it's fine. Trying a Rube Goldberg setup is no way an "engineered solution" like your camper van was. No reason he couldn't do that, but that's not where he was going with this idea.

 

[Rick Webb]

Dumb Idea?

For a Catalina 22 this would be perfectly adequate and fairly inexpensive. The biggest problem is going to be where to mount the second battery. I doubt it is the best solution for charging a battery. Taking it home and plugging it into a battery charger seams a much simpler operation. Perhaps this is not an option for him.

I have operated many vehicles that had multiple radios and lights and this is what was used to provide the power.

 

[Stu Jackson]

It has nothing to do with the type of boat

and ONLY has to do with the batteries.

Catalina 22s need well and properly charged batteries, same as Beneteau 331s. What does the boat have to do with it? Or are you suggesting that Catalina 22s can get away with chronically undercharged batteries? Car alternator regulators are tapering chargers which will undercharge batteries, but be fine for car batteries.

Sure, you may "...have operated many vehicles that had multiple radios and lights and this is what was used to provide the power...", which is exactly the "engineered solution I agreed would work, not some cobbled together malarkey.

 

[Steve Dion]

What is wrong with just charging the batteries with a charger at home? They are not going to discharge enough to worry about in a week or maybe even a month if they are any good to begin with.

 

[Rick Webb]

Here is Another Dumb Idea

I can think of many reasons our freind in Guntersville is unable to take his battery home to charge. Maybe he is in school or the military and lives in the dorm or perhaps he does not want his wife to know he has a sailboat.

Anyway with a regular battery charger plugged into an inverter in his truck he could charge his battery on the way to and the way back from the lake.

For the couple of lights and radio in a Catalina 22 this too should be an adequate solution.

 

[kloudie1]

Not the best of conditions, but won’t harm either battery in the short term.. IF the charging system is in good health.. Think of voltage as “pressure” and current as “flow” .. If two batteries of different pressure (charge states and therefore voltage) are hooked to a system that has unlimited and slightly higher pressure than either battery, the one at lower charge state (pressure) will take most of the current flow.. The other battery being at a higher pressure will not take nearly as much flow of current because the pressures are close together.. as one reaches the pressure of the charge system, the flow to it will decrease.. It will not cook if the other is discharged and taking the current .. The voltage regulator does exactly that, it varies the voltage or pressure that the battery sees.. A check valve (diode) between the batteries is necessary only if they stay hooked together after the source of pressure (alternator) decreases below the pressure in either one. Now I am talking an automotive system, not the sophisticated systems that some folks have on their boats.. The Volkswagen system was only an automatic way to connect and disconnect the “jumper cables” that Pat was talking about.. I read his question as “Can I do this?” I believe that the answer is yes, BUT it is not a really good or optimal solution..

 

[saildork]

Appreciate all the input. I figured there would be a lively discussion since battery issues are one of our favorite topics. (Anybody want to talk about anchoring?:stirthepot

Perhaps a bit more background would be helpful. My boat sits on its trailer at the marina. There is no electricity available for charging the battery while it's there. So, if I'm away from the boat for a while, I take the battery home and keep it on a charger in the garage. I'd like to hook up a good solar system that could recharge it after a weekend on the water, and keep it charged while it sits. And that might be what I should ultimately consider. but for now, I'm looking for simple, low-cost, effective, and safe.

For this discussion, I was thinking of how to charge the battery while enroute from one body of water to another, away from shoreside electricity for extended periods of time. I agree the jumper-cable idea sounds pretty Rube Goldberg and potentially unsafe. So could I install a system similar to what many of you have on your boats for the starter battery and the house bank (in this case, under the hood of the truck)? Would a solar system on the boat be more cost effective and less engineering-intensive? Am I trying to make a mountain out of a mole hill?

 

[Stu Jackson]

KISS. You answered your own question. You CAN hook it up to the truck, but why try to do it under the hood where's there is most likely NO f-ing room? Why not run some wires back either into the cab to into the bed and put your boat battery there? But this requires you to MOVE the boat battery back and forth, right? So, get a small 11 watt solar panel, leave it connected o the BOAT battery left ON the boat during the week and you will have a fully charged battery every weekend. Doh!:dance:

 

[saildork]

Thanks, Stu. Yea you're right. I'm trying to make it too complicated. The solar panel idea makes the most sense, and moving the battery back and forth to the boat is a PITA. Thanks again.

 

[Honeyman]

Go to your local VW dealer and beg them for one of the chargers that most all VWs ship into the US with. The dealer's employees pretty much steal all of them and the owners never see them. Google "VW solar chargers" to see what I mean. Unless you're pumping lead for health reasons, moving batteries around is just "stoopid"!!!

 

[sand sailor]

harbor freight has this http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41144 and it works great on my 2 battery system

 

[Don-MT]

VW Chargers

Go to your local VW dealer and beg them for one of the chargers that most all VWs ship into the US with.

A couple of recommendations for the VW solar chargers; 1)They were meant to be attached to the inside of the windshield via suction cups and 2) some were coupled to the charging system with a VW specific adapter. So, 1) run a bead of silicone caulk around the exposed seams of the charger to prevent moisture from entering the housing, and 2) Change out the VW connector to a power plug (we used to call them “cigarette lighters”) and wire in a power plug to your boat system. I have used mine for 2 years now and haven’t had a bit of trouble. I just plug it in and leave it facing south until I return for the next sail. They have a diode to prevent discharging at night.
Shine On!
Don