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Discussion Starter · #1 ·
Right now I've only got a single in my 18' Weldcraft Renegade. After running my finder and CD player, sometimes I get worried I'm draining the juice. How do you rig two batteries? How do you harness them both?
 

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You need 2 minimum. I just recently had 3 installed for maximum redundancy. I was having problems originally with enough juice and didn't want to worry about getting stranded in the ocean.

I had somebody wire it. I am not an electrician.
You will need a Perko switch for the total connection.

I would do it asap!!
 

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Discussion Starter · #3 ·
I know, I need to get it done, I'm just seeing if I can rig it myself. Hopefully I can get enough insight to do it myself. If not, how much did it cost you RR?
 

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Do a search, this same subject was discussed about a week or so ago.

JK
 

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You can do it yourself, just be warned, that if you make a mistake the cost to repair the damaged gear could easily pass the cost to have someone do the work for you.

There was a great thread on this about 2 weeks ago Also here are 2 links that I found informative.
Electrical 1

Electrical 2

EK
 

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I'd do it A.S.A.P,,,I pulled in a New ThunderJet from the mouth of the Sandy Wednesday
, He had only a single Batt.. Buy a Perko Switch,,,, Rotate running on #1 an then #2....an Never switch to off when running!..Easy to wire also! Jack Glass took his picture while being pulled in mya mule* :grin: ...bet he went out an gota second batt an switch
 

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I'd do it A.S.A.P,,,I pulled in a New ThunderJet from the mouth of the Sandy Wednesday
, He had only a single Batt.. Buy a Perko Switch,,,, Rotate running on #1 an then #2....an Never switch to off when running!..Easy to wire also! Jack Glass took his picture while being pulled in mya mule* :grin: ...bet he went out an gota second batt an switch
 

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It aint rocket science,,,,hook battery 1 to the #1 terminal, hook battery 2 to the #2 terminal on the perko, and hook all of the wires that are going to the original battery to the load terminal on the perko switch. Connect the grounds from battery one to battery two's ground and connect the ground wires from your engine and boat to either battery Use heavy cable for the ground between the batteries and to connect your batteries to the perko.
 

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I was in Fishermans Marine yesterday and saw a book on boat batteries, everything you need to know A-Z. The basics are a battery switch with four positions off, both,1,and 2 a battery combiner or isolator and another battery.
 

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Just an idea - I run an outboard with one batt. But I ALWAYS cary a power-plant with me for emergencies. It's saved my bacon a couple times.
Something like this, anyway.



ORS
 

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I agree that a Perko style switch is the way to go. Slugranch's explanation is all you need. Keep in mind that if you try a battery isolator instead, they introduce a voltage drop, which can be significant under a heavy load, such as cranking over an engine! I alternate my Perko switch between batteries every trip or so. If you don't use the boat for months at a time, you might consider using a home trickle charger that shuts off automatically when the battery is charged. Also, I believe that keeping a battery next to a large heat-conducting mass (like a concrete floor) permanently sucks the life out of 'em. If I pull the batteries for the winter, I insulate them from the garage floor with a slab of wood.

Engineer Dan
 

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_PHN,I'am not sure a battery isolator puts a load on a battery. I load is caused by something using power like a light or depth finder. The isolator I delieve is 2 transistors and a couple of zeinner diodes that sense which battery is lowest and provides a path for the charging voltage to flow. It seems like folks on this board are afraid of battery isolators and the battery switch position that says both.The battery isolator is in use on all autos equipped with 2 batteries,they are always in the both position.

[ 09-28-2003, 11:31 AM: Message edited by: freespool ]
 

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Hi again,

It's not the isolator that loads the battery, but the load that causes the isolator to drop (i.e. "steal") around 1 Volt when there is high current through the load. The most simple isolators are basically a pair of diodes with the anodes connected to each battery's positive terminal and the cathodes connected together at the downstream end, which prevents one bad battery from loading down the whole system (the diodes are semiconductors, passing current only one direction). The diodes are not "perfect" conductors, so they cause a slight difference in voltage potential between the battery and the load (e.g. the engine's starter motor). The voltage difference increases as the load current increases. Cranking an engine can take a lot of current, typically in the range of 50 to 100 Amps, which is when the voltage across the diodes maximizes. When you need every last little bit of engine-cranking power from a battery, only a solid wired connection will get that cold engine to turn over. Not all isolators are made equal, but they all drop at least some voltage in my experience.

If you've ever tried to run a winch through a long cable, it's easy to see how an imperfect conductor (such as the diode in an isolator, or small diameter cable) can steal some of the available power. That's why Slugrancher recommends using heavy cable. It's a must.

(I seriously tried not to be long-winded.)
 

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So if the isolator drops 1 volt what would the amperage drop be? So you have two 800 amp batteries wired in parallel,is the drop significant? And if the isolator is such a draw down on the electrical system,why do all duel battery autos have the isolator installed? I think the pluses far out weigh the minuses on the isolator installation.

[ 09-29-2003, 05:57 PM: Message edited by: freespool ]
 

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Freespool:

Reducing the voltage applied to a fixed load will drop the current proportionally (based on Ohms Law). So, if your starter motor coil presents a load of 0.15 Ohms for example, and your battery voltage is 12 Volts (and the entire 12V makes it to the starter), then the current through the starter motor is 12 divided by 0.15, which is 80 Amps. If the voltage at the starter drops to 11 Volts (due to a low battery, or resistive losses along the way), then the current through the starter will be 11 divided by 0.15, which is only 73.3 Amps. Now, the bigger problem is this: Power = Voltage times Current. The available power to the starter has been reduced from 960 Watts (12 x 80)to about 807 (11 x 73.3) Watts due to a change of only 1 Volt. That's why minimizing connection resistance is so important.

I don't mean to knock all isolators. There are probably some good (and expensive) ones out there that result in very low power loss.

I guess we beat this one to death, huh?
 

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PHN,that's why you have two batteries wired in parellel and the battery switch in both when starting. I'am still not sure how you get a draw in the isolator with those blocking diodes. Aren't they there to prevent current flow in the discharge mode? But during the charge mode they allow current to flow to the low battery?
 
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