Dual Batteries

[troy]

Taken peoples advise and had dual batteries fitted.
Now is there a way you charge them and do you disconnect a terminal while charging.
I have always taken the positive off when not using or charging but i was told it is in your manual to take off the negative.
Any reason for this.
Thanks
Troy

[Dave]

The reason for not taking off the positive cable is that if you do happen to touch an body-earth next to the battery it could possibly cause a spark and the battery could explode. This is not the case with the neg cable, if you do happen to touch the body-earth this will not happen. I was always taught as a mechanic to undo the earth cable of the engine block or body where ever it might be rather than disconnect from the battery. You can still get small sparks when removing/installing either terminal from the battery. This is a bit more important if the battery is in a confined space. Hope this helps.

I fitted an isolator switch for my duel batteries. You can switch from either one to charge or both at once. This is good if you do night fishing, you can flick over to one battery running all the lights etc. leaving the other with full charge for starting.

If you do charge you batteries on a battery charger rather than the boat, definately disconnect the neg lead to charge. Here's a pic of my set up with the switch.

Dave

[troy]

Haines thanks for your reply but i still do not no why you should dissconnect the negative cable.
Troy

[Dave]

It is mainly to protect the alternator and the electrics that are connected to the battery. Like when welding on a vehicle you could get a spike or high current flow through your electrics which could stuff them up. Things like voltage rectifiers in the alternator. The battery charger can do the same thing.

Dave

[gif]

Hainsey - "Body earth" ?

Are you thinking cars?

I believe that metal Boats are not body earthed like cars

and with a fibreglass boat ...?

[seatime]

The procedure I follow with battery leads and chargers is the positive lead is attached first and taken off last from the terminals. This instruction was in the manual for one of these Smart chargers for an AGM battery.
While I'm not entirely certain of the reason for this, the charger becomes live once the battery is connected, lights come on etc, a power spike could damage the charger if the leads were connected incorrectly.
There tends to be less sparking doing this way too. regards

[troy]

Hainsey if you had the positive disconnected and you accidentially connected the charger up the wrong way could any damage be done.
Troy

[marlinqld]

Fit an isolator so you can switch from dual to single when out.

[Dave]

Troy, Yes that is the way for cars. You disconnect the earth lead from the engine block or body. Not always easy to do.Usually car batteries are pretty well ventilated so you can get away with disconecting the earth lead from the battery terminal. I know if you hit the body in the glass boat etc it wont spark, I was pointing this out. That is the way for cars and I just transfer the reasoning to the boat.

If you had the battery disconnected your electrics will be safe and (most - or I know that mine has) of the new chargers have a safety for reverse polarity so that if this happens the charger does not put power to the battery.

Dave

[Dignity]

Dave, was that switch connected to the negative poles - wasn't sure mainly due to the use of green outer casing.

Troy, I always worry about charging the batteries mainly because I had an charging module fitted to an old Suski many years ago. A month later didn't think it was charging and when I went back to the dealer (who now seems to get rave reviews these days) I was told that things such as connecting the battery the wrong way or charging the battery without disconnecting all the terminals would stuff it. Cost me $80 back in the early eighties for the module, cost the dealer lots more in service since then. I disconnect all the terminals. My negative cables are all currently connected together with a bolt. Not the most technological system but all I undo is 1 nut, separate all the cables and as the positive cables are running through a 3 way switch I can easily disconnect them. I do intend to install a switch for the negatives.

BTW I believe the system of disconnecting the negative first on vehicles as Dave mentions was derived from the fact of weilding a spanner connected to the positive terminal and accidentally touching the body of the vehicle which completes a circuit. Also when runnnig anything directly off a battery in a car eg air pump etc the negative ( for a negatively earthed vehicle) it is suggested that you connect to a part of the vehicle away from the battery particularily if the vehicle has just been used. This is because th abattery will be giving off hydrogen and in a confined space the build up is enought to cause an explosion if a spark occurs during this connection. I actually witnessed such an occurrence with a truck driver. I was about 20 m away when it occurred. He an Acco tray top, pulled into the yard, opened the battery compartment pulled off a cable (sorry don't know which one) and the battery exploded. Fortunately there was hose nearby and I had him drowned before he knew what had even happened. The interesting thing is that I would have thought as the batteries were virtually sitting in clear air the gases would have dissipitate so quickly that there wouldn't be enough to even register on a gas detector. It was enough to convince me to never try playing around with a battery if the vehicle (boat ) has just been used or the battery has just been charged.

sam

[blaze]

good policy to always disconnect neg first. Also be aware of the danger of batteries. Lifting a dozer battery out from under the seat with a co worker, he had a six inch shifter in his top pocket witch fell out and caused the battery to explode, took a far hit in the face along with lots of acid. Must look funny with blaze on his knees bside the dozer with head fully immersed in muddy water. Few stitches and eye pads on for about a week due to acid burns.
cheers
blaze

[Fishin_Dan]

The reason that you are supposed to disconnect the negative first is that the "electricity" (for want of a better word) actually goes the other way to what you think (ie -ve sends it out, and +ve receives it). It's all kinda backwards...

So by disconnecting the -ve first, you are in essence disconnecting the power first. And by reconnecting the +ve first, you are actually earthing the battery first.

:D Hurts the brain a little doesn't it

[Dignity]

ouch - where is the ouch smilie when you want one - that theory hurts Dan


sam

[Chimo]

Troy
Do you have your motor hooked to one battery and the rest ie sounder, GPS, lights live bait pump, bilge pump, radios etc connected to the other .

Reason I ask is that I didn't and 2yrs from new I started to loose screen pixels on a Lowrance 2000 Globalmap sounder /GPS.

Thankfully they have a 3 yr warranty and Lowrance replaced the unit at no charge but "strongly recommended" that all non-motor electronics not be connected to the motor battery. The issue that they put to me was that on starting there is a large voltage drop with frequent spikes and large voltage fluctations just after the motor fires.

I had a marine electrician rewire the boat with isolation switches and we added a large, deep cycle "house" battery.

The issue of connecting the two and safe charging has been addressed with an inexpensive but very effective gismo called an "Auto Battery Coupler" (ABC) This works by electrically disconecting the house battery; and everything electrical in my boat not associated with the motor; from the motor battery when I hit the starter and the ABC detects a voltage drop in the circuit.

With the motor operating and the voltage stable and spikes no longer an issue the ABC reconnects and the house battery and charging takes place. I reckon its cheap insurance. It also works at nite etc, initially you can draw on the motor battery for lights and pumps etc as they are connected but once the total voltage drops to a certain point which ensure you can start the motor the ABC disconnects and all current can only come from the house battery.

Has worked a treat for years it also regulates current flow into the house battery when I charge the motor battery in the boat.

The people who sell and set up boat electrics have to work to a cost (cheap) and they may or may not know the long term (two years in my case) ramifications.

Hope this is of interest.

Chimo

[wayne_cook]

chimo I agree

I run one battery for motor & deck wash.

and one for all other gear.

A battery switch but the electronics are connected straight to the second battery.

The only time I run (motor) on second battery is when electronics arn't being used.

As you I learnt the hard way what motor spikes can do to expensive electronics.
The system i use works for me but may be a complicated for novices to wire.

[troy]

Chimo they never told me anything when they installed them.
I contacted them before i charged them and was told to disconnect the battery with the 3 negative wires to which i did but it still sparked.
Also they said to leave both terminals on the second battery after i charged the first as by taking of the 3 negative wires on the first makes it safe.
Do not know why it should spark by taking off these negative wires.
I am pretty dumb.
Troy
ps never charged a battery without taking off a terminal so i hope they are right.
I do have a isolating switch which they told me to turn off.

[ahoj]

Your motor is connected to earth at all times even your leg-- by removing earth from batteries you isolate all earth to all electrical components.. if you remove the active any positive static electricity can and will cause damage to regulator or rectifier or even starter and electronics.... I Have been doing it like that for years and never problems.

Ahoj

[Dignity]

Chimo they never told me anything when they installed them.
I contacted them before i charged them and was told to disconnect the battery with the 3 negative wires to which i did but it still sparked.

Troy, I am not qualified in any way with electrical componentry but this smacks of something that is connected and is still in the ON position. Have a real good look at everything you have connected and make sure that nothing is switched on.

sam

[troy]

Sam are they right by saying that after you have dissconnected the 3 negatives wires from the first battery that you do not have to remove any terminals from the second battery when you put the charger on this battery.
Troy

[Dignity]

Troy, that is what I am reading but as my positive leads go via a switch I simply put it in the off position. As I said all my negatives go to a single conncetion point - I have 5 of them 1 each from the batteries, 1 from the motor, 1 to the bus bar for the electronics and 1 for the electric anchor winch - simply disconnect and everything is isolated. sent you a PM

sam

[flotsom]

hi,

hopefully i can help with all these questions,

1. when you connect a battery and it sparks that meens that something is drawing power from the moment the battery is connected, it could possibly be a GPS aerial in some instances or even a capicitor in one of the radios, one samll spark to excite a capicitor and then no more current draw.

2. in survey it is a requirement to switch both earth and positive leads, it is a overkill, positive leads are enough as once you have removed positive power the battery is not active, zero volts are running through the boat or motor so why the need to remove the earth terminal - none.

3. the best battery charging devise i have seen ever is a BEP VSR readily available from any decent marine shop, check out website, i think it is www.bepmarine.com BLA are the distributor in australia. it will allow duel battery install with one battery kept soley for engine starting and the second battery kept for accessories, the benefit is the 2nd battery will not be drawn upon when starting the motor so your GPS or sounder will not cut out, therefor with voltage spikes that could happen it will not void your warranty on your electronics, if you have ever read your owners manual with your GPS you will see that it says to turn the unit off before starting motor, this is to avoid spikes. when the motor is started and the start battery reaches around 12.8 volts (around that) it will link the 2 batterys and then charge both off the motor alternator. when the motor is switched off the unit will de-link when battery voltage decreases to protect your start battery. when you charge the batterys when you get home (if you like) you can hook charger up to the start battery and it will do the same thing ending up charging both batterys, then complete the cycle, turn the isolater off and never a flat battery. any body in 4x4 world would have seen there models available butt this is smaller, water proof and also around $100 instead of 4x4 version around $400. + isolater switch BEP again for around $50.

hope this makes sence and i can help with any questions or comments.

[Chimo]

Hi Troy

I agree with "Flotsom" and it seems the thread has covered a lot of the subject and then come back to the basics. As Flotsom says if you read the manuals for our instruments earlier than "when all else fails" they basically say what Lowrance told me and thankfully they still honoured the warranty. Turn off GPS etc before starting motor (if on same circuit)
It is much safer to keep motor and instuments separate. The item Flotsom talks of and the Auto Battery Coupler manufactured by an EK Rowe on the Gold Coast do similar things.
Since I now have a digital camera thanks to input from other helpful people on this site I had a go at taking pictures of the wiring diag and the schematics of the ABC that I have now found.
Hope they of some interest. I also have some contact details of Mr Rowe if you want to PM me.

All the best

Chimo

PS Attempt 1 photos too big? Attempt no 2 just over 100kb no go either; more research required?

[Grand_Marlin]

Also an interesting point for you to consider....

All moored boats with a 240 volt battery charger never disconnect any terminals when charging.

They just plug in shore power and the charger is automatically on.

Most of these run a VSR to charge start batteries first (priority battery), then house batteries (secondary).
The VSR, as stated, keeps optimum charge in both batteries, by charging the primary battery first ... then the secondary battery.
It only protects thge electronics "by default" ie it gives priority to start batt for initial charge, effectively isolating the house batt where electronics are run from, on initial start up.

Nearly always the electronics are run off the house batteries, but quite often there are two big start batteries (N150 or N200) that are both high cranking amp start batteries and deep cycle batteries for house use as well. Everything runs off these batteries.

I have even worked on a boat (yacht) that had a supercheap car battery charger connected to the toilet wiring at the other end of the boat, and was charging the batteries through the whole electrical system :-/

This I dont recommend, but the point I am making is ... it worked.

Now, back to the VSR.

Keep in mind that the VSR ony regulates charging, not current draw from the batteries you are using ... in other words, it is only of use to you when you have your motor running. (or a charger connected)

A VSR will not stop you from flattening all your batteries in a twin battery installation.

For this you need the battery isolation switch (batt 1, batt 2, both, off)

The VSR will work well, but it is going to cost you between 150 and 300 bucks depending on what one you need.

You could also just use the battery isolation switch to protect your electronics.
The batt isolation switch is about $40.

How?

Use batt 1 as your dedicated start battery.
Use Batt 2 for your electronics (run 6mm wire from batt to bus bar in cabin)

Always make sure the switch is on batt 1 for starting - this way there can be no spike to batt 2 on start up.
If you feel batt 2 needs some charge, simply switch over to batt 2 on your run out to (or home from) the fishing grounds.

Just remember not to start on batt 2.

This is my recommendation.

Also, you have the added benefit of no sounder interference from charging batt 2 when trolling etc, as it is isolated.

The problems associated with a spike are a concern, but not something that happens very often .... look at how many thousand boats there are on the water with single batts doing everything, as compared to the reports you get of blowing up the sounder when starting boat.....

The VSR will work and work well, provided it is installed properly.

Idealy, you still need the Batt isolation switch.

The batt isolation switch used without the VSR (if you use your head) will still do the job perfectlt.

Cheers

Pete

[Grand_Marlin]

VSR

[Grand_Marlin]

Batt switch