installing second battery

[ian mcconnell]

I want to install a second battery for safety's sake, I have already installed a battery selector which gives the selection for 1 or 2 or both, the question is will the yam's 90hp alternator able to charge both battery's enoth? i would rather 1 battery at full strength than 2 at half capacity.

also i have installed 2 halogen 55w spotlamps for night use, as well as the normal nav lights, smart guages and satnav, will this put too much pressure on the battery

ian

[Cypman]

Lots of questions to answer, it is unlikely that your lights will overcome your alternator capacity, unless you have them on for long periods when running the engine at very low revs. Regarding the recharging of both batteries, you can easily purchase a device that will only charge the "second" battery once the "first" battery has been charged to an acceptable voltage.BEP Marine make such a device, called a Voltage Sensitive Relay (VSR). Blue Sea Systems do an Automatic Charge Relay which does the same thing and I am sure there are plenty of others in the market. Finally, be careful when switching between batteries when the engine is running as Voltage Spikes often damage electronic systems switched on at the time!!!

[ian mcconnell]

Thanks cypman, good advise

But for any electronic buffs out there, what i am trying to avoid is spending any additional funds.

With the alternator charging both batterys and the selecter set to both batterys, will it charge both equally and then when one is full will it revert to putting all its efforts to the second!!
I know you can buy fancy gismos to regulate power, but logic says it should do this anyway.

[bedajim]

Hi

Have a look here it may help

www.tb-training.co.uk/cover.html

James

[Poly]

Originally Posted by ian mcconnell

I want to install a second battery for safety's sake, I have already installed a battery selector which gives the selection for 1 or 2 or both, the question is will the yam's 90hp alternator able to charge both battery's enoth? i would rather 1 battery at full strength than 2 at half capacity.

also i have installed 2 halogen 55w spotlamps for night use, as well as the normal nav lights, smart guages and satnav, will this put too much pressure on the battery

ian

Ian - depending upon the exact spec of your engine, the alternator might be putting out upto 25 Amps at full throttle. Your spots are going to need about 9 Amps to run, the smart gauges and sat nav etc shouldn't need too much power (say 2-3 amps total). Presumably you have a vhf too (when its not transmitting it won't use much). the power of your nav lights will affect consumption - but say they are 4 Amps then you still have some spare at WIDE OPEN THROTTLE. i.e. you will be topping up the battery.

Both batteries will essentially be charged equally when set to the both position (assuming they are of equal capacity and "discharge" etc.) I think it is normal for people to start the engine on battery 1, run on that for a short time to recharge the power consumed during start up and then switch to "both".

If I was you I wouldn't run the spots for any length of time with the engine off. If you do (or probably if you run anything with the engine off for any period - switch to battery 2).

Your unknown is if with all the gear on and the engine at tick over if the alternator can deliver the required power.

[jyasaki]

Personally, I disagree with Polwart's suggestion (no offense intended.)

You should get in the habit of switching between Batt1 and Batt2 to keep them charged (some folks here use 1 for a trip out, 2 for the trip back. I just switch whenever I think about it.) Either that or get a battery combiner (sits between the batteries and allows a charge through when battery 2 is lower than 1.)

Here's the problems with the "Both" setting:

1) The batteries will try to equalize upon switching to Both. Should you run one battery way down, the amount of current that will be pushed through the cabling could be pretty tremendous. You could also end up with 2 batteries that won't start the motor(s), rather than just one.

2) Running on Both to charge will end up with both batteries being charged to the max voltage of the weakest battery. Should that weak battery be extremely weak, well... (this ignores the fact that a weak battery will *usually* take full voltage, but fall off more rapidly than a good battery. Shorted cells, however, will keep the overall voltage fairly low.)

3) Running on Both makes it much more likely that you will forget to switch to a single battery when sitting on the hook or whatever.

All of the above assumes you are wired up as 2 starting batteries, for redundancy, and not trying to separate house functions and starting functions, though as far as I am aware, the points would still remain valid.

jky

[Pete7]

Ian, you don't have alot of room on an Avon 5.4, and if your not careful this could get expensive or complicated. Why do you want to have a second battery? safety. Have you tried starting a 90 hp with a pull cord? asuming the engine is warm and been run recently its actually quite easy, honestly. On more than one occasion the dive club 85hp Yam has been stated by hand from cold when we left the keys in the club house

If your worried then one good quality battery would be a much simpler answer topped up at home with a charger occasionally. If you must have the second battery and anyone with a fuel injected outboard should consider it, then how about using a changeover switch in the wiring but always using the one battery. Second battery gets a monthly top up at home from a car charger.

Just some thoughts, but do give the pull starting a try, you will be pleasantly surprised
Pete

[Poly]

Originally Posted by jyasaki

Personally, I disagree with Polwart's suggestion (no offense intended.)

None taken. I only have one (very small) battery - on my own boat - I was referring to my understanding of how it is normally done on other peoples boats I have been on.

[ian mcconnell]

Thanks guys

good advise, I also have used the boat on the river and experienced a flat battery after a prolonged 5 day camping trip (obviously using at just above tickover).
As i have fitted a large console capable of taking a second battery, why not!!

I will go with the use 1 battery out and the other battery in, seems a safe bet

[al40]

This is a very common situation on yachts where there is an Engine start battery and then one or more domestic batteries to run the electronics, lights etc (physically seperated). This always ensures you have a good battery for engine starting if you manage to flatten the other one by leaving lights on etc!
If you do opt for a dedicated start battery and house battery then there
are various ways of charging both simultaneously (as mentioned in various other posts above) including the smart chargers, relays etc etc. Depends how much you want to spend and how much technology you want to throw at it!

Linking a flat battery and a fully charged one will not be as efficient as charging the flat one (full one will tend to pull voltage up a bit so current will drop), but it does work OK. I've used a boat for many years that has 3 batteries on a common "bus" with isolator switches on each battery. You can watch the voltmeter when switching the batteries in and out. If one is particularly flat then all the others can be turned off to maximise charge to the flat battery.

Batteries also act as fantastic surge supression so there shouldn't be any issue in switching a 2nd battery on whilst running electronics etc. What you cannot and must not do is turn off both batteries (even momentarily) whilst engine is running... The alternator produces rectified DC but it's a nasty waveform that the battery supresses. This is a good way to fry things as the voltage will also go sky high (although electronics SHOULD be designed to cope with this, I wouldn't take any chances). You may have seen people do this on cars - ie start a car on one battery then disconnect it and re-connect the cars own flat battery - great way of killing the ECU and all other electronics.

[codprawn]

Talking of twin batteries I undertsnad they are required for MCA coding - but do they actually specify the size? I have a huger battery box - can I just stick 2 smaller batteries in there???

[jyasaki]

Originally Posted by al40

What you cannot and must not do is turn off both batteries (even momentarily) whilst engine is running... The alternator produces rectified DC but it's a nasty waveform that the battery supresses.

Very true.

Be aware, however, that some engines have a spare wire in the harness for a "field disconnect", which essentially kills the alternator output while active. Marrying that with an appropriate battery switch will allow you to turn both batteries off while the motor is running (but not for long; no DC output, no power for the motor.) Intended, I believe, for switching through settings (i.e. from "1" through "off" to "2" for example.

I believe my F115 lacks this, but many motors do incorporate it. Would be a good thing to utilize, even if your switch is configured to avoid it, just in case some curious passenger decides to play.

jky

[al40]

Originally Posted by jyasaki

Very true.

Be aware, however, that some engines have a spare wire in the harness for a "field disconnect", which essentially kills the alternator output while active. Marrying that with an appropriate battery switch will allow you to turn both batteries off while the motor is running (but not for long; no DC output, no power for the motor.) Intended, I believe, for switching through settings (i.e. from "1" through "off" to "2" for example.

jky

Interesting! I assume that's where the regulator will be connected. I guess that some engines will disable the alternator via field coils when starter is spinning to reduce engine load. I just know if I connected a switch to that wire I'd forget to re-enable it sooner or later :-(