Type and size of batteries for dual system

Chris · 14 January 2007, 21:59

I am going to install a new main battery and a second one and wanted to know what would be suitable.....

The main battery would be for engine cranking only and would need to start a 90HP 2 stroke outboard.

The second battery would be primarily for running the electronics (GPS/Sonar, NAV lights, VHF, Bilgepump, accessory socket) and should the main battery bit a little low this battery could be tied in to give a boost using one of these...

http://www.power-store.com/view-item...d=1153&id=198&

I am short on space and do not want to add loads of weight so my thinking is as one battery is for electronics only (unless it is being tied in to boost the main battery) can it not be smaller?

Likewise if the main battery is for cranking only and no electronics it presumably does not need to be so big either?

Chris

Aidan · 14 January 2007, 22:32

Hi Chris,

Just wondering why you need a 2nd battery. i had thought about this two and over the years of sodden batteries and shagged engines, nearly everything let me down from time to time, However that was half the fun (until out at sea). Having thought about this and given power and stuff is my backround, I figured that a High Torque Out Battery from Good supplier such as Lucas or Bosch for Marine use is best.
All you should need is one of these but that depends on the use ( demand and recharge rate and regularity of charging).

In a nut shell I believe that unlss one is expecting much overnight use a 2nd battery is of minor use on any engine with a low usage and recharge rate.
It is usual for Yachts to have these where there can be extended use on Battery without Engine power.
You will need a Battery Switch (relay/diodes etc) and correct fitting (including "Tinning or soldering on Terminals" not just Crimping.

Have you thought of one of these Mobile Hot Start Units. Lidl Ireland)have them on offer at the moment at €38. They are a must on a boat and may well do away with the need for a scond battery on anything but the most useless of Engines. You will always know that they are fully charged when arriving to your boat.
Itis also very useful as a separate power source and Light Source. Plus do not forget that you can use it to lift your engine up or down if the Power trim and Tilt does not work...

al40 · 14 January 2007, 22:56

I'd also vote for a single battery. Unless you are running instruments for a long time without the engine running, you'd have to work pretty hard to flatten a battery to the point where it would not start the engine (typical cranking current for small-mid outboards is a lot less than a car for example - my 50HP has 40amp inline fuse for engine start). I guess one good case for 2nd battery would be where the bilge pump was running unattended.

When I was investigating this, a deep cycle 80Ah leisure battery seemed a good compromise.

Standard lead acid batteries don't like being discharged down to low level (even 50%) and this will damage them over a period of time. If you are going to a 2 battery installation, the service battery (electronics etc) should definately be deep cycle. Reason I mention that is deep cycle batteries are typically quite big - I think the smallest is 70-80ah. It may be you could have a small car battery for engine start and deep cycle for instruments.

If you were concerned about battery useage, you can get good electroic battery computers that can estimate remaining charge and tell you when you should re-start engine to charge the battery.

jwalker · 14 January 2007, 23:08

2 x 50Ahr will be fine. But I'd do it differently. Use just one battery for both cranking and all electronics. Connect the second battery through a battery isolating switch but wire a chunky schottky diode across the switch terminals in the direction of the charge current. This way you'll always have an almost fully charged battery as a backup.

Aidan · 14 January 2007, 23:48

Quote:

Originally Posted by jwalker

2 x 50Ahr will be fine. But I'd do it differently. Use just one battery for both cranking and all electronics. Connect the second battery through a battery isolating switch but wire a chunky schottky diode across the switch terminals in the direction of the charge current. This way you'll always have an almost fully charged battery as a backup.

Hi J Walker, well done, I have not heard of the Schottky diode for 20 odd years, I had tocheck it up on http://en.wikipedia.org/wiki/Schottky_diode.

Yeah have to agree. What do you think of the idea of a Power pack. I expect to get one at Aldi Ireland special offer this thursday for €40.
They are most useful and can be used to ballast bow. I would be probably better of buying a Bosch one. DOnt know what it is bit Bosch always seems to work better.

al40 · 15 January 2007, 00:07

Quote:

Originally Posted by jwalker

2 x 50Ahr will be fine. But I'd do it differently. Use just one battery for both cranking and all electronics. Connect the second battery through a battery isolating switch but wire a chunky schottky diode across the switch terminals in the direction of the charge current. This way you'll always have an almost fully charged battery as a backup.

As you mention, the blocking diode will cause the 2nd battery to be "almost" charged. With lead acid batteries, does that not cause a problem with sulphanation? Generally the alternator regulator will top out at approx 14.4V to prevent boiling the battery. With the blocking diode in the way, with a 0.4 to 0.7V drop over the diode (depending on diode and current), the battery will potentially never enter the absorbtion phase of charging so plates may suplhanate. This will kill the battery pretty quickly! (Diode will also get hot)

A better alternative could be a split charging relay which connects the 2nd battery when engine is running. In an ideal world it would be a split charge cct so each battery was individially monitored but that's probably overkill and expensive.

Would still recommend a deep cycle batt if it's going to be discharged over a period of a days fishing for example without the engine running.

Rogue Wave · 15 January 2007, 00:13

http://global.exide.com/exideGlobalW...n_maxxima_page

best batteries I have come accross.

It is a requrement when coding a boat to have a twin battery set up, I think it's a very good practice to have twin batteries. Having a back up at sea is always good! I don't reckon the power packs much and I certainly wouldn't take one to Sea instead of a proper backup!

If you don't want to splash the cash for the batts above then deep cycle leisure batteries work pretty well, 85 amp would do you and you can get a pair for 70 quid in towsure

al40 · 15 January 2007, 00:38

Quote:

Originally Posted by Rogue Wave

I think it's a very good practice to have twin batteries. Having a back up at sea is always good! I don't reckon the power packs much and I certainly wouldn't take one to Sea instead of a proper backup!

If you don't want to splash the cash for the batts above then deep cycle leisure batteries work pretty well, 85 amp would do you and you can get a pair for 70 quid in towsure

Yes I absolutely agree twin batts is best scenario. I guess my earlier comment re single was one good sized marine battery is possibly better than 2 small car batteries. I was assuming that short of space meant not enough room for 2 leisure sized batts (Chris, how much space do you have?)

On coded RIB's do you have electronc charge distribution to handle both batt's or are they just linked with a switch?

Rogue Wave · 15 January 2007, 00:55

Cool,
As far as I know there is no spec that says you have to have a split charging system, I don't see it as a bad thing though, but I kep it simple and use the selector switch to pick which batery to charge.

re no having enough space, you could always buy a big sturdy toolbax and fit the batts in that and then fit that to your boat !

like this one

http://news.thomasnet.com/fullstory/31410/1424

jwalker · 15 January 2007, 02:03

Quote:

Originally Posted by al40

... With lead acid batteries, does that not cause a problem with sulphanation?

No.

Quote:

Generally the alternator regulator will top out at approx 14.4V to prevent boiling the battery. With the blocking diode in the way, with a 0.4 to 0.7V drop over the diode (depending on diode and current), the battery will potentially never enter the absorbtion phase of charging so plates may suplhanate. This will kill the battery pretty quickly!

No. The normal charge voltage provided by a regulator is 13.7 - 14.2v. In practice, I've found them to usually give close to the maximum. The schottky diode will give a voltage drop of about 0.4v so this is within range.
I've run this system for many years and the main battery has been the one to fail first.

Quote:

A better alternative could be a split charging relay which connects the 2nd battery when engine is running. In an ideal world it would be a split charge cct so each battery was individially monitored but that's probably overkill and expensive.

KISS.

Pete7 · 15 January 2007, 09:09

Quote:

Originally Posted by jwalker

KISS.

Chris, don't forget your outboard can be started by hand, particularly if the engine is already warm. That little piece of rope could be very useful in an emergency.

Pete

Rogue Wave · 15 January 2007, 12:04

Hi

I just use the selector switch to charge the batteries, I don't like electronics on a rib much and don't put uneccesary stuff on!

Thde coding practice doesn't require you to have a split charging system as such (as far as I know)

I have just realised however there is an alternative method of starting for Chris see here http://rib.net/forum/newreply.php?do=newreply&p=181962

Cookee · 15 January 2007, 13:08

Had a long chat with Vicky at Merlin Equipment - we already use them for a number of products, she said that the Odyssey batteries are the dogs danglies and are tiny in size for their capacity. Allegedly better than the Optimas we have been using until now!

www.merlinequipment.com or 01202 697679 ask for Vicky Baker.

Chris · 15 January 2007, 19:20

Cookee,

So which Odyssey battery would be suitable for cranking a 90HP outboard?

Chris

al40 · 15 January 2007, 19:50

Quote:

Originally Posted by jwalker

No.
No. The normal charge voltage provided by a regulator is 13.7 - 14.2v. In practice, I've found them to usually give close to the maximum. The schottky diode will give a voltage drop of about 0.4v so this is within range.
I've run this system for many years and the main battery has been the one to fail first.

KISS.

Yes......

Most alternators will output pretty close to 14.3 or 14.4V when battery is fully charged. In any case, even with best case alternator output of 14.4 and diode drop of 0.4 (ignoring any drop in cabling) the max you will get accross the 2nd battery is 14.0V - and this would only be when main battery had stopped pulling current from bulk charge stage.

Lead acid batteries are really fussy about charge voltage. I suspect if you discharged your 2nd battery (one being charged via diode) on a regular basis (to a good percentage, ie 50%), it's capacity will be very quickly reduced by charging in this way as it would never get to absorbtion stage and would not get fully charged. For a backup it's probably fine but if I was using a service battery I'd want it linked direct to the main battery with a switch or split charge relay.

Batteries WILL suplhanate if not allowed to charge properly. If the maximum charge voltage ever applied is 13.8V and the battery is discharged, then sulphanation will occur.

You should be able to find links about charge graphs online. I pulled a few of these a couple of years back when I was looking at building a smart charger

Stage 1 - bulk charge (up to 80% of charge) - battery takes as much current as alternator will provide. When output voltage gets to 14.2 to 14.3 V move to stage 2

Stage 2 - absorption phase - 80-100% charge. Battery voltage is maintained at at constant voltage (approx 14.3V) until battery is fully charged.

Stage 3 - float / trickle. significantly lower voltage (13.4 to 13.8V) to keep battery fully charged.

So, if you are only ever applting 13.8v, you will not correctly charge your battery and it will loose capacity and die early.

(I trust the KISS was not aimed at me - partic the stupid part :-) ) Simplicity is fine but it also has to work. I use a good old fashioned switch to swap batteries on previous boats. No voltage drop, no electronics, complete control)

al40 · 15 January 2007, 19:58

Just found a link to battery charging.

http://www.emarineinc.com/articles/b..._charging.html

I know it's kind of wandered off Chris's topic a bit but often battery failure is attributed to poor batteries when infact the finger should be pointed to the charging.

Anyway, Chris - good luck with your twin batt install!

Poly · 15 January 2007, 20:15

Quote:

Originally Posted by Aidan

What do you think of the idea of a Power pack. I expect to get one at Aldi Ireland special offer this thursday for €40.
They are most useful and can be used to ballast bow. I would be probably better of buying a Bosch one. DOnt know what it is bit Bosch always seems to work better.

Aidan, I have one of these wired in (cut off the aligator clamps), to start my engine in place of a "normal" battery. It was cheaper than getting a battery, main isolator switch, putting a fuse and 12V socket in for charging phone/radio/gps etc. It lives inside the console to keep it dry. Light is useful as an interior light for the locker.

BUT I only did this because I have a hand start on the front of the engine (battery is mainly because I am too lazy to get up from console to start engine! and I wanted the option for a fixed VHF etc in the future). Its been fine for a year (lives in a garage when out the water) - but I wouldn't rely on it. There is a backup "cord" for the standard hand start too; and it is just a wee engine so easy to turnover.

Mine was a relatively cheap one (£30 ?) and holds charge well.

jwalker · 15 January 2007, 20:15

Quote:

Originally Posted by al40

Stage 3 - float / trickle. significantly lower voltage (13.4 to 13.8V) to keep battery fully charged.

So, if you are only ever applting 13.8v, you will not correctly charge your battery and it will loose capacity and die early.

al40, I think we're talking across each other a wee bit. In the system I proposed, the float voltage is all that is required because it's a backup battery and not in normal use. I presumed one would fit a charged battery in the first instance.

Quote:

(I trust the KISS was not aimed at me - partic the stupid part :-) )

Sorry, I wasn't meaning to be insulting. Perhaps I should have put KIS.

Aidan · 15 January 2007, 20:53

[QUOTE=Polwart;182053] Aidan, I have one of these wired in (cut off the aligator clamps), to start my engine in place of a "normal" battery. It was cheaper than getting a battery, main isolator switch, putting a fuse and 12V socket in for charging phone/radio/gps etc. It lives inside the console to keep it dry. Light is useful as an interior light for the locker.

I am a shopaholic anyway. I must have more of Aldi and Lidl stuff and as for Power drills, I highly recommend Bosch among the many units I must have. Alot of this stuff is junk but some of it is great.

I would possibly leave the croc clips is female socket so that I can bypass Trim switch.

It seems like a great little gadget and I cold also use it to Jump starts.
Will it charge from the Boat engine?

al40 · 15 January 2007, 20:55

Quote:

Originally Posted by jwalker

al40, I think we're talking across each other a wee bit. In the system I proposed, the float voltage is all that is required because it's a backup battery and not in normal use. I presumed one would fit a charged battery in the first instance.

Agreed, if the battery is fully charged then it's prob OK but if it does discharge I'd be inclined to give a good proper charging by shorting out that diode!

I never knew about all this charge graph stuff till I really started to look into it (was concerned I'd boil my battery in yacht with a standard fast charger). It's likely more of an issue in a yacht where you run the engine for a few hours a day but electronics, fridge etc run for 10-12 hours so you need to get as much charge into the batt as possible when engine is running. RIB's thankfully are a bit different. The smart chargers are big business at the moment - I wonder if they will ever take off in RIB's - maybe not.

Quote:

Sorry, I wasn't meaning to be insulting. Perhaps I should have put KIS.

no probs - no insult taken.