Battery backup

[Observer]

Referring back to recent thread started by Happy1 -

I'm thinking about a booster or spare battery backup for our RIB. I want: (a) backup for engine starting in case existing battery fails (70hp outboard); (b) power supply to run electric inflator for water toy (concerned about draining the main battery).

Can somebody advise on whether better to go for booster or simply buy a spare battery (comment in last thread said booster needed to be used regularly or would deteriorate).

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[BarryH]

Personally, I'd put a second battery in with a batt switch. Its there all the time gets charged as you run the engine, less of a prob stowing it and cheaper. I used to have one of those power bank things. Died in less than 2 years.

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[DavidJ]

Agree with Barry, keep it very simple. A simple switch and not any clever power sharing electronics. Have it so you can isolate or switch in each or both batteries.
David

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[Happy1]

It's personal choice really. You have flexibility with the booster and can keep an eye on its charge by looking at the dial. A spare battery could go flat and you have to ensure it is kept charged. To me it just seemed a waste of money to leave something lying there you may never ever use, at least I can use my booster to run 12v ciggy socket things, recharge mobile phones, pump up the dinghy with the super dooper inflator e.t.c. It lasts for 50hrs use and does tell you how many charges you can do, 1,000 rings a bell. Mine has the blow up inflator on the side, which really is not much use to me, perhaps one day for a tyre but I have a small independent one for that. So perhaps get one without it, but the price of mine was dirt cheap with it and there was no other option.

So IMHO I think you get better value from the booster, think laterley (is that the spelling?) and work out the pro's and con's for your needs. The booster is nicely contained with a handle so if you use it you can take it home to charge it, more aggro with a normal battery.

Good luck anyway, at least you are being responsible and doing your risk assessment, very commendable and a good example to others /forums/images/icons/wink.gif

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[Guest]

Have to disagree

Simple switches will mean that either one battery is never being charged, or they are joined at the alternator so both will run down together. More importantly, if you run two batteries directly off one charging system, then the healthier of the two takes all the charges, so the sick one never charges up.

The only answer, IMHO, is a split charge diode pack and a second battery. Also, there's a clever way to wire up the switches that I can dig out, if interested...

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[qsiv]

Re: Have to disagree

Absolutely.

A booster pack would be useless on a RIB - either it'll be visible and get wet, or ina waterproof box and never be looked at. Do the job properly, once, and then it will look after itself. If you want to be picky about weight, then one of the RedFlash batteries, which are designed specifically as emergency starting batteries might be just the job.

<A target="_blank" HREF=http://www.herts-web.co.uk/notes/aesirpower/redflash.htm>http://www.herts-web.co.uk/notes/aesirpower/redflash.htm</A>

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[andyball]

Re: Have to disagree too

The oft-mentioned "healthy one takes all the charge" idea doesn't always seem borne out in reality from my experience.

since 1987 I've run two batteries from one alternator on a van,using one to start bikes/cars/run interior lights, via a split-charge relay system. In that time have naturally renewed both batteries twice....never any problems (other than the obvious) when one battery is totally flat/worn out.

On my boat I have two batteries via the usual off/1/2/both switch.........find it v.easy to switch to both for normal running, then to 1 if we stop for tea/overnight etc, then back to both or 2 when engine started.

Some prefer two simple on/off switches instead.

So I'd buy another battery for £50 & a switch if needed.

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[Observer]

Summary (and thanks for tips)

1. Second battery does the job OK with simple 1/2/both switch (question: do I have to check alternator capacity is enough to charge both?) but possible/disputed issue over whether both batteries will receive equal charge.

2. Could overcome "equal charging" and "alternator capacity" problem/drawback by having 1/2 only switch (alternator charges one or the other but not both) but have to remember to alternate (pun acknowledged) regularly?

3. Am I right in remembering one should NEVER isolate batteries when engine is running because will damage alternator? If so, is it OK to switch between the two or is that also only when engine stopped?

4. Booster give additional functionality and versatility but need regular use/recharging.

Have I got this right?

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[longjohnsilver]

Re: Summary (and thanks for tips)

1 Yes, there is a formula but can't remeber it, something like 3x alternator capacity should equal total battery amperage

2 No reason why that shouldn't work, providing you don't switch to both

3 Correct, I think it's the regulator which will get cooked

4 No idea, can't see the point, will undoubtedly let you down when you most need it unless it's used regularly, and I bet it won't be!!

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[Happy1]

Re: Summary (and thanks for tips)

I was quoted £238 for the fitting of a second battery, that was part of my reasons for going booster. If you do it yourself perhaps it is not such a great waste. TR7V8 explained on one of my previous posts, the booster one I think what I needed to know to fit it myself, but I had already bought the booster.

Cheers,

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[DavidJ]

Re: Summary (and thanks for tips)

Point 3
The alternator surge diode will start to glow red hot if it charges open circuit (ie no batteries)...then I guess it fails
David

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[BarryH]

Re: Summary (and thanks for tips)

Never had a prob with one batt going flat. The regime I use is "out" on batt 1 and "back" on batt 2. Both are always upto 85% charge (you'll never get 100%) and have never let me down.

I think its folly going out with an engine that relies on batt power to start it with only one batt. Especially an out board. OK, I know they give you that emergency start cord thing, but you try pull starting any sizeable outboard, I dare you to have a go with the emergency thing!!

The frying the diodes thing, yep it will happen in you run the engine with no load on the alt. A lot of the batt switches now have the Alt terminal which basically disconects the diode curcuits when you switch over from one to the other. Not hard to wire in once you identify the right wires to cut.

All in all I'd plumb for a proper battery set up on a boat that needs them. Much safer than messing about with crocodile clips in the engine compartment with the associated sparks coneecting them up.

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[andyball]

Re: Summary (and thanks for tips)

a battery should cost £50 ish....hunt down some good prices rather than breeze into nearest chandler & buy one. We've a cheap-cheap caravan "lesiure" battery as backup.....from experience you can run them totally flat many.many times & they'll still start a 2-3L engine w/o help from the main "starter" battery (once recharged of course).

I s'pose if you paid £80 for a battery,£25 for another switch, £20 for a box.cables etc...then £200+ is quite plausible for a dealer-fitted set-up.

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[pheran]

I agree separate battery and all associated gubbins is the more elegant solution technically. But from Wednesday this week, Macro are doing their booster/Portable Power Station for....................................£14.99 + vat. This is a genuine 17AH jobbie that other outlets are doing for £40 plus. Buy half a dozen and start a Centurion tank. Still shows a profit.

Oooops - should have said, no commercial connection with Macro!!

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[DavidP]

Hi

I see on some of the threads here people talking about battery switches ,,, 1/2/both, well this i have on mine , when ever i turn it on i allways turn it to 2 , because i have 2 batteries on the starboard engine, ,,, question what does 1 and both do and should i be running with it on 2.
The port engine has one battery with a on /off switch i know what that does ;-)

Cheers Dave.

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[Observer]

Ahhhhh. Well I think that position "1" is battery 1, position "2" is battery 2, and "both" is batteries 1 and 2 together. You seem to be thinking "1" is one battery, "2" two batteries etc. Not correct, I think.

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[Guest]

Well, at that price

it's worth carrying one.

Just got me into thinking about what we carry, in terms of spares and safety gear. Might make interesting reading for Happy:

Engine spares (2 sets) - drive belts, filters (oil/fuel), separators, impellers, 5 litres engine oil.

Fire extinguishers - 2 x 2kg powder auto in engine bay, 4 x 1kg manual powder (cockpit, galley, aft cabin, saloon, fire blanket in galley.

Electronics - Fixed VHF, handheld VHF, fixed DGPS/plotter/radar, handheld GPS, TV & video, Playstation, radio/CD player

Other - steering compass, radar reflector, toolkit, flares, spare anchor & warp, lifejackets for all, 2.7m tender with 8hp O/B, 2 x battery banks (165/115Ah), 2 x buckets, backup fridge, 300W inverter (don't ask what for, it was cheap), BIG first aid kit, paper charts, hand bearing compass

There are probably a few bits we ought to carry as well, but I can't remember what they are.

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