Battery Switch & Amps

[Forbsie]

I bought a battery switch today that I later realised was rated to 170 amps.

Am I alright using it with 2 or 3 x 130ah batteries and does this rating relate to the draw from attached appliances?

Thanks as ever,

Gordon

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[snowleopard]

yes, the rating of the switch is the current that will flow through it, nothing to do with the battery capacity. you'll be hard pushed to draw more than 170A!

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[stuartw]

And starting current?

Most battery switches are used to enable starting the engine from either battery or both.

Depending on the engine, but typically, the cranking current can be between 300 and 600 amps. Your 170A is a bit thin, unless you have a very small engine. For general services, then yes it will be fine, but not for starting.

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[john_morris_uk]

Re: And starting current?

Not sure where you get 300 to 600 amps from. My beta engine starter draws 66 amps. Also the switch rating varies according to whether its intermittent or continuous etc etc. To complicate things even more, the ratings of switches vary according to which standards are applied and to whether the switch is supposed to be carrying the current or switching it. If you look at the worst case of switching high current DC into an inductive load the problems are enormous, but the rating of marine switches often refer to the current they will safely pass - not switch.

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[Jean]

Re: And starting current?

For "battery switch" in this posting, I read "battery isolator", ie, not intended for switching the load (inductive or resistive)? Also, with battery isolators general, I favour one per battery, or battery bank and fitted at/near terminals. Because starter current is normally short duration, the 170 amp "isolator" will probably be OK (worth rechecking "switch" specification). I mentioned in another posting that I recently measured the peak starting current of a 36 HP diesel as 260 amps (with a decent meter), but, once engine has started turning (or warm), current should be a lot less. John, 66 amps sounds low for a 12 volt system. Was it peak or steady state and was engine cold?

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[Blue_Blazes]

Re: Electrics

At last, some people with electrical knowledge. Sorry to bust in on this thread with a repost, but when I posted this about 3 days ago I didn't get one reply on subject.


I never had a twin engined boat before. I'm now about to buy one that requires lots of work. Trouble is I don't know much about electrics in general, and twin engine electrics in particular. So can anyone tell me:

1) Do both engines usually have the same type/output alternator?

2)What is the normal setup as regards starting/house battery banks and their charging/switching arrangements?

3) If the engines are 24volt, is the "house" system/lights/instruments etc usually 24volt too? (I've only had 12volt up to now so pardon my ignorance).

Answers to the above and recommendations on reading matter would be most welcome.

Cheers,

Bill.



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[BarryH]

The switch will probably be fine for the installation that you will use. The 170A will be quoted as a continuous rating. The switch will prob have a peak or short period rating closer to 300 amps. You'll only really have to worry if you wanted to switch over batteries while under load, which you wont.

I've got a similar installation as yours will be. Never had a prob with it and nothing ever get warm while under load, even prolonged cranking of the engine.

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[tr7v8]

Re: Electrics

Bill,

to answer your questions:-

1. Yes
2. Normally (presumes diesel) you'd have 3 batteries, 1 per engine start and one for domestics. The one for domestics could be a bank of multiples all connected together. After that it varies typically each engine charges it's own start battery direct and then the domestic bank through a split charge diode, relay or similar.
Mines petrol and only has one start battery.
3. A very few run 24V start and 12V service but most run full 24V everything, most trucks are 24V so if engine derived from here then it will stay 24V.
Some use a voltage dropper to charge or supply a small 12V battery for odd bits like radios

<hr width=100% size=1>Jim

Draco 2500

 

[Blue_Blazes]

Re: Electrics

Many thanks Jim, that's made things a lot clearer for me.

Don't want to be a nuisance but I believe if you don't know then ask. So one more question if I may. The boat is a 33ft aft cabin Fairey Swordsman with Perkins T6354.4m engines. Both the engines are devoid of Alternators at present. What size/output of alternator would you suggest to meet the demands of this type boat/engine combination?

Cheers,

Bill.



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[snowleopard]

Re: Electrics

i would suggest aroound 50A alternators. with a powerboat you won't have problems with charging unless you spend a long time at anchor. there's no call for high-power alternators which cost a bundle. raggies need them to get max charge in min engine hours.

i recommend you fit a smart regulator to control both alternators and a splitting diode to divide each engine's output between the domestic bank and its own start battery. adverc do a twin-engine regulator and give very clear instructions on how to hook it up.

you will probably want to have the regulator wired to detect the voltage at the domestic battery bank as that is the one needing most charging. if the domestic batteries are not in the engine room there is a slight risk of overcharging the start batteries because they are hotter and have a shorter run of cable. the regulator manufacturers can advise.

if you can run everything off 24v, great. most people find that there are some gadgets obtainable only in 12v form, requiring a voltage drop device or separate 12v circuit, a real pain.

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[Forbsie]

Thanks, Guys.

Barry, was it you that suggested that I install some sort of battery management if I had 2 x domestic and one x starter? If so, any suggestions on most sensible one for cheap river cruiser. Also cheapest place to get switch panel and should I go for breakers at 10 times the price?

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[PaulJ]

Re: Electrics

Bill,
Have a look at the Adverc website (www.adverc.com) where there is a great deal of info on this kind of thing. If you click on "Technical" there are several articles on different aspects of installation, including a section on twin alternator installations

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[BarryH]

The battery switch should be fine. All you've got to do is get into the habit of switching the thing. I've had this set up on my boat for ages now. Never had any probs with it. You don't really need a smart charger like stirling or adverc. They're more for raggies who don't run they're engines for long.

Keep the cable runs short and once installed check the losses with a meter. Your engine takes no leccy once its running unlike my petrol. So you should be fine.

Swithch panels! Never like the breakers too much. Its too easy to reset the things without finding the fault if it pops. Call me old skool but I like fuses. Made a few switch panels in the past. You can get them engraved at most key places. Looks good and is a fraction of the others that are a bit of a compromise as far as labelling goes. Then just pop down to Maccess and pick up the switches at a fiver for 10. They also do the fuse boxes that are advertised in the boat mags at a fraction of the cost. If you want interior lights Orpington caravan and lesuire do a good range at reasonable cost.

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[Blue_Blazes]

Re: Electrics

Just had a look on www.adverc.com. Very interesting site. Obviously they want to sell you their system, but there's lot's of useful info too. Thanks Paul.

Bill.

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