Battery help requested

dkm

dkm

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No genny fitted so thinking of getting an inverter so SWMBO can use hairdryer and watch corrie (separately). Can anyone tell me how I figure out the battery capacity (Ah), apparently need to help decide most appropriate choice of inverter?
Can anyone recommend the correct inverter to get?
Boat is a targa 34 with original fitted batteries

/forums/images/graemlins/confused.gif
 
A 1KW hairdryer will pull a huge amount of amps from the batteries at 12V (roughly 80 amps).

I simple terms, the more batteries you have (as in the more AH you have), the longer they will last when the required load is applied.

You will also need a substantial inverter to support that load continuously.
 
Battery Ah may well be marked on batteries BUT remember that a 600 watt microwave will consume 50 amps so will flatten your battery of 110 Amp hour in about 1 hour (I have been told that you should not allow the battery to reduce more than 50%).

Realistically you can only use the inverter for extended periods if the engine is running.

Tom
 
A 2KW hair-dryer?? 3KW and the motor on top of that if it's got Professional, Vidal Sassoon, or some such written on the side and an absolutely farcical price tag to go with it. /forums/images/graemlins/confused.gif

Make sure you get a pure sine wave inverter for the telly.

Find the the KW rating for Hair-dryer and get an inverter that produces that much. Try and get SWMBO to switch the blower on and let the fan run up to speed before she switches on the heating elements on the hair-dryer.

All the decent inverters have a surge rating that let's you get away with using an extra few hundred watts for a short period of time so you have a safety margin.

W=V x A so a 2400 Watt hair-dryer running at 12V will draw 2400 divided by 12 or 200 Amps (assuming the inverter's 100% efficient). In practice it'll be between 80 and 90% probably so say 230 Amps. A battery can go to say 50% of it's rated capacity so she'll flatten a 115 AH battery in 15 mins with a 2.5 KW hair-dryer.

Also you have all the other things using your batteries and draining them. so you need to take those into account. Lights, etc. all add up and 12V fridges are a killer. Find out the wattage of these items and divide by 12. That gets you the current in Amps. Work out how hours each item uses those amp for and you then have the number of amp-hours you are drawing from your batteries.

I'd guess at something like 3 x 115AH batteries in a Targa 34 so theoretically you get 45 mins or so but you really don't want to take your batteries to 50% charged on a regular basis and that's assuming nothing else being used.

Raggie's are a good source of information for this stuff as they have to watch power carefully given the lack of engine charging available.

I'd say you'll be marginal but may get away with it if

a) The hairdryer is only 2KW
b) SWMBO can dry her hair in 15 mins
c) You don't have much other stuff using the batteries
d) You recharge the batteries every 24 hours
e) Both engines start off dedicated batteries
f) The house batteries are in good condition

Failing that buy her a towel.... /forums/images/graemlins/blush.gif
 
The other option of course, is to get a portable genny!

This will be the best of both worlds, so you can always use it to charge the batteries, or use it to drive your domestic tools when working on the boat.

If you do get a genny, get one of the suitcase "quiet" genny's so you don't annoy other boaters when running!

You'll probably find it cheaper than an inverter system, when you take into account installation costs etc.
 
Tried a 12v hairdryer, about as much use as a chocolate teapot for my SWMBO
So..............a new towel it is then
 
We have a little fag lighter inverter, just for charging phones and stuff, ok some time runs the telly. Other than that the little Honda genny comes out, can usually park it about 20 yards away, down the pontoon.
 
My 2006 T34 has three batteries - Fairline only connect two to the mains charger for port engine and domestic services (135AH each as I recall). There is a third battery (185AH)serves only the starboard engine, but this is only charged when that engine is running.

At the helm there is an emergency changeover switch to start the SB engine from the Port batteries if the 185AH battery flattens.

Each battery has a certain life expectancy based on a number of cycles (or number of times used). Many factors affect the cycle life (battery technology & construction, charging method and ambient temperature) but it’s the depth of discharge that a battery experiences that is of key importance.

In short, the deeper the discharge, the shorter the life span of the battery.

So be very careful when using an inverter to support heavy loads, I agree with others, its not good practice to frequently discharge a battery less than 50% and frequent discharging to this level will certainly reduce battery life significantly.

On the T34 DC panel you should have an ammeter showing the current drawn by the domestic circuits, as others have said, for a purely resistive load (say heaters) this equates to Power (watts) = amps x volts or P=I x V you may also be interested that Power is also equal to voltage squared divided by resistance in ohms and also current squared multiplied by the resistance. Mmmm perhaps a small genny, thats what I use!
 
Well, I have such a set-up, as it happens.

Madam's hairdryer is 1500W, so I fitted a Waeco 2000W modified sine wave inverter. It is auto changeover, so the incoming shorepower is routed to the inverter and then to the distribution panel and the inverter switches off if shorepower is present.

To feed it, I have installed extra capacity and the starboard bank (domestic and stbd cranking) consists of 2 x 110 Ah and 4 x 85 Ah leisure batteries. If this lot is low, it will seriously overload the starboard alternator, so it is charged from both alternators via a Driftgate charge splitter and a smart alternator controller.

The LCD TVs, DVD and satellite box all work fine with a modified sine wave - an older CRT TV on a friend's boat has problems with the same inverter as does my daughter's GHD hair straighteners, for some reason...
 
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