12v nightmare,

[bramley]

Hi,

we bought a fridge freezer from midland chalnders 5 months ago, and have had hell since,

Our boat is 20 years old the wireing isnt the best but it looks solid and strong,

 

the fridge freezer we have is a fairly big one, 4ft tall it aparently runs at about 1.5amps a hour, its also aparently 53 watts, it runs for half hour of a hour,

 

I have fitted 5 new 110 amp batterys, and i have fitted a digital regulator, (sterling} we have a 90amp altenator.

 

The problem we have is we are having to run out engine a lot to keep the batterys charged, what midland chanders said is the the fridge will run for 1 week ish, without needing a recharge, i having to run every day for 3/4 hours, and its a compleate nightmare,

 

Both me and the girlfriend work and we get back at 6 ish to run the engine to 9 isnt what i want to be doing, at all

 

I was wondering what i could look for to solve the problems what could i test, i might thing we have a power drain, when i have finished charging the batterys the voltage is 13.4, then it drops to 12.8 in 10 minites, then it just drops in 36 hours it went from 12.8 to 11.5 with just the fridge running, I really cant see it to be anything else,

We do watch tv at night, its a small 50 watt tv, i do however have a big inverter, 1000watt, could that be using power??????/

 

Please can anybody give me any idears/experiance

Thanks

Ross

[John Orentas]

Ross.

 

You are asking too much of your electrical system.

 

Surprisingly the number and size of your batteries doesn't really come into the equation. Having a lot of battery capacity only allows you to go for a longer periods between recharges.

 

Having an alternator which is rated at 90 amps certainly does not mean you will get that kind of output even with a charge controller.

 

Your 53 watt fridge will draw 4.5 amps of 12 volt power though as you say it may be off for 50% of the time, even so it will, with losses be drawing 3 amps or more for 24 hrs a day.

 

Your TV with it's inverter will be drawing at least 5 amps for as long as it is switched on. Plus your lighting. Plus water pump and other things.

 

I won't go into the arithmatic, there is always lot's of debate over this with people having some kind of blind faith in charge conrollers but everyone will accept that losses are massive.

 

I would advise you to measure your charge output and your power consumption. Borrow or buy an ammeter don't make assumptions about inputs and outputs, then do some sums for yourself.

 

John Squeers

[nbtafelberg]

Hi Ross :-)

 

I would echo John's Post.

 

There are things you can do to help your cause.

 

1. Check your light bulbs, you can purchase LED light bulbs that use very little voltage - I'm buying some tomorrow hopefully so I'll let you know how I get on with them. Anything you can do to reduce input will help.

2. We run a Digibox, 12 v Fridge and a TV and lights (including some rather pretty Christmas lights) off of our 3 x 110ah leisure batteries. I have, like you a 1000w inverter. I also have a Solar Panel with a Charge Controller, I'm going to purchase another solar panel shortly to up the input, these panels even work on a grey day, they just need light, but they do work better in the SUN. My 12v fridge works great, even has a little freezer. Also we have an excellent bolin pump for keeping us warm (along with the stove).

3. It does help if you can get a shore line ofcourse :-)

 

Only thing I will say Ross is that we've all been there, I'm not sure if your'e a "new" boater but after a time you get used to your systems and learn how to best manage them. 2 days after we purchased Tafelberg all our batteries failed and our gas ran out, so I know how frustrating it can be.

 

Perhaps you could have a separate battery for the fridge, i.e. split off one of the others and use a single battery for the fridge, you can then work out if it is something else that is pulling the batteries down.

 

process of elimination called for here.

Edited December 14, 2004 by clevett

[Khayamanzi]

In addition to the above posts, bear in mind that the more load you put on batteries the more the voltage drops but will re-gain when the load is taken off. In other words, if you are only looking at voltage read outs to see what charge is left in the batteries, it may give a deceiving reading. I run a microwave and at the point of running it, my battery voltage readout can drop to almost 10 volts but the minute the microwave is switched off, the voltage rises again to nearly 12. It would be worth sometime letting the batteries drain on 'normal usage' in order to really see what you can do and put your mind at rest. You may find that you don't actually need to be running the engines as much. I have exactly the same battery banks and ratings as you and when out cruising can run heavy electrical usage drawing an almost constant 20 amps all evening, including the microwave for dinner, shut everything down except the essentials over night and the battery meter still says I have about 11.5 volts in the morning with 70% remaining and an estimated 30 hours still to go, granted that even with an Adverk battery management system it still takes about 4-5 hours cruising the next day to charge to 100% but then my boat is designed for living off a land-line or cruising constantly when out however, if I was living off the land-line and so reduced all my power consumption down to the bare minimum it gives an idea what should be capable.

 

Most people in my marina who are running off batteries and don't have the land-line 'top-up' the batteries for about an hour each day and then give them a full charge at the weekend.

[dor]

Do you leave your inverter "on" when you are not using it? Some inverters have a significant quiescent current which is drawn whether anything is using the power or not. The efficiency of inverters varies a lot also, chances are your inverter draws more current to run itself than it is supplying for the TV.

 

You need to do a full energy audit to see how much power you actually use. The fridge will probably use more than you think. You can check this by connecting up a clock - some fridges have a switched output which becomes live when compressor is running - otherwise use a croc clip to connect to the compressor feed. If you can't find a 12v clock, use a little relay. You need to check how many hours the fridge is on over a 24 hour period, and in differnet conditions: warm cold, weekday, weekend.

 

Check the current draw as well, 54 watts sounds quite low for a large fridge, but it may be right.

 

When you add it all up, you find that running for 3 - 4 hours a day is about right.

[Guest]

Our Sterling inverter is claimed to draw one amp when idle. Some neighbours of ours have just bought a Honda genset which runs on propane. It is incredibly quiet. When we finally live aboard, this will be our first purchase. (I read of a Honda generator recently which had done a claimed 13400 hours).

Edited December 14, 2004 by stan hesketh

[Yamanx]

I agree, the measurment of voltage is not a good way of determining power usage.

 

However, if in 36 hours, without charging, you still have enough to run your fridge, lights and inverter. I'd say thats pretty good.

 

An inverter is only 90% efficient and to get 50w out you need to put 55w in regardless of volts.

 

You need to do some sums.

 

This chap from Reading College has been really helpful to me and really knows his onions. He's a nice guy and will give you the help you need.

 

brooksa@reading-college.ac.uk

[John Orentas]

Andy.

 

If your microwave is pulling the voltage down to 10 volts something needs attention. Measure the voltage at the batteries and the voltage as close to the microwave as you can. It may be simply that the wiring is insufficient.

 

As I have said before measuring the voltage of a battery does not give an indication of it's state of charge, but I would say that 11.5 volts off load is effectively a flat battery.

 

John Squeers

Edited December 14, 2004 by John Orentas

[Khayamanzi]

Thanks for the last comment but the only thing I know works in top class condition is the electrics on the boat now! Since hitting the press in the summer with the whole electrics system bursting into flames on a brand new boat, I now have a completely re-wired boat which has also been independently checked by several organisations, (I insisted it!!) The size of cabling was an issue along with my friendly boat buildres not wiring all appliances via the shunt but these are not any more. The voltages stated in my previous post were not necessarily with a 100% battery bank charge, the microwave is quite a high power one, (drawing nearly 200A at full power!) the inverter takes 5 amps to run itself and I would normally also be using the digital flat screen TV and possibly desktop PC to download the latest photgraphy images!! Hopefully this puts things into context!

Edited December 14, 2004 by Khayamanzi

[John Orentas]

Andy.

 

Much as I admire your faith and confidence in your boat builder.

 

Running what is essentially a 12 volt electronic device at 10 volts is bordering on the realms where trouble becomes a bit more than possible, I will put it no stronger than that.

 

John Squeers

[Richard Bustens]

the microwave is quite a high power one, (drawing nearly 200A at full power!)

 

 

Are you sure?

[Yamanx]

the microwave is quite a high power one, (drawing nearly 200A at full power!)

<{POST_SNAPBACK}>

 

2.4kw microwave (At 12v) 48kw at 240v!

 

I bet you can cook a roast chicken in 2 seconds

Edited December 14, 2004 by Yamanx

[Khayamanzi]

OK for those like minded sad people interested in the finer details of my microwave oven!

 

Tested it tonight and it actually pulls 170 amps running at full power. Now, when I say 'it' pulls 170amps, I mean that the readout reads 170amps off the inverter, this also includes about 20amps of running fridge, Christmas lights, TV, digital box, freezer, PC and wireless broadband access point not to mention the inverter running itself etc etc. I guess the microwave actually pulls about 150amps. When my batteries read 11.5 volts, this is in the morning and so I wouldn't expect the system to be 'full' (whatever that may be!) The 30 odd hours it says is still remaining is at the early morning discharge of around 1-2 amps. My inverter has a default pre-set of knowing that there is insufficient input charge to run itself at around 10.5 amps and so still considers there is enough charge down to that level. In fact on occasions I have managed to run the washing machine down at the level in the batteries off the inverter and only half way through the wash did the inverter say 'error code E2' which means insufficient input current. At that point it decided to shut down!

 

Billions of people have told me off for over-exaggerating!

 

Does that clarify the 'turkey cooking itself in 2 seconds' situation??

Edited December 14, 2004 by Khayamanzi

[bramley]

Hi., thanks for the mass of replys

 

Personaly i thought 53 watts for a fridge of this size was to small.

 

i know it varys but i think at 11.5v my batterys are flat?????

 

basicly i get the idear i should of bought a gas fridge or a smaller 12v fridge (i planed to do this but was upgraded by salesman)

 

i battle im in is to return the fridge under the pretenses it was sold to me without the true figers

 

i just dont like running the engine for so long, a it puts more hours on the engine, b its just not nice for neibours even, theres only one boat near us, they said they dont mind, but its still not what i want to do, and C, i like my relaxing time after work too

 

Thanks again

Ross

[DHutch]

2.4kw microwave   (At 12v) 48kw at 240v!

 

I bet you can cook a roast chicken in 2 seconds

 

I dont see why it can be 200A, like you so, at 12v thats 2.4kw, which is a possable

 

i just been testing our old microwave (at home) and i get measurements of

at 240v, 6.34A, 1.45kw (1500volt amps)

 

which if it where running of 12 (using a zeroloss inverter) 1.45kw whould be 104A (using P=IV) - and if it where a more powerfull microwave, runing though a 85% effecent inverter it could easyly be drawing 200A

 

 

also, on the topic of LEDs, i did some research a few weeks ago which showed that accutally flurecent bulbs are still far more effeicnt than LEDs which are infact barely better then a stardard halogen bulb!

- so for effecnt lighting, go for Flurescents, and for spot light, you might as well stick with the halogens from argos!!

 

[edit] the above was posted before any other replys had been made to tonight, becuase i took a while testing the microwave, dueing which time other people posted[/edit]

 

daniel

Edited December 14, 2004 by dhutch

[Khayamanzi]

12 volt website that may be useful!

 

Just for interest - this site may be useful and/or interesting. An American site that deals with 12 volts in the context of RV's (recreational vehicles) but principles apply. It is interesting to note that most batteries are recognised to have a cut off point of 1.75 volts per cell which equates to 10.5V on a 12V battery and the battery standard is that they are tested to ensure that they can sustain a constant load of 25Amps at a stable 80'F, so long as they don't cut out until that point, they are still considered to 'hold charge' Now I sound like a real egg-head! (This isn't the everyday sort of knowledge I carry around you must understand, I discovered it on the above site and clarified it with my friend who happens to be the MD of Plessey South Africa and has a PHD in electronics engineering!)

 

Click for a useful battery state charge table.

Edited December 14, 2004 by Khayamanzi

[Khayamanzi]

Sounds as if we have a resident expert in the form of Daniel here - you've blown me so to speak!!

[ChrisPy]

Sounds as if we have a resident expert in the form of Daniel here - you've blown me so to speak!!

<{POST_SNAPBACK}>

you guys run some mighty big microwaves !!

 

What rating is this 150A/200A microwave?

 

I wouldn't want to run anything bigger than 750W, and I assume that will pull no more than 80A including inverter and cable losses.

[Khayamanzi]

Mine's rated at 750Watt or so it says on the front!

[ChrisPy]

Mine's rated at 750Watt or so it says on the front!

<{POST_SNAPBACK}>

does it say on the maker's plate what is the power consumption and current rating?

 

if its pulling about 140A and putting the equivalent of about 11Vx70A into your food, there's an awful lot of energy being dissipated somewhere along the line ...................

Edited December 15, 2004 by chris polley

[Richard Bustens]

Hi

Well there is something wrong with my maths again lol

As i make it that a 750w usage @230v through a inverter with a 10% loss would be 71.74A

But as i always get the triangle the wrong way round. i am probably up the canal without a cooker.lol

[John Orentas]

Richard.

 

750 watts @ 230 v = 3.3 amps

 

+ 10% = 3.6 amps

 

John Squeers

[Richard Bustens]

hi John

So how many amps from a 12v battery then to run it

Is that not the same as i hrs use ie 71.74 ah to run

Is that not what the drawing from battery should be?

[DHutch]

I have a "plug in power and energy moniter"

 

It plugs in between the applience and the 240v socket (like the plug in timers you get) and the it tells you the voltage, frequency, amps, watts, voltamps, powerfactor, time and units used.

- its quite usefull for working out how much juice your diffrent things are using, and how long for.

 

daniel

Edited December 15, 2004 by dhutch

[DHutch]

hi John

So how many amps from a 12v battery then to run it

Is that not the same as i hrs use ie 71.74 ah to run

Is that not what the drawing from battery should be?

 

3.6 amps @ 240v is 72amps @ 12v