I’m the guy who had the battery charger question for you. Thanks for running the course last weekend, really enjoyed it. Would have liked a bit more practical but realise limitations on time. Certainly picked up some useful info.
I have a query with regard to a problem we have with the boat electrics which I was hoping you might be able to suggest a way forward.When we bought the boat about 7/8 years ago she was already about 4 years old and fitted with 4 x 6 volt batteries to give us a 24 volt system. I think the batteries were original and within the first year we started having problems with the electrics, but generally more during the winter (fairly obvious really with lights being on more often). These 4 batteries were replaced with 2 x 12 volt 110 amp hr. ones connected in series.
The way we use the boat is that my in-laws go away on the boat during the summer months, April to end September usually. When they finish cruising for the day they will probably watch TV and have a shower in the morning and they did not suffer the problems we had. We have the boat out at other times of the year and usually over the Christmas period. We cruise for the day and will have a shower in the evening. We found that when we came to switch the TV on (a 10″ CRT colour portable) it would quite often not switch on unless I started the engine. So we then switched the TV on before we had a shower but the found that the TV would switch off part way through the evening especially if the water pump was run.
In trying to resolve the problem I found a duff inverter which was drawing current even when nothing was running off it. This has now been taken out. We have also replaced the CRT TV with an LCD one. The TV runs from a 24 volt to 12 volt converter and I have replaced the wiring between the converter and the TV with thicker material (as suggested by the boatyard). Last summer we had an Adverc fitted. Despite this we still have problems when we went cruising last September and more so over the Christmas period. We can cruise for 5/6 or 7 hours and if we have a shower in the evening we have problems with the TV. We still put it in before we have a shower and part way through the evening if the water pump is run or a light is switched on the picture goes off on the TV although the sound stays on. If we change the channel over the picture comes back on. We have also noticed that if we have had the lights on for most of the night, had the TV on and also had a shower, the water pump sounds very strained in the morning.
Here is a list of the electrical items we have on board:
12v radio/cassette 16w/channel. (which we rarely use)
TV 12v LCD 3.2amps
saloon lights (4) 24v 20 watts
table light 24v 20 watts
water pumps (2) one is rated at 1.8 amps the other 3.5 amps is used as a spare and is not connected.
shower pump out 24v 6.5 amps
lights over dinette, bedroom and engine room (3) 24v 21watts.
small lights over bed (2) 24v 21/6 watts.
Fluorescent lights in galley and bathroom (2 with 2 tubes in each) F13w/w
I’ve not included the tunnel lamp or the horn. We run the fridge off gas.Do you agree with the following calculation based on a typical ‘winter days use’:
hours used total amps TV 3.2 amps (not
sure about the implications of the converter)5 16.0 shower pump out 6.5 amps 0.5 3.25 water pump 2 amps 2 4 lights 3 amps assuming 3
lights at 1 amp each6 18 (not sure
about fluorescents)total 41.25ahr Does this seem reasonable and do you think that our battery bank of 2 12v x 110amp hr batteries connected in series should cope with this ?
Were you aware that all inverters draw a small current if left on with no load. In my view they need their own on/off switch – depending upon model allow about 1 amp = 24 AH per day.
Now lets look at the battery question. I assume your calculations are correct.
You now have an Adverc, so at we can assume them being 98% charged at the beginning of the evening as long as you have cruised enough during the day. We know that at 50% discharged the voltage and the life of the batteries drop. We do not know how sulphated the batteries are or how well they hold their charge, especially as the indications are that they have been too deeply discharged in the past.
98% – 50% = 48%.
48% of 110 AH = 52 Ah
So with good batteries, fully charged you have just 10AH spare. With the inverter in circuit you probably had a deficit of 14 AH, so you were discharging your batteries too deeply, shortening their life.
I think the 24 to 12 volt converter may be more inefficient than an inverter – how hot does it get in use. If it warms up its drawing current itself and probably dumps it to earth – not very efficient!
It looks to me as if your batteries are at or very close to the end of their life (I make them about 6/7 years old by your figures and suspect their life was up a couple of years ago, so you have done well). Get them tested at a battery specialist (yellow pages). I also think that you are cutting the capacity very close. If it was a 12v volt boat I would advise putting another battery in the bank, but two more is a bit expensive.
Questions & Answers courtesy of Tony Brooks of TB-Training
