How long will my battery last with accessories plugged ?

JX · Post by JX » Thu Jun 07, 2007 8:08 am

Hi,

I have just bought a bongo Turbo Diesel, and I have got a few questions. My Bongo is fitted with 2 batteries and this looks factory mounted. I have seen on other posts that this is not a leasure battery (unfortunately), but that both batteries are parallel mounted and both deliver juice to the cigarette lighter socket at the back (as well as to the rest of the electrical bits). I am correct ?
So I guess that if I spend the whole evening listening to the radio, with a WAECO 12V Fridge plugged and I watch a DVD on my laptop, both batteries ay be flat.
Question is (for now) : how long can I expect to run the frige and a 100W laptop (plugged to a 300W converter 12V/220V) ? Is it better to have a 100W Converter ?

Hope this makes sense... Excuse the english, I am french (in New Zealand).

Thanks !

moonshine · Post by **moonshine** » Thu Jun 07, 2007 9:19 am

Hi JX,
You are quite right about the batteries being in parallel and delivering power together.

Provided that your Waeco fridge is a compressor model, it will draw little power in one evening, and it will be the same for the radio, so they won't be a problem.

The laptop draws 100w whether it is run from a 100w inverter or a 300w one. The larger inverter will draw slightly more power to run itself than would a 100w one, but it will simply have more unused capacity. It will not draw 300w unless you plug more things into it. You are better to use the 300w inverter with your laptop, as a 100w one would be running on its limit.

I would have thought that if your batteries are both in good condition, and it is only for one night, you should be ok provided you go for a run in the morning to recharge the batteries.

For the longer term, it is quite easy to convert your setup to use one battery as a leisure battery.

Hope my explanation makes sense, and incidentally your English is very good!

haydn callow · Post by **haydn callow** » Thu Jun 07, 2007 10:00 am

I have the same set up as you and the same problems. I bought on ebay for about £4 each 2 battery terminal isolater clamp/switches. 5 min job to fit. When you get to camp, just unscrew one clamp 5 sec job and you can use as much as you want from one battery knowing that in the morning you can screw the clamp back up and have a full battery. If this dosn't make sense PM me or phone 01458 270230. I can email photos. Very simple and quick and cheap answer to the problem

bigdaddycain · Post by **bigdaddycain** » Thu Jun 07, 2007 10:39 am

Thats a good idea Haydn, a bit cheaper than a full leisure battery set -up too.

JX? Haydn's suggestion seems a very good idea, that way you are virtually guaranteed to be able to start your engine the following morning

Its probably worth having the condition of both batteries checked, as a precaution though... Your english is better than most english people's use of the language by the way

mikeonb4c · Post by **mikeonb4c** » Thu Jun 07, 2007 10:58 pm

You beat me to it haydn! I have one of those, cost a few quid off ebay, but cant think now why I have it since thanks to corblimey I now have a voltage sensing relay thingie.

johnzbenson · Post by **johnzbenson** » Fri Jun 08, 2007 1:50 am

The manual isolation of one battery seems to be a no frills simple way to go to ensure starting capabilities. Wiith respect to having two batteries wired in parallel then, in theory if they are two 105AH batteries the combined capacity will be 210 AH. As a good rule of thumb discharging down to 50% of this figure should leave you with good starting capbilities.
so how to work it out- difficult with a fridge which will switch on and off depending on the ambient temperature and how full the fridge is and of course how often you open the door, a 300w rated converter will NOT continually draw 300 watts . it is just what the converter is capable of delivering- the true current demand is decided by the load applied to the converter for example a 200 watt kettle etc.
I guess the best way would be to check the loading with an ammeter or if you have the wattage of a device then do a simple calculation. Watts is equall to volts (always 12v) multipled by the current. therfore if you have a 100watt lamp then this will have a current draw of (100W divided by 12Volts = 8.3 amps) Finally to figure out how long it will a take to discharge a 105AH battery the rating says it all. In good condition the battery will deliver 105 amperes for one hour or a 100 watt load (that equates to 8.3 amps) will discharge the battery in 12.65 hours, a 200 watt load will take half of this time.
I hope this helps a little and bonne chance avec le voyage de la Bongo!

JX · Post by JX » Fri Jun 08, 2007 7:53 am

Thanks everyone ! How come I did not think about Haydn's solution myself ??? I will definetely do that ! I am keen to have photos though just in case I misunderstood, but this looks like the kind of battery connection there was on the battery of my good old 205 back in France.

A la prochaine et merci encore !

swifty · Post by **swifty** » Fri Jun 08, 2007 8:23 am

Am using one of these auto relays, really desingned for caravan accessory feed off 12s socket on towbar but seems to work well for this application.

It effectively isolates leisure battery when engine not running, when alternator lifts main battery voltage to 13.8v relay clicks in and provides charging current for second battery. Bit close to the wire as it is only rated at 30A but so far so good

http://www.towsure.com/product/1828-Sel ... tion_Relay

swifty · Post by **swifty** » Fri Jun 08, 2007 8:25 am

PS

got mine on E Bay for £6

smartmonkey · Post by **smartmonkey** » Fri Jun 08, 2007 11:28 am

It might be worth putting a liesure battery in as the second and disconnecting the first battery for overnights. The liesure battery will take better to frequent discharges and will power your equipment longer.

haydn callow · Post by **haydn callow** » Fri Jun 08, 2007 6:13 pm

Another bonus of these battery isolator clamps is that you can unscrew the big contact bolt and take it away. Good anti theft measure. Only takes about 10 sec to remove both of mine and would mean a scrot would have to be very determined to get the Bongo started.

swifty · Post by **swifty** » Fri Jun 08, 2007 8:36 pm

Yeh But!

the relay does isolate the second battery except when the engine is running

pippin · Post by **pippin** » Fri Jun 08, 2007 10:25 pm

The use of an isolating switch is a very simple idea, but I think it has limitations.

Firstly, that it requires one to REMEMBER to do the changeover.
Forgetting to do so on parking up will have inevitable consequences.

Secondly, if one battery is totally flattened by your secondary loads and you then reconnect the other one, it is unlikely that there will be a 100% transfer of charge.
Remember, that to charge a (12V nominal) battery requires a voltage of some 13.8V.
A fully charged battery has a terminal voltage of approx 12.8V immediately after charging.
Connect a flat battery and the voltage of the two will equalise at well below that 12.8V ideal.

I have not proved this from experience.
However I do know a lot about lead acid cells.

pippin · Post by **pippin** » Fri Jun 08, 2007 10:27 pm

Smartmonkey, it would not be that easy to isolate the battery on the offside due to the way the two are interconnected and to the way the feeds are taken off to the rest of the vehicle systems.

swifty · Post by **swifty** » Fri Jun 08, 2007 11:16 pm

Yeh but, yeh but

the relay is automatic!

only connects to main battery when main battery reaches 13.8v This 13.8v is nominal charging voltage from alternator. The relay is adjustable to trip in anywhere between 10 and 14v. When the engine is switched off main battery will show only just over 12v at best, the relay turns off and second battery is isolated, has worked in my previous van for the last 8 years

How long will my battery last with accessories plugged ?

How long will my battery last with accessories plugged ?

Batteries and current discharge