I bet you are all going to think this is a dumb question, but remember we aren't born knowing these things!
When we bought our new van last year it didn't come with a battery, so before we set off on the big one this year we had one installed. We went unpowered for a few days for the first time recently and it worked fine. We had the fridge switched to gas and ran lights, water pump etc on DC. We then did a long tow out, with the fridge and van power set to DC, and when we stopped for lunch, with the car still connected to the van, we found that the water pump didn't work. We tried the lights and they didn't work either. Although the fridge was still cold at that stage, by the time we got to our destination that evening it had started to defrost.
We thought that the DC power would draw from the car if it was connected, and only from the battery if the car was not connected, but this was obviously not happening, and the battery had been exhausted. The battery charges fine when we are plugged in to power at the caravan park.
What are we doing wrong? Or has the battery not been installed correctly??
dave06 said
07:58 PM Sep 29, 2009
mate you cant just chuck another battery in the van without an external recharging source and expect it to last
to acheive the type of ancillary power you want you will have to have a battery isolator installed on the motor vehicle (tow car) and then run a recharging wire back to the van via an anderson plug to the secondary battery
treat this setup exactly as you would by having a dual battery system on your car the only difference is you have a longer recharging wire back to the second battery
think about a solar panel setup as well, an 80 watt "briefcase" type will do you, a lot easier than running the second wire
Basil Faulty said
02:15 PM Oct 2, 2009
Due to the resistance in the wire from your car to the battery in the van you may find that towing all day does not charge the onboard battery. Lead acid batteries need around 14 volts to charge. It has to be done properly to do the job properly. You actually need a seperate circuit directly from the alternator to the van and prefferably no connection to the car battery at all which eliminates the need for diodes to stop the van battery from trying to provide power to start the car which means you don't have to overcome the voltage drop of the diode. As it is if it's wired up like most are you are taking 12 volts from the battery in the car and want it it to charge the battery in the van, the voltage drop over the diode will be maybe .7 - 1 volt which means your van battery is really only floating at around 11 volts. Now a lot of auto elec's treat this as they do putting an extra battery in a car and it just doesn't cut it, they assume that what they are creating is 2 batteries in parrallel which they are however the circuit resistance in this case leaves the second battery wanting...
Though the symptoms would suggest that there is no power getting to the fridge from the car to flatten the van battery. I would make sure that the only way the fridge could run of 12 volts was via the connection to the car and not have a situation where the car is charging the battery which is feeding the fridge, if you get my meaning.... sounds like double dutch? don't worry someone will fix this up for me.....
Rolly said
02:46 PM Oct 2, 2009
Collyn Rivers, a person of considerable technical knowledge and an ability to put complex issues into relatively simple words, has written several books for the RV user and one especially about this topic.
He also writes articles on many topics in various magazines and fora, gratis.
Well worth accessing.
oldtrack123 said
10:15 PM Nov 17, 2009
Basil Faulty wrote:
#1 You actually need a seperate circuit directly from the alternator to the van and prefferably #2 no connection to the car battery at all which eliminates the need for diodes to stop the van battery from trying to provide power to start the car which means you don't have to overcome the voltage drop of the diode."
Hi re #1 Yes definitely a separate circuit all the way from the car battery to the van battery, Use a Redarc or ignition controlled relay to isolate when engine is not running Cable both positive & negative should be minimum 6b&s If you have 3way fridge which you run on 12v while travelling, run separate cables back for it too & use a fridge switch[motion detecting switch] to shut it down when stopped Standard trailer plugs will not carry the currents [amps] involved need to fit heavy duty socket & plug [50amp min]
#2 do not know how you can isolate alternator from batteries without using a relay [ preferred or old fashioned but cheap diode method & yes they do give a voltage drop which affects 2nd battery charge
I bet you are all going to think this is a dumb question, but remember we aren't born knowing these things!
When we bought our new van last year it didn't come with a battery, so before we set off on the big one this year we had one installed. We went unpowered for a few days for the first time recently and it worked fine. We had the fridge switched to gas and ran lights, water pump etc on DC. We then did a long tow out, with the fridge and van power set to DC, and when we stopped for lunch, with the car still connected to the van, we found that the water pump didn't work. We tried the lights and they didn't work either. Although the fridge was still cold at that stage, by the time we got to our destination that evening it had started to defrost.
We thought that the DC power would draw from the car if it was connected, and only from the battery if the car was not connected, but this was obviously not happening, and the battery had been exhausted. The battery charges fine when we are plugged in to power at the caravan park.
What are we doing wrong? Or has the battery not been installed correctly??
It has to be done properly to do the job properly. You actually need a seperate circuit directly from the alternator to the van and prefferably no connection to the car battery at all which eliminates the need for diodes to stop the van battery from trying to provide power to start the car which means you don't have to overcome the voltage drop of the diode.
As it is if it's wired up like most are you are taking 12 volts from the battery in the car and want it it to charge the battery in the van, the voltage drop over the diode will be maybe .7 - 1 volt which means your van battery is really only floating at around 11 volts.
Now a lot of auto elec's treat this as they do putting an extra battery in a car and it just doesn't cut it, they assume that what they are creating is 2 batteries in parrallel which they are however the circuit resistance in this case leaves the second battery wanting...
Though the symptoms would suggest that there is no power getting to the fridge from the car to flatten the van battery. I would make sure that the only way the fridge could run of 12 volts was via the connection to the car and not have a situation where the car is charging the battery which is feeding the fridge, if you get my meaning....
sounds like double dutch? don't worry someone will fix this up for me.....
Collyn Rivers, a person of considerable technical knowledge and an ability to put complex issues into relatively simple words, has written several books for the RV user and one especially about this topic.
http://www.caravanandmotorhomebooks.com/
He also writes articles on many topics in various magazines and fora, gratis.
Well worth accessing.