DENBOY Posted March 14, 2008 Share Posted March 14, 2008 Hi all, just got my inverter (700 watts) and was wondering how many amps the alternater puts into the coach battery through the onboard system. I know alternaters can put 50+ amps out and wondered if running the engine whilst using the inverter the system would "keep up". Also I've heard that certain battery chargers don't like inverters any advice would be helpfull. Also what size fuse should I use on the 12 volt supply. Link to comment Share on other sites More sharing options...
Clive Posted March 15, 2008 Share Posted March 15, 2008 This is a meaty question. A 700 watt inverter operating at full output an assuming an efficiency of 90% will take in the order of 65 amps if the battery terminal voltage is 12 volts. You will need to mount the inverter close to the battery and use its supplied short fat wires and probably a 80 or 100 amp fuse. Your vehicle alternator is most likely capable of providing 90 or 100 amps. However the split charging relay and wiring will most likely have enough resistance to limit the current flowing into your leisure battery to much less than this, 30 amps if you are lucky and the split charging fuse does not pop!. If you wish to follow this route then you would be well advised to get the split charging wiring replaced with cable of say 25 sq mm (welding cable) and the relay by a contactor of suitable rating from Albright Engineers. The split charging fuse and holder also with one rated for 100 amps. Don,t forget to also replace the chassis connection to the leisure battery with welding cable as well. Hope that helps? C. Link to comment Share on other sites More sharing options...
Clive Posted March 15, 2008 Share Posted March 15, 2008 Pondering over a beef burger lunchtime and the throught came to mind, If you ALWAYS intend to run the inverter when the engine is running it would be a lot simpler just to connect the inverter to the starter battery. Then the alternator would keep up with the requirements of the inverter and you don,t need change any wiring or relays???? So now you have some choices! C. Link to comment Share on other sites More sharing options...
DENBOY Posted March 15, 2008 Author Share Posted March 15, 2008 Clive, I was really only hoping for a reasonable recovery time when i do run the engine. Using the inverter only when the engine is running was'nt the idea, may as well have a generator. But you got me thinking about the earth strap and when I checked it I found while the positive lead was fine the earth connection is two lengths of very thin cable nowhere near 70 amps and this looks like it was from new! The inverter will be in the glove box wired to the battery two feet away with a hefty 2 pole isolater and fuse. The plan being not to have any 12 volt to the unit untill I need it and use a standard extension lead ran from the unit to whatever. Thats the plan anyway! Link to comment Share on other sites More sharing options...
Clive Posted March 15, 2008 Share Posted March 15, 2008 At least it made you check things out. Take care and good luck. C. Link to comment Share on other sites More sharing options...
Brambles Posted March 16, 2008 Share Posted March 16, 2008 Denboy, Your battery probably will not charge as fast as your invertor can take it out, all depends on the spec of the battery. With modern low maintenance batteries and say 80 Ah, the charge rate might only be about 8 Amps, possibly higher when engine is run faster or battery is very low on charge you will get a lot more. This is not dependant on the alternator power but voltage and battery characteristics. I would be reluntant to power the invertor with engine running, as mentioned some alternators do not like invertors, reason being the peak spikes of current it takes. If the battery can cope with this and smooth them out the alermatoir should be fine, but if you baterry is aging and struggling with the spikes of current then the alternator will try to supply the peak current flow and will not do it any good at all and could lead to over voltage spikes hitting the vehicle electric system - not a good idea. Hope this helps. Jon. Link to comment Share on other sites More sharing options...
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