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Car Forum / MINI / November 2003Mains invertor on a standard alternator?
Is anybody able to tell me the output of a standard mini alternator? I've been told that it's likely to be 30 amps on my '87 city E. We're looking to run a 300w invertor (long story), so by the rules of physics, 300w / 12v = 25a What's not clear to me is whether the alternator would always be using that much power, or only a mains appliance rated at 300w was plugged into it? We're wanting to run a PC off of the invertor, to go along with a fancy MP3 system. Only a very basic PC, so I can't imagine it using much power? Can somebody more clever than myself please enlighten me? Thanks, Dan > Is anybody able to tell me the output of a standard mini alternator? > I've been told that it's likely to be 30 amps on my '87 city E. We're [quoted text clipped - 11 lines] > Thanks, > Dan I would expect the 87 car to be fitted with a 45 Amp alternator. The earlier ones were 34 Amp.  SignatureRgds Steve steve@dsnclassics.co.uk www.dsnclassics.co.uk > Is anybody able to tell me the output of a standard mini alternator? "standard"??? hehehehehe You think they ever actually built more than three minis in a row the same? > I've been told that it's likely to be 30 amps on my '87 city E. Comic cuts aside, I've seen Lucas alternators from about 22 to 35Amps in Minis, but it's not hard to fit a Bosch or other larger unit. > We're looking to run a 300w invertor (long story), so by the rules of physics, > 300w / 12v = 25a If you're pulling the full 300w from a running motor at 13.8V, you're looking at about 22A plus another 10% to 15% for the innefficiencis of the inverter, so, yeah, roughly 25A. > What's not clear to me is whether the alternator would always be using that much > power, The alternator doesn't use (electrical) power, it produces it! > or only a mains appliance rated at 300w was plugged into it? The inverter's DC consumption is negligable at no load and is typically about 10% more than it's AC output. > We're wanting to run a PC off of the invertor, to go along with a > fancy MP3 system. Only a very basic PC, so I can't imagine it using > much power? Measure it by plugging the PC into the inverter and running the inverter through an ammeter off a car battery. > Can somebody more clever than myself please enlighten me? If you want to run the car as well as the PC, you're going to need more alternator. If you want to run the system with the car stationary, you're going to be running the engine too fast with insufficient air flow and load. You're probably going to need more alternator. Simple non technical answer... Use leisure batteries to power the inverter. (Car batteries discharge too quickly, their designed for huge currents for short periods) Use a split charging system developed for the caravan market to recharge them. For the alternator to output near full power the car's engine will need to run at a higher speed than just idle, so from a noise factor it not ideal for audio equipment is it. > > Is anybody able to tell me the output of a standard mini alternator? > [quoted text clipped - 40 lines] > > You're probably going to need more alternator. > Simple non technical answer... > [quoted text clipped - 6 lines] > run at a higher speed than just idle, so from a noise factor it not ideal > for audio equipment is it. There is little space to have a second battery in a Mini though! However, the thought of running the main battery below the level to restart the car is not so good. A simple split charge system is to use a standard 30Amp relay. Run a wire from the ignition light wire (brown/yellow if I remember correctly) to the relay coil and earth the other side. Then connect the positive terminals of the starter battery and secondary battery via the relay. Use suitably rated wire and connectors for this! This system will charge both batteries while the engine is running, but disconnect the two batteries when stopped. So you can run the secondary battery as low as you like and you can still start the car. Got this is my Land Rover and it works just fine. The proper split charge systems monitor the balance of charge and split it intelligently. For example it will tend to charge the main battery first to ensure you can always start the car. But they cost a fortune! SignatureRgds Steve steve@dsnclassics.co.uk www.dsnclassics.co.uk Thanks for eveyone's response! I'm thinking that an alternator with a bit more kick might be a good idea. Can anyone recommend a good place to get hold of one? Thanks, Dan > > Is anybody able to tell me the output of a standard mini alternator? > [quoted text clipped - 40 lines] > > You're probably going to need more alternator. The GXE2297 is a 45A alternator serch google for supplyers > Thanks for eveyone's response! > I'm thinking that an alternator with a bit more kick might be a good idea. [quoted text clipped - 46 lines] > > > > You're probably going to need more alternator. > Thanks for eveyone's response! > I'm thinking that an alternator with a bit more kick might be a good idea. > Can anyone recommend a good place to get hold of one? > Thanks, > Dan Are you absolutely stuck with the mains guzzling 300W PC ? A bloke at work used a mini itx pc to run an in-car mp3 player. The whole shebang including dinky lcd screen drew a tiddly 2A at 12V. Take a look at http://www.mini-itx.com to start with. Dave >> Thanks for eveyone's response! >> I'm thinking that an alternator with a bit more kick might be a good idea. [quoted text clipped - 9 lines] > >Dave I use a 933MHz Mini-itx PC. You can get cases with a 12V input PSU and only consume 2 to 3A at 12V. Couple that with a 12V LCD monitor and you're in business. SignatureChris Morriss
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