Quote:
Originally Posted by oldtamiyaphile
What would happen if you ran 15v to it, fooling it into thinking the battery was full? Or something along those lines.
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Yes, well, that was my original idea, way back before I got the DC/DC converter that outputs 14v. A simple solution, and it might just work, but I am where I am with the kit I've already got.
1. I could try to repair the alternator I apparently fried a few weeks ago when I tried to ground the field winding to effect an alternator OFF switch. (I wish I hadn't done that!) I'm really not confident of my ability to repair it though.
2. I could also get another used alternator and hope it doesn't self-excite. The last one didn't.
Or I could take the opportunity to work out a method of switching the alternator both ON and OFF. (With the 'old' alternator I could switch it ON OK, but I failed to find a way to switch it OFF while the engine was running. A proper ON/OFF switch would be cool because then I could wire the alternator in with the brake lights or an inertia switch for regenerative braking.)
A 15v feed ought to switch the alternator off, and switching the 15v feed current off ought set the alternator charging again. I think it would work, if I could get hold of the right kind of DC/DC converter to do the job, but 15v is slightly too high for the Odyssey starter battery. When the starter battery in the engine bay warms up to 40 or 50 degrees C, then 15v would overcharge it badly. Odyssey batteries really don't like being charged above 15v I believe. I think I'm too far down the 14v route to change to 15v now.
3. Another possibility is to put the alternator's +ve output through a high current relay (or solid state relay) with perhaps a 2 ohm bypass resistor so it never switches completely off but cuts down to a couple of amps output in the OFF position. That ought to work with any alternator.
4. Or I could search around and find an alternative alternator which will fit, and which is designed to be switched on and off.
5. Or I could just throw some heavy lead acid batteries at the problem, and have such a large bank of batteries that almost all journies can be completed without the alternator. Then I can disconnect all wires from the alternator and just make sure to carry the tools necessary to reconnect the main output wire if and when it ever becomes necessary. In fact this is probably the simplest option, as I have already made provision for fitting a second 105Ah Yuasa deep cycle battery in the spare wheel well. I wasn't sure I wanted to carry around all that extra weight (another 30kg) but from an electrical point of view it would make for a much better system as the batteries would be well within their comfort zone during normal everyday driving, so should last for years. And on longer journies I should have several hours of alternator-free driving time, even with headlights and/or wipers running. There's bound to be a slight mpg hit from the extra 30kg, but it's a 1500kg car and 30kg is only 2% of 1500kg. I very much doubt the mpg hit would be as much as 1%. Option 3 (above) would probably have a similar mpg hit as the alternator would be producing a couple of amps at all times, and the field winding would be energised at all times.
If anyone has any bright ideas, or can tell me how they managed to disable/re-enable their own alternator, please let me know!