rs 730 draining battery

Battery turned out to be bad guess ill replace it and see what happens

Well done. Howard pegged it so confidently (again!) but so did the later replies. [ How dare they - I though batteries were my forte, not theirs! (Of course a battery could always be the problem. The expertise is knowing that is isn't the alarm - and that's not my expertise!!) ] I merely wanted to add that hopefully whoever fitted your battery did an alternator voltage check after fitting. It amazes me how often that is NOT done. Hence if your battery failed due to over- or under-charging, the new one will do the same... My battery supplier always checks. His batteries typically last 8 - 10 years; even 6 years from battery abusers like me. Ironically they are cheaper than our KMarts, Autobarns and Super(NOT)cheaps.

Err Uncle Peter I DID mention alternator.

I know you did - I was merely emphasising the alternator effect - ie, that it might be the result of a bad battery, and many battery fitters do not check alternator voltage. As to determining a bad battery IF the alternator is faulty, well... IMO (read: d'oh!) you need to fix the alternator when or before fitting a new battery, but maybe the battery is ok & comes good after a good charge - whether a >20A charge or after an equalisation cycle. Then again a long discharged battery may seem ok but lack capacity (the old survive summer but fail winter routine). I just hate it when a new battery fails within months because of a faulty alternator that should have been easy to spot using a $5-$10 DVM, or even a rev with headlights.

Battery kills Alternator Alternator kills Battery It's a vicious cycle Oldspark, your not thinking like a capitalist. If you sell someone a new battery and their bad alternator kills it then you can sell them a new battery all over again at which point you point out that their alternator is defective and damage to the previous battery is not covered under warranty.

LOL - where's the Like button?! Alas I don't act like a "greedy" profiteering capitalist, but I can think like one. I admit my naivety thinking the y2k bug situation was the result of unforseeing idiots, but since then I see most possibilities for various gains. However I'd like to add that IMO batteries do not kill alternators - except for badly designed and substandard alternators. I have oft written about my experiences with Bosch alternators and I have heard similar of certain GM alternators. But in general alternators should be self limiting. Only weak power rectifiers will blow under transients or heavy loads (eg, the IMO bullsh spouse tale about keeping jumper batteries connected for a while ins NOT bulssh for Bosch) and rewound higher output alternators often burn out under prolonged overloads. In my dealings with typical Jap alternators, my only fail was the unsoldering of the sense diode in a Hitachi after 1 hour of using the starter motor and a 2nd battery with winch to pull me out of a bog. I have seen a wrongly labelled Massey battery repeatedly reverse connected to an old 25A alternator (also Hitachi) without even blowing its diodes, and copious instances powering multiple flat batteries or collapsed batteries without alternator damage. (Sure - 3 month old Optima batteries etc may have extensively burned the (rear of the) car, but the alternator was fine.) Pardon me for using this as a segway to my alternator propaganda, but I'm somewhat tired of substandard alternators causing misunderstanding. Then again, there are those that continue to say how bad grounds or high cable resistances or bigger batteries cause "a bigger strain" on alternators when in fact the opposite is true. (Seriously - how can a higher resistance aka LOWER CURRENT load cause HIGHER alternator output? As to whether a higher output constitutes "a strain"... Well, yes, it may blow crap alternators, but "strain" a self limiting (IMO) normal alternator?)

oldspark wrote: Pardon me for using this as a segway to my alternator propaganda

I can't address all that but I will say that batteries that go bad and develop internal shorts will overheat an otherwise good alternator as it tries to charge the battery that has a short. High resistance and oversized (or very depleted) batteries are also an issue. Oversized/depleted batteries like an internal short can overheat the alternator which at the very least will shorten it's life. And high resistance affects voltage sensing which screws with the alternator in it's own way.

Again I can only repeat what I said above. I've had alternators at full output even way below their regulated output (eg, down to 6V) without blowing - nor should they. Even mine lasted one hour but that was not a driving situation besides which it needed merely a resolder - nor blown windings or diodes. A good alternator is like a properly designed synchronous machine - it should be self limiting and its transient & sub-transient responses can be calculated and tested. My Bosch could not handle removing the jumper battery immediately and a later Bosch couldn't handle a collapsing battery (probably ~10V), but I am talking about good alternators, not weak crap like those Boschs.    As to high resistance blowing an alternator - how? An infinite resistance or 1MOhm or 10Ohm will blow an alternator? Note that I am not talking about bad grounds for external-regulator alternators, I am talking typical modern internal regulated alternators. But even if external with a bad ground or high resistance sense, it might blow other electrics, but the alternator itself should not blow - its diodes are likely to handle the higher peak voltages.

oldspark wrote: Again I can only repeat what I said above. I've had alternators at full output even way below their regulated output (eg, down to 6V) without blowing - nor should they.

I'm just going to give a swift and broad answer to all of that. Alternators are not meant to output at full-capacity for 100% duty-cycle. "Down to 6V" I don't know what you getting at there, in automotive the car won't even run if the electrical system goes that low, non-running car = non-spinning alternator = non-charging alternator = Zero output voltage from alternator. Also your reference to 25A alternator, I know not of any modern car that has such a low output capacity. Basic motorcycles I've seen with such capacity but again they are "basic" and most don't even have "alternators" but instead stators. Bigger bikes with electrical amenities like honda goldwings have alternators that put out more than twice 25A. I reiterate 25A is exceptionally low on a motor vehicle.

Maybe I need to rephrase my terminology. Maybe I am used to working with invincible or indestructible alternators that essentially only fail thru normal aging. Maybe I'll call them Japanese alternators? Yes, 25A alternators are uncommon these days. This was a 45 year old Japanese alternator whose ground & B+ (+12V) were reverse connected to a new 12V battery circa 15 years ago. So 45 year old silicon rectifiers sized for a 25A output withstand reverse bias shorts whereas 1980s and later >100A alternators can't even handle supplying post-jumpstarted batteries. Sure, the reverse bias was short term - maybe up to a second or 2 each time - but I doubt those nee-bad alternators would handle that. I doubt the extra resistance (if any) of the older winding would account for the behavior. Maybe it was simply Jap overdesign which was easier for 25A outputs than 100A outputs 20 years later, but with SCRs that handle thousands of Volts and thousands of Amps, I wonder why alternators don't something better. (Capitalism perhaps? ie - intentional bad or cheap design?) 6V... My car not only runs at 6V, it actually cranked and cold-started with a battery voltage of 5.2V. And yes, it is a 12V system using OEM equipment (admittedly 1985 to 1990 electrics fitted to my 1965 vehicle). However my point was that I know of alternators that continue to provide power to collapsed battery systems. Now whilst I question who could possibly do that and how the heck did they not pick such a fault unless it "just" happened - noting I consider it essential to have a dash voltmeter else good voltage alarm system - however I have told of one dude who replaced a faulty 3 month old Optima with another Optima. [ FYI - He complained of low alternator voltage. I immediately suggested he check his battery. 3 pages later he replaced his 45A alternator with a 75A and the problem was solved. He was back on the 4th page with the same problem. Luckily before any 5th page he replaced his VERY HOT Optima. It turns out the new Optima had 2 collapsed cells - hence nominally an 8V AGM - so it was absorbing up to (say) 300W as pure heat until alternator voltage started collapsing. Ped?: I assume therefore his 75A alternator was the Jap alternator and not the Bosch alternative also fitted to the particular donor car; a Nissan N13. His OEM alternator was a 45A Jap with external regulator. ] Anyhow, in the above and other cases the alternators were saturated for extended periods and did not blow. Maybe you are correct with your statement...

catback wrote: Alternators are not meant to output at full-capacity for 100% duty-cycle.

But I am talking about alternators that do, or at least do so far far longer than the "weak" or bad alternators I refer to. I guess failed capitalists can make good alternators?