Parasitic Current Draw, Batteries and Battery Tenders

Steve, nice informative paper, with useful illustrations & tables. Many thanks for contributing it to the community!

 

Well done Steve. I see no issues, with your research or recommendations. Great to see a compendium of info like this...It should a "sticky" in the technical forum, where we can directly these questions from other model forums. Seems it is a weekly question all across this site.

 

Nice presentation. Two questions though.

The first a little bit picky and merely a matter of terminology. The phrase "parasitic current" is as to my understanding not the rest current due to some electronic components still in operation and, thus, drawing current. This phrase (I believe and will be happy to be corrected) rather seems to relate to "creeping" currents due to bad wire isolation, coverage of isolating surfaces by somewhat conductive coatings etc., thus not to currents consumed by properly operating components, but truly "parasitic". It is great fun searching for such truly parasitic currents .

Second, connecting the ammeter seems to be most straightforward by first fixing the leads, one to the battery terminal and one to the cable, and then by removing the cable from the battery cable. By this it seems that at no time any interruption takes place and consequently all electronic components remain at "rest" (provided that you need not change ranges of the ammeter manually). Is there some fault in this assumption that I overlook?

Cheers, Bernhard

 

Very nice write up. because I get free electricity at the Norcal house, (solar). I have a lot of EV's and have chargers on everything. The 2011 chev truck draws 80ma. I have found that a float charge of 13.8 works good and give a good charge once in a while. Lots of problems with sulfated lead acid batteries if you do not. AGM's are the way to go if you do not have a lot of batteries to deal with.

 

Seems to be "unwanted/uncontrolled" versus "intentional" current. The former is "parasitic", the latter a simple stand-by current (like in TVs etc., or are these also called "parasitic"?). The current with ignition off seems to be stand-by current (= intentional) and not "parasitic" (= unwanted, like in case of bad insulation or even bad ground contacts). But I may be wrong and the terminology in the car sector is different from other fields.

 

Nice info, Steve. Thanks for posting.

 

float charging lead acid, (not sealed) are the most durable, reliable and stable system..AGMs are not..the same with Lithium..Lithium is very temp sensitive....large remote sites are all lead acid due to their reliability and serviceability....the charging system is the most important aspect....
also add inductance to "parasitic"

 

Ah, OK, thanks Steve for this info.

In this context, it seems to be important not only to measure the current, but to know whether the measured current is indeed as specified. If the current as measured is higher than the specified parasitic current, then you need to look, where the difference in drain goes as "lost current" (?) and get that repaired/&serviced (may e.g. be a faulty ECU circuit although still seeming to work, bad wire etc.). Insofar the measured current may (or may not) be composed of the parasitic current and the "lost current", which add up to each other.

Would be very interesting, whether there is information about the parasitic current as specified by Ferrari for the various models. I have not yet seen such information.

Cheers, Bernhard

 

Yes, that is not easy to determine because almost everyone has a different brand radio, alarm, etc. installed. My TR is ~65 mA (alarm, radio, CD player, clock), but, on the earlier models with the electro-mechanical clock winding mechanism, it's even more difficult to measure (several amps for a few seconds, then nothing for a long time, then several amps for a few seconds again, etc.).

I'd be a little more generous than Steve B. for the acceptable limit, and say that, if you've got a lot of add-ons, something like ~100mA wouldn't be crazy, but, if it was something like 250 mA or more = obvious problem somewhere

 

In case of the earlier cars with electromechanical clock winding there presumably are no other consumers drawing current with ignition off. Except if you forget to switch off the (contemporary) radio, the interior light or the hazard. Those were the long gone times when parasitic currents were zero (aside said clock, a bad battery with internal discharge currents, or bad wires/connectors).

65 mA seems to quite a lot and must be due to modern type alarm, radio and CD? What the heck does a CD player do in "stand-by"???

For modern cars it presumably also depends on silly aspects, like how often you open the door. The 599 starts all kinds of procedures and it goes whizzing and summing all around as soon as the door is opened (e.g. the injection system is pressurized). Presumably quite a few amps for some time. Open the door frequently (at a dealer or just because you love to look and/or sit in) and the battery will go down quite rapidly, I suppose. Then an average of even 100 mA will presumably be a too low estimate.

 

parasitic current draw is unwanted current draw and does not in any way include wanted unswitched current draws

in the hierarchy of current draws on a car there is switched (turned on / off by key switch, unswitched ( connected directly to battery ) and parasitic current draw

wanted accessories ( alarms, computer memories, locks etc ) are not parasitic and not combined with parasitic draw in the standard nomenclature about circuits... one can speak in terms of total unswitched current draw which then would include the wanted accessories that must be powered in determining an un switched power audit... unswitched power is the universally proper term describing what you are trying to explain

 

AGM batteries are very good, but have an "Achilles heel"... they do not like to be left in a discharged state ( like most batteries ), lead acid batteries are more forgiving when having been "forgotten" in a discharged state. Especially important on Ferrari not on battery maintainer and subject to battery going flat. The AGM like hard use and deep discharge followed by immediate recharge to 100% but must not be forgotten left flat.

 

...only if recharged to full levels without delay, the AGM are robust and withstand many cycles which is what they are designed for...

a battery is considered discharged at 10.5v

 

another thing about low level of charge in batteries... they can burn up windings

starters and other robust motors generally are dumb and don't have protective circuits to only accept power that is in spec... all they know is grunt ( watts )... what they don't get in (good ) volts they make up in current ( ampere ) ampere generate heat, starting a car with a weak battery, the starter can get very hot and fail (burn up )the windings from the extra current flow... one must be very careful with extended attempts to start ( heat build up )... I guess it could also be extended to the F1 pump motor ( been recently reading about their motor failure ) as the pump motor is getting out of spec power

 

Thats what I had thought as well. Then the measured current is the "unswitched current" + "parasitic current" (if any). Such "parasitic current" (in the sense of unwanted/uncontrolled) can only be identified if any and all "unswitched currents" (intended consumption by radio, alarm etc., "stand-by") are known.

 

I would agree with that. I have never come across the use of the term parasitic in this context although a quick Google search indicates wide (mis)use of the term. Parasitic current in electronic terms refers to AC current being wasted by induction from the conductors into other parasitic conductive elements.
The terms Standby Current or Residual Current are more accurate. The systems using this current are not parasitic (at least not the ones I design )

 

There is a good portion of the paper that covers basics. FWIW I have found that the two most popular errors with battery selection is 1: Physical dimensions (the best battery starts with one that actually fits) and 2: Positive and Negative terminal type and locations. Might be worth a mention. Also, I'm fond of Quiescent current (Iccq) but I'm an old timer. Good job.