12 Volt Battery Service

Actually this is note quite true again. Vacum is a perfect insulator containing no electrically charged particles which are necessry to "carry" the current. The reason "tubes" work, briefly, the metal electrodes actually "contaminate" the vacuum, by releasing electrons (especially when heated) this is what was happening when you were waiting for the tube to come on, if you actually saw some of this in work you could see they were hot red glowing (heated) ). And then those free electrons flow through the now, not real vacuum......

Skin effect only happens with AC application. Because changing current creates magnetic field which generetates an electrical field which opposes the original current... effectively pushing the current carrying electrons outward of the conductor. This is pretty complex but quite well known. The effect depends on various factors like frequency, current, and the electrical AND magnetic properties of the conductor. Like ferromagnetic iron conductor is useless over just a few kHZ ... so skin effect is not a simple phenonmena... BUT not something happening in DC. So not applicable in the prius (only around the inverters and perhaps the conductors going to the motors... where there are high frequency stuff going on). But this started out with the 12V battery terminals where this is JUST NOT happening.

Also at 60Hz home application using common conductive material this is again NOT really an issue. (But start happening with magnetic material like iron/steel !!)

 

Jeff hi
My battery is low about 4 volts and it seems when I idle for more than 10-15 minutes it stalls and goes dead...
I was going to check out the terminals first and see if that helps also.
So since you changed your battery, I was wondering if you can give me the truth:
I was told my more than one person, within the dealership and outside the dealership -
I could ruin my computer system by not replacing properly?
AND
I could get electrocuted?
Is it easy to change like on the cars 'back in the day'? or there is a protocol to follow etc?
thanks for any help you can offer
Angelika

 

Angelika if your 12 volt battery is that low it can and does affect the operation of the computers at start up, but once in ready mode the charging system will take over the work of the 12volt battery "usually at some loss of MPG". There is no truth in the fact you could get electrocuted.
When changing the 12 volt battery always undo the negative (-) terminal first and reconnect last. There is a little more work changing the Prius 12 volt battery as there is an air duct in the way that has to be removed first, otherwise the process is much the same as most other cars.

John (Britprius)

 

All right. I'm a EE, too. And I've seen your comments about corrosion and skin effect. And, yeah, I know about both of these things, part of my work is on telecom power networks.

From the top: We're talking about DC, not AC. Let's get straight about skin depth: With Maxwell's equations, one can talk about electromagnetic fields that are guided by wires or electric currents inside of wires that create electromagnetic fields. Either way is valid and the equations come out the same either way.

So: If you have an AC current going through a wire, that's the same thing as an electromagnetic field traveling along the wire. As the field travels along, at a particular spot, an AC Electric field is applied along the wire. At any instant, you'll have a positive E field at one point, a negative E field at another, and the electrons in the wire will, in response to this, accelerate away from the negative E field point and towards the positive E field point. An accelerating electron will create an electromagnetic field; after one finishes pointing fingers in various directions, one will discover with an ideal (superconducting) wire the created E field (from the moving electrons) cancels the applied E field from outside. This leads to current totally at the surface of the wire and nothing on the inside.

With a non superconducting wire that has resistivity, the fields don't cancel at the surface; rather, as one goes into the metal conductor, the field intensity drops. The skin depth is usually defined as the depth at which the external E field has dropped by 1/e (e being 2.71). Since the current is directly proportional the the applied E field, the current also goes down by 1/e. The equation defining all this (Electromag 301 course work..) is
skin_depth= sqrt(2*rho/(2*pi*f*ur*uo))
where rho = resistitivity in Ohms/meter, pi = 3.14159, f = frequency in Hertz, ur = relative magnetic permeability (1 for copper, something interesting for iron), and u0 = 4*pi*10**-7.

So, let's take copper at 60 Hz: We get a skin depth of sqrt(2*1.7e-8/(2*pi*60*1.0*4*pi*1e-7)) = 8 mm, or about a third of an inch. For 10 Ga copper wire in your house, then, the current pretty much flows through the entire depth of the wire; if you're a power company doing a thousand amps and you've got a 6" bus bar, they you may as well leave the interior 2" of the bus bar empty, since there won't be any current flowing down in there anyway, and you may as well save the cost of the copper. (That 1/3 of an inch means that the field/current is down by 1/e at the bottom of that 1/3 of an inch; if you go down 2/3 of an inch, it does down by 1/(e*e); at 2", you'd be down by 1/e**6, or 0.002 from the current at the top.)

Let's suppose that there's some 10 kHz noise floating around on the 12V wire going to the battery terminals; a quick calculation shows the skin depth to be about 24 mils.

However, we're playing with DC. With that, the skin depth is infinite; that is, there's no reduction in current flow as one goes into the material. And putting corrosion (or paint, or insulation) on the surface of the wire doesn't do anything to reduce current flow; electromagnetic fields pass very nicely through insulators, thank you, so a nice crusty bunch of surface corrosion won't slow down the current or increase the resistivity of the wire. At least until the wire gets rotted all the way through, and we're not talking about that.

Next bit: Connectors and corrosion. Hokay: Leave a bit of tin exposed to the atmosphere and SnO2/SnO is going to form, willy-nilly. SnO2/SnO is a non conductor. How in the heck can one take two objects that are tin plated, like, say, the terminal at the end of a battery wire and the battery terminal, connect them together, and get current flow?

Hint #1: It's not by cleaning the material to bright metal. Yeah, if it's really grodded up with junk on the terminals, then you might have a bit of a problem. But if one mechanically scrapes the tin so it's exposed, it's also exposed to O2 which very quickly forms SnO/SnO2. We're talking milliseconds or less here.

The trick is, tin is squishy; and tin oxide is more so. Take two tin contacts, scrape them past each other, and a mound of tin oxide gets pushed off to one side whilst the pure tin itself makes contact between the battery cable terminal and the battery terminal and mushes together. If one were to look after this process, starting at the lug on the battery, one would see Cu->Sn->Cu without a break from the copper on the battery lug through to the copper on the battery cable. No oxygen is present since the connection is surrounded by a mound of tin oxide. If the thing isn't disturbed, no air is present in there, hence the term, "Gas Tight".

Tightening the bolt on the battery lug squishes the tin a bit more and fixes the two halves of the connector in place. Get out your random Ohmmeter and you'll see resistances in the milliOhm or less range. The mush of tin oxide surrounding the tin connection is stable.. So long as it doesn't move or get chemically attacked.

This is why the 10 mm bolt on the battery connector: micrometer vibrations on a tin-tin connector can screw things up. Suppose you've got some connector, like, say, a tinned circular connector going into a tinned socket. Now, suppose the two pieces of the connector slide back and forth over a small distance, continually. The tin-tin connection is surrounded by a mush of tin oxide, to start; if it starts sliding back and forth, the mush in the middle gets infiltrated by tin oxide. Over a long enough period, one then ends up with a mush of tin and tin oxide which has higher and higher resistivity, eventually resulting in a Failure To Connect. So tighten that bolt down and No Movement Is What You Get. (This is also why a lot of automotive connectors have plastic snaps and such: To keep those connector parts from moving.)

Next: Chemical Attack. Tin Oxide is fairly stable and will keep oxygen from getting to the SN-SN contact buried underneath it, but add an acid bath and the tin oxide >will< be removed. On a regular car battery you can even smell the sulfuric acid emanating from the battery, so putting a bunch of petroleum jelly/some kind of soft, insulative spray/some kind of acid neutralizer (that's the felt washer) to keep that junk from getting into the terminal is considered a Good Idea. I've seen battery terminals so badly corroded that the wire end of the connector just kind of slides back and forth (that can't be good.. ); once, I ran into a case where the battery terminal was fine, but the acid had gotten into the body of the connector and rotted the copper battery wire loose. (A very hot terminal that actually melted the plastic battery case. Even (or especially because) the terminal was bolted down properly.

But the Prius 12V battery is heavily sealed, so the "whiff of acid" test kind of fails. I'm still willing to believe acid leaking out in minute quantities, so dumping Vaseline on the connector or that little spray bottle of red stuff sounds like a reasonable idea, at least when one replaces a battery.

But that battery is inside the body of the car. It's sealed; it's not exposed to the vagaries of road salt fog; and it's not doing major discharge cycles (which would cause heating at the terminals, which could lead to thermal stresses) to start the engine. My guess is that one application of glop per life of the battery should do the job. Although, I suppose, popping open the battery compartment and tugging on the wires to verify that everything is nailed down properly wouldn't hurt. And taking an eyeball to look for (typically white colored) corrosion products. But taking things apart? Not so much.

KBeck.

 

As long as you are careful not to connect the 12v battery backwards, no damage will be done. Connecting it backwards can do significant damage to the power electronics (called an Inverter in this discussion group).

Not by the 12v battery. The large HV battery (200 volts, 6.5 amp-hours) requires careful attention to avoid getting injured, but you will not be handling it when replacing the 12v battery.

The 12v battery is just a bit awkward to get at and there is a vent tube to attach, but the job is quite similar to any other car.

JeffD

 

Does anyone know how easy it is to change the small battery? I was told I may ruin the computer or get electrocuted.
I'm wondering if anyone has any experience with the process.
thanks

 

Jeff thanks! sorry I posted my question again (it is the first time posting online)
Today I called around and I was told they are selling the Optima or the Bosch for the Prius but the batteries are gel and do not have a vent tube. I called a local auto store, could that be accurate?

 

I thought this was just answered

Sure you can ruin the computer(s) if you connect the battery backwards (maybe there is protection like ) but you can do that by jumpstarting with wrong polarity ..

"get electrocuted" sure that is possible just not by the 12 V battery

 

If you wish to change the battery yourself there really is no problem.
Taking photographs when you start and as you remove the air duct and finally the battery will give you good references for refitting correctly.
If you fit the new battery in the same orientation as the old battery reverse polarity connection "and damage to the computers" is impossible as the cables are not long enough to get the connections wrong.
Further the terminals on the battery are different sizes so following the rule of disconnecting the negative (-) terminal first and re connecting last means it becomes obvious when connecting the positive (+ red) terminal if it is the wrong size the battery is the wrong way round the terminal will not fit and no harm is done because the negative terminal is not yet fitted.

John (Britprius)

 

John thanks
I will repeat what you are saying, to be clear, please correct me if I not right.
The air duct or vent tube? needs to be removed first then remove the negative terminal then remove positive.
Once placing in the new battery connect air duct/vent tube, then connect positive terminal, then connect negative terminal.
The air duct/vent tube I was told is not needed as the new ones are gel? I will double check.
Let's say there is an air duct/vent tube -is it connected by me, having to glue/weld/bolt in place OR is it just to make sure it vents out of the car in a certain place?
thank you for your time!

 

It was, I'm an idiot, first time posting online

 

Both the Optima and the Bosch batteries AGM (absorbed glass mat) actually liquid absorbed into the mat. They are not gel batteries and both are fitted with vent tubes if you are buying the Prius version of the batteries.

John (Britprius)

 

There is a slight confusion here with the vents.
There is a large black plastic square section vent duct about 4inches x 4inches that is in the way of removing the battery. This has to be removed first (easy to do just two bolts). This duct takes air away from the large high voltage battery under the rear floor. Do not worry you do not get anywhere near any high voltage.
There is also on the side of the 12 volt battery a rubber vent tube only as thick as your little finger. This pushes into the battery at one end and just goes through a rubber grommet in a hole in the trunk (boot for us in the UK) floor.
This carries any battery gas that may be produced to the underside of the car

John (Britprius)

 

Fantastic thank you! In your opinion, which brand is better Optima or Bosch?

 

In my opinion the Bosch is not only a better battery but also has a higher capacity and a longer 4 year full replacement guarantee.
Think of it like your fuel tank holds an extra gallon so less likely to run out. So the battery holds more charge and will hold up longer under any given load.
There are those here on PC that will disagree, but there have been a number of people here reporting quality issues with the Optima. In the UK the Optima is at such a high price "about $350" against the Exide at bout $150.

John (Britprius)

 

I'm not an EE (but my brother is). I'm a lawyer and can assure you it is possible to be electrocuted while changing the Prius battery if you are struck by lightning while doing it. Be careful out there!

 

I always get amused when a simple task like Battery preventative maintenance brings out the Engineers and Lawyers with there six inch rulers.

 

lol I know the dealership employees trying to thwart my efforts ...

 

Hey, I have a PhD in EE. Does that make my comments "Piled Higher and Deeper".

JeffD