Is 12 volt light bulb discharging really bad?

There are smart dischargers in the RC world. Strangely, they all have really small discharge current capacities, often much smaller than their charge capacities, so you end up watching grass grow while discharging your modules. Only reason I can imagine is they don't want to build a bigger package/load resistor/heatsink combo.

A 12 volt light bulb under the control of a smart discharge circuit would seem to be a fine thing, and I'm not sure why I can't remember reading about any such thing.

-Chap

 

If you're going to do something, I say do it right. You can buy programmable loads. I have some four quadrant SMU's that allow me to charge and discharge using voltage or current.

A Keithley 2657A can do up to 3000V, source or sink. Can also do loads up to 2KW pulsed, 200W continuous.



If you don't have the right tools, you are most likely better off just leaving the battery alone. It is not something to play with, it WILL kill you if you don't know what you're doing. High voltage DC doesn't behave as nicely as high voltage AC like in the walls. It doesn't give you an escape route 60 times a second...

 

That's a good old meme that keeps making the rounds, but there are a couple good reasons for trying to slow it down. It's got both of the features that can make a meme especially pernicious: (a) it has what seems like a plausible basis (the many zero crossings of 60 Hz AC), and (b) it gets the facts exactly backward.

The reason the seemingly plausible basis doesn't actually matter is physiological: muscle fibers need more than a 60th of a second to relax anyway. Going back to 1969 work by Dalziel and Lee, it's been known that AC, in a frequency range from 10 to 400 Hz, is the most effective for putting muscle fibers into tetany ("can't let go").

For anybody who's interested, I've done some looking around for easy-to-read papers on the various factors in electrical injury and the nicest one I've found so far is here.

None of this is to say that you shouldn't be careful around your DC battery. You should be very careful. You just don't need to think it's any more dangerous than 200 volts AC would be.

-Chap

 

I really don't want to insult, please don't take it that way, but it really is one of those "if you have to ask, you probably shouldn't do it" areas.

If you are using a standard lightbulb you are just creating a resistive load. For instance a 100W tungsten filament oldschool incandescent bulb has a resistance of about 9.5 ohms when cold and 144 ohms when hot and lit up. If the pack is 230V, you are just discharging at 24A when you first connect it to 1.6A after a few seconds. The resistance doesn't change with relation to the pack voltage, the discharge current does. As the voltage drops, the current drops for the same R. Take note of Ohm's laws: V/R = I . As V decreases and R stays constant, I must also decrease.

So to your question of "discharging at a different voltage than lightbulbs", it doesn't make sense. You can of course discharge by using a voltage that is lower. An "infinite" amount of current will flow from the higher voltage to the lower voltage until they are at equilibrium but in practice wires and connections have resistance and then you just get melting wires as "as large a current as the copper can physically take" transfers back and forth between the 2 voltage sources until they are equal or one explodes.

Using various wattage lightbulbs (like a 40W, 60W, 100W, 150W, etc) will adjust the R and therefore the I. Which maybe is what you were asking?

Again, this is not a project to just try it out on and see what works. Also since your pack is operating normally now, you have a big chance of ruining a perfectly good pack that could last another 7 years for no gain. There is lots of data on this forum showing that some batteries are down to 20% or less of their original capacity (meaning 80% of new is gone) and the MPG hit is 1-2mpg. Worst case 2mpg is 4% which is pretty insignificant when you can do better than that by just slowing by 5mph on the highways... Prius + big batteries vs. Prius + small batteries makes almost no difference. The fact it has any battery at all is where the magic happens.

Go do an experiment. Seriously. Take a ice cube tray from the freezer and fill it up so that every square in the row is at the exact same level.

Filling the entire row with water by only having one input (water hits "cell 0") and one output (excess water flows out of "cell n") is hard. If you go fast, you get erratic results. If you go slowly you have better luck. If one in the middle gets higher than the others, the only solution is to drain all of them a little bit then refill them all again. Lots of cycling.

Filling them one by one you can go as fast or slow as you want and if you want to adjust the cell, you can do it immediately.

Hopefully you can see how this analogy applies.

 

HI Tommerdo.
When you can easily hear the hv battery cooling fan especially at a stop means hv battery is very overheated..
The hv cooling fan has 6 modes/speeds all are varaible speed. increasing rpm the faster you drive and decreasing as you slow down..
At modes 1 through 3 the fan is very quiet and turning very slowly while stopped at traffic lights...
Desending 1500 and 5000 ft elevations will overheat (fact) and overcharge (my opinion) the hv battery. You should be using B (engine brakeing) gear for downhill trips. This B gear/mode uses motor/generator#2 to spin gasoline engine via motor/gen#1. to burn off excess generator charge and save friction bakes as well... If I'm decending large moutains I also like to turn on headlights and air to medium high to burn off excess energy comming from gen2 as downhill B mode doesn't bleed off all the excess energy by itself.

I use the torque app (which runs on android phone) from the google play store and a blue tooth obdII wireless diagnostic adapter to monitor hv temperature. cooling fan voltage, battery current , voltage and 13 of the paired hv battery modules voltage, and there internal battery resistances, and cell voltages differences. As well as its ability to monitor about 50 other prius parameters.. I also use torque app to manually control of hv battery cooling fan...

When the hv battery temp reaches about 108 degrees the system starts current limiting.. My untinted prius sitting (turned off) for 3 hours in the las vegas summer will reach 122 degrees and wont cool easily even when if I force cooling fan to mode 5...if driven at this temperature the hv battery after the next shut-down will always self discharge to two bars (I believe hv ecu discharges it for protection) within 1 hour of sitting (car off).

At eight bars of charge when 80 degree outside the hv battery will begin overheating.. The prius doesn't get very good mileage in mountainous areas...As the climb begins the fully charged hv battery can only provide about 3 minutes of electric motor assist then your mpg is more like a conventional car... when descending the battery will fully charge in three or four minutes (eight bars) after that it is overcharging/overheating.

When mountain climbing try to keep speed up to 50 mph or above. battery will not discharge below 58% (5 bars) while maintaining 50 + mph. You might want to find out if the hv cooling fan has ever been cleaned..
also for additional cooling set passinger airconditioner vent pointing to rear battery intake grill. and also open air conditioner intake to outside air (nonrecirculate) . This forces hot battery cooling exhaust out the back of the car..

I hope all this is not to overwhelming... But you should get many years of hv battery use if you can avoid 8 bars by running accessories and B mode while decending large hills...

 

[
QUOTE="Tommerdoo, post: 2252912, member: 137750"]Interesting. I've never heard anyone tell me to avoid 8 bars. I'm still learning about the whole charge/discharge thing. I was always under the impression that when I parked the car after driving (coming down the hill) I wanted to have a nice topped off battery (as full as possible) so that when I drive the next day it would help me get up the hill (which as you mentioned, the strength is only 3 minutes of charge or less and consequently most of the time my car only gets several hundred feet up the hill before draining to one bar). Not sure how long the car should take to drain from green to pink but it seems that it drains pretty fast going up the hill here.
Interesting about the torque app. How much is the dongle for that? [/QUOTE]

If hv battery is cold 80 degrees or lower when starting your decent 8 bars may be ok..The 8 bar no no I talk about is temperature dependent.
If hv battery starts at 100 degrees before your decent and if you park the car immediately at the bottom the battery tempurature will increase probably 15 more degrees while sitting...
How fast are you going uphill when you have only 1 bar of charge? must be 40 or below mph?

I've bought the cheap chineese ones anywhere from 8-15 dollars...The only problem they all have the same blue tooth address.
The torque apk. has trial version with less features... the pro-version is around 5 dollars..

 

Hi Tommordoo..
I have been doing similar test from the first day I bought the car new till now. However my test doesnot put the car in drive.
In drive with foot off brake and parking break on. the system will pull 3 to 5 amps. depending on how level the prius is..
With everything off and 12volt batttery fully charged and not in drive the system will pull about 1 amp from the hv battery..
Manufacture clams the prius never charges above 80% and never lets is discharge below 40% thats 40% of battery capacity.
Factor that the hv battery is rated at 6.5 amps per hour (6.5ah or maybe genII is only 6ah) and only 40% of its capacity being used discharging from 80% down to 40% when gas engine starts to recharge. Anyway 40% of 6.5 ah battery is 2.6 ah capacity. Theoreticly I should be able to let my prius. system on pulling 1 amp run 2.6 hours before engine start up to recharge battery... NEVER HAPPENS...The longest time my prius could set is 20 minutes under 1 amp load this when brand new and still pretty much the same at 76000 mile of use..And every prius post on priuschat pretty much confirms my results on all prius's...

I think your battery is in very good condition as you are pull 3 more amps in your test compaired to my test and getting 13 minutes (very good).
Also note SOC is a mathmatical calculation and 7 or 8 bars left overnight will not power the car 13-15 minutes .. However a fresh charge to 7-8 bars will power for that long and probably a few minutes longer..

Also setting idle (engine off) the fuel injectors on any car will leak unburned gasoline into engine poluting the oil.
All injectors have leakage (no problem for continous running engines) the acceptable rate of injector leakage is one drop per injector per 8 minute interval..GenII prius is noted for fuel dilluted oil (mostly city driving) Not a problem when hwy driven.. Full engine warmup temperatures will burn off this fuel diluted oil .. I recomend long drive (one hour hwy drive) once a month to burn off fuel from oil..

 

Yes my test was just powering on the car and letting it sit there...or sometime just pulling into a park and timing it bar by bar. 2 to 2.5 minutes per bar is all I've ever gotton (at its best under ideal condition)...even when bran new. I bought the car new from dealer with 9 miles on it..
I re-read your post. I still think your battery is not to bad 8 bars down to 5 bars seems exactly all mine ever did without extra load of being in gear. AND YOUR TEST HAD EXTRA LOAD OF BEING IN GEAR ?

I think maybe you should read the post again that states one bar drop took 13 minute under the load of being in gear...IMPOSSIBLE unless he has plugin hybrid it which case he has 10 times the capacity of the regular prius..

When in drive and foot brake on lighty or parking brake only and you see yellow arrows on color display screen flowing from battry icon to motor icon is when the prius pulls 3 - 5 amps..
When in drive with brakes on and yellow arrows not flowing the prius is pulling about 1.2 amps (everything else off, 12 volt batt charged) ..

My test with the lightest possible load imho is the best test...All other tests with load run hv battery down to fast.. Big loads like airconditioner on very hot day (22 amps} will sometimes take two or more bars away at the SAME time (with perfect hv battery) .

The 26 battery modules are monitered pair by pair (13 pairs total) There individual internal resistances of all pairs can all be displayed at the same time with the android apk (torque).

The internal resistances are computed while battery is under load (up to just over 100 amps full throttle acceleration from dead stop) and up to 97 amps full regenerative braking... HARD TO BELIEVE. BOGGLES THE MIND THAT A 6.5 AMP HOUR CAN TAKE IT..
60 amps of charge is about the average current seen when moderately braking. but its duration is only for maybe 7-8 seconds?

Anyway internal resistance is the only true way to tell if a batter is good or bad..

A NEW 12volt 80 ah car battery has an internal resistance of 3-4 miliohms (seen with harber freight cen tek battery analyzer)..
The nickel metal hydrid AA (2 ah) rechargable batteries purchased at walmart, kmart, target, etc brand new show 50 milliohms (with opus batt analzer/charger/conditioner)..
The prius nickel metal hydrid 7.2volt paired modules show 18 milliohms brand new at 70 degrees farenhight (with torque apk).
Mine (prius 76000 miles) which have taken alot of hv battery abuse. run from 23milliohms when cold to 29milliohms when hot (120 degrees)..
And I will tell you and everyone reading this. the prius batteries are continously balanced by hybrid ecu! (easily seen with torque app displaying high and low voltage module pairs...(high and low voltage pair number changes every second )

I could drain a 7 bar charge when new with airconditioner running 75% full. On 115 degree day at a traffic signal in only 2 minutes.
The airconditioner running full on pulls about 22 amps...
But normally I run at say 20 percent airconditioning only pulls 5 amps at 99 degrees farenheight .At 20 % air it can run 5 to 7 minutes at traffic light without engine starting to recharge the battery...

All my testing watching and timing bar by bar discharge shows no consistent results... SOC while charging and discharging (under high battery temperatures) imho cannot be calculated accurately with the prius software . SOC in only an estimation (usually pretty good) but not in high battery temp. situations).

 

I like the torque apk because of its portable-ness. I leave my blue tooth obdII pluged in continously.. Before I had bluetooth with torque I used scanguage which only allowed 4 gauges at a time to be displayed (very usefull but Couldn't display all data) and the scanguage was also connected perminantly... I won't drive prius without my telemetry (no fun without it)..
PC may even read more data than torque apk but may be combersome (ok for noncontinous use).

 

Tommerdoo,

Tell me a little about your daily mountain climb (road discription).
Are there traffic signals that stop your climb? (accelerating stopped prius on a steep incline takes alot of battery (traction) power to get up to speed).
What is the speed limit of the mountain/hill climb? Does the speed limit change to lower speed limit sometime during the climb?

At around 40mph (level road) generator number 2 provides all the traction energy where the hv battery is not needed. Perhaps 50 mph on steep incline will be needed for generator 2 to provide all the traction energy to mg1 (traction motor/generator/constant-variable-gear-selector/overdrive-gear-selector)...

Did the previous prius owner commute on level ground?
Did previous owner drive all city stop and go traffic? (harder on hv battry)
Or did previous owner drive all higway commute? (low hv battery use)

Get yourself a good digital tire pressure guage (my talking sears guage has 1/2 psi resolution but it may be obsollet). each pound of pressure loss on my genII with orignal tires results in one mile per gallon loss.. (I seem to loose about 1/2 pound per week. uniform across all tires)

What Brand of tires does your prius have? Check priuschat for users with your tires and see what presures they use...The easier you prius will roll up hill will help.. Some people run 44 psi on the front. check your tire sidewall specification for maximum pressure.. I dont think you should run 44 psi..but some people do .. I only run 35 front 33 back on orignals... and have always got 50mph (paper calculation ) 53 mph (prius computer displayed).