HV Battery Pre-Heat... Anybody tried it?

Don't cut or drill the pad (rather ovbious).

Make sure that the ENTIRE pad is heating something. If there is an area of the pad that has no thermal load on it, that part will become much too hot (and its resistance will go up, making it hotter, making it's resistance go up) until all of your power is going into burning out the unloaded part of the pad.

Google "flexible surface heaters" and you'll find lots of stuff.

How about opening the battery pack (disclaimer: Use reasonable safety precautions so you don't hurt or kill yourself) and putting power resistors throughout. Attach them to the battery wall using thermal epoxy, wire them up in series, and run a power cord out.

You'll have some simple calculating to do to make sure that you get the wattage you want, and don't exceed the power rating of each of the resistors.

You could even size the resistors so that they will work at the battery pack voltage. Control them with a relay so that while you're driving, you can turn them on and use battery power to heat the battery.

Of course:

1) I'm not responsible to you if you kill your car.
2) I'm not responsible to your estate if you kill you.

Safety is your first priority!

 

What I meant is that I would charge the batteries so that the display is in the green area. Actually, overcharging the pack will make the ICE come on to discharge it. If the pack is green, I can make my trip no problem, blue is problematic. I want to insure enough charge so I can complete my short trip in EV mode.
I was also thinking of modifying the pack to allow deeper discharge. Used packs are under $500, so if the life is a little shorter, it is not a big deal. The pack now goes from 40% to 80% SOC. I would like to run it from 10% to 90%. doubling my capacity. Then, I will add a second pack to get 4X capacity. I think battery life will be 1/3 to 1/2. I haven't decided on that part for sure yet, just the small charge, if I park the car charged in the blue area.

 

This is the link to the preheat study. In it they actually test a Gen1 Prius battery as well as an AGM lead acid.

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/jte_2003-633_sw_ap.pdf

That's where the quote came from.

Charging the battery does two great things: Preheat and Charge. Enginer makes an inverter/charger kit without batteries but its not super cheap.

 

Juicy quote:

Sounds so much better than "stick a heating pad under the battery"

 

I'm all for heating the battery by one means or another if the benefit is significant enough. But how will that benefit be measured?

 

Battery preheat will improve efficiency so long as you are preheating from sub- optimal to optimal temps. There should be no debate with that.

I'm not one to quantify the savings of a mod by financial return. If I was I wouldn't have bought a Prius.

I will keep track of my daily commute and gather enough data to plot it. That's the best I can do. Short of a controlled lab test that's all any of us can do. It does pass the logic and deduction test though. If you are able to regen more efficiently and the battery charges more efficiently then you are doing better.

Quantifying it is another matter.

For more info read the link in post 43

 

Hard side. Since you will be installing this on a hard surface. From one of the hard ones:

They are not the cheapest thing going but they are adjustable and probably safer than the battery blankets because they are in close proximity to water and you and 120volts.

 

What data are you planning to gather?

 

Wow! Was it something I said?

It seems that the thread dies as soon as the subject turns to gathering actual data.

 

In my case I'm just busy with other projects. Too many pots on the stove.

I'm determined to do it though.

My current idea is to plot the regen amps, SOC, L/100 from the Graham scanner on one particular hill in my area.

There may be too much noise and variation to make a good comparison. One thing I'll have to contend with is that the battery "stores mpg" If you don't end up with the same SOC at the end your trip, the numbers will be difficult to digest. I will have to start lerning how to even out the SOC.

An A-B-A test would be impossible, really.

Ideas are welcome.

 

Thanks for responding. And I appreciate your determination.

A few questions.

1. I'm not familiar with a Graham scanner. I presume it has recording capability?
2. You are plotting your parameters to develop a baseline?
3. What is the significance of the hill in your experiment?
4. How will you correlate these parameters with HV battery temperature?
5. Is there a reason for not including initial ambient temperatures?
6. Wouldn't direct temp measurements of the HV battery accomplish your goal?
7. Evidence indicates that raising the battery temp from "sub-optimal to optimal" may require from one to three hours, depending on initial ambient temps, on an unmodified car. How will you deal with that?
8. What method are you currently considering for pre-heating?

Sorry if it seems I am bombarding you with questions but I don't quite understand how you plan to proceed.

 

I have already started to gather my baseline mpg data. ambient air, road condition, battery temps, SOC, MPG. (wind is usually not significant because of forest lined roads)

The Graham scanner is a gen 1 data display/logger which gathers data from 50 sensors and displays 4 outputs at a time.

Connects to Vehicle using Existing OBD-II Data Link Connector 3 (DLC3)
Communicates with Vehicle ECUs using ISO9141-2 and ISO14230 (KWP) Protocols
Retrieves and Displays Data on Operation of Hybrid System, Engine, Battery, etc.
More than 50 Data Items available from Engine, Battery and Hybrid Vehicle ECUs
Logs Data via a Serial Port to a computer or PDA for Spreadsheet Graphing
Retrieves and Optionally Clears Diagnostic Trouble Codes

Generously lent from Bob Wilson's "Tool library"

I was thinking of using the hill to log regen amps and SOC. I know the computer allows the battery to take more amps when it's warm so I want to see if warming makes a difference in SOC.

I have a battery warmer wrap intended for lead acid which I hope to install between the battery housing and the body. I still have to do more exploration on that though.

Currently placing the blanket on top does heat the inside of the compartment and the top of the battery as shown by the scanner but it can't possibly do a good job of even heating in that position.

I may start a new thread to document it. May be a couple of weeks before I can get to it though.

 

I'll be watching for your results. Thanks!