# Charger Control Lines



## GoElectric (Nov 15, 2015)

Hi. Greetings from Canada. Today it is-22C. 

I'm building an electric car and am wondering how I am going to control charging in cold weather. At low temps, batteries will not take a current and can be damaged (correct?). I need a charger which I can control so it does not turn on when the (battery) temp is too low. I am planning on using my own circuit to sense battery temp and turn on battery heater. But how to control the charger? I know there is an input on the charger which will turn it off, intended for the BMS. Is there a charger out there which has a low-temp control? Otherwise, I am thinking to use a relay which will take the BMS control line OR the low temp signal, and if either is high, turn off the charger. 

That should be fairly easy. But, the heater has to get its energy from somewhere, and hopefully not the batteries! One option is to run it off the 12V battery, which might be okay. The lead-acid might be able to put out enough charge to get the batteries warm enough to accept a charge and start heating themselves, even when it is cold (I'm not thinking I will run it at -20, but it would be a nice option), but it has to power the heater AND the pump. Option #2 is to draw power from the wall via the charger(?), even though it is not charging the Lithiums. I'm going to be using liquid-heating (Tesla modules). Philips & Temro has 120V Circulation Heaters. 

There are a ton of questions I could ask at this point, but will leave it there. Anyone have experience/ideas on this problem? 

Here is a link to a PP presentation on heating/cooling batteries. http://www.nrel.gov/transportation/energystorage/pdfs/aabc_presentation.pdf

Thanks a lot.

Jim


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## GoElectric (Nov 15, 2015)

I wish I could change the name of the thread now, or make 2 separate threads. 

I found this 2003 article on heating batteries via AC input. This seems like a really simple concept. Is it now used/practical? 

http://www.nrel.gov/transportation/energystorage/pdfs/jtec_hawaii_pres02.pdf

Jim


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## Tony Bogs (Apr 12, 2014)

Applying an HF AC current superimposed on a DC current to heat up the cores of the batteries isn't that hard to do with the right charger with a hysteretic control of the buck output stage. 

Another "easy" LF option is mains AC for which huge capacitors (and transformers for isolation) are needed. Very low PF.


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## GoElectric (Nov 15, 2015)

Tony Bogs said:


> Applying an HF AC current superimposed on a DC current to heat up the cores of the batteries isn't that hard to do with the right charger with a hysteretic control of the buck output stage.
> 
> Another "easy" LF option is mains AC for which huge capacitors (and transformers for isolation) are needed. Very low PF.


Ah, yes, that does sound easy. Not! Sorry, you lost me at "AC superimposed on DC." Any references I can study-up? 

I know heating batteries is off the map for many, but there must be peeps out there who have done it.

Jim


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## dcb (Dec 5, 2009)

interesting concept
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.216.8902&rep=rep1&type=pdf


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## Tony Bogs (Apr 12, 2014)

Nice Elsevier article.

At the end it is noted that a charger is needed to supply the power for the AC heating.
An on-board inverter is used to generate the AC current.

Why not use the charger as the inverter? 
If the charger buck output stage is a half bridge it can generate the ac current. 
At the same time it can generate a DC component that can be used for the cabin heater. Also very practical in winter conditions.

I will take it into account in my SiC/LLC charger design.


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## Tony Bogs (Apr 12, 2014)

Amother (recent, 2013)) Elsevier article about preheating, including an extensive discussion of AC heating in the frequency domain.
http://ecec.mne.psu.edu/Pubs/ACTA%202013.pdf

i believe that the conclusion is that AC heating at high frequencies (1kHz+) is the best and fastest way of preheating (1 minute from -20 to 20 C in the published data - graph)


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## GoElectric (Nov 15, 2015)

dcb said:


> interesting concept
> http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.216.8902&rep=rep1&type=pdf


Hi, that really helps. 

I suppose I can figure out what the "buck output stage" of a charger is, but mine hasn't arrived yet, and I'm loath to mess with it. Same with the inverter. I'm glad however if this is a new feature which you may incorporate, as it seems a good 'fit'!

I hope to see more integration of various functions like charging and BMS, for example, and this is a step in the right direction. 

There may be differences with lithium-Ion cells, but I think they are worse, if anything. The experiments talk about heating the cells in 5 minutes with 100 amps. I found this: http://www.maplin.co.uk/p/kemo-20a-pwr-power-controller-n79ql which could work for 22V Tesla modules, even if it takes 30 minutes. Easier on the cells, no-doubt. I don't see what the power input is tho.

Suggestions, please.


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## Tony Bogs (Apr 12, 2014)

I think section 3.1.1 of 
http://ecec.mne.psu.edu/Pubs/ACTA 2013.pdf
may give the solution in your case. 

It states that charging should be avoided at low temp, but not discharge. 
The internal impedance of the battery is still low enough to supply the power for the convection heating (via the Tesla plumbing and a heater). 
Discharge at max 1 to 2C (see fig. 3a).
Then it is a combination of two heating methods, convection is in 3.1.2.

Charger on/off: maybe you have already given the answer in your first post. 
AFAIK many chargers rely on an input from the BMS to signal end of charging/ do not to charge.


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## dcb (Dec 5, 2009)

there is a fairly sure fire way to ensure only AC from wall power( 240vrms here):
cap is seeing 460v peak (too much for typical run capacitors), and power factor is crap, but it is simple, the batt should not be charging or discharging.


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## Tony Bogs (Apr 12, 2014)

Yeah, that's "easy" LF option that I mentioned earlier. 
Two identical motor run caps in series, double capacity (0.002 each).
PF is really crap, you need a 240V/80A wall outlet to deliver ~ 600 Watt heat to the batteries (0.1R internal resistance).


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## Tony Bogs (Apr 12, 2014)

Twelve 80uF/400VAC (in parallel) will set you back about US$600 (new).

Seems that using battery power to heat up the pack at low temps is the cheaper (and safer) way. Is it not what Tesla does?


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## GoElectric (Nov 15, 2015)

Tony Bogs said:


> Twelve 80uF/400VAC (in parallel) will set you back about US$600 (new).
> 
> Seems that using battery power to heat up the pack at low temps is the cheaper (and safer) way. Is it not what Tesla does?


Hi. I'm not sure WHAT Tesla does, although I know the battery heater will run off of the batteries while unplugged. Good to know discharging is an option. I will get back to you, can't think right now.


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## Tony Bogs (Apr 12, 2014)

Yeah, I meant to write HOW Tesla heats up the pack (without a wall outlet).


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## dcb (Dec 5, 2009)

I think the self-powered heating probably isn't the biggest return, based on typical usage.

Also liquid cooled batteries probably have an easier time with a simple resistive heater and a pump.

So the biggest audience is probably calb/leaf or otherwise non-liquid cooled batteries.

So two main scenarios

1 you are at home, it is cold, you plug in and the wall charger (or an onboard circuit) says "hey I have to warm up the battery, and you don't have any other options from this, aside from building a fire under the pack".

2 you leave it plugged in overnight, and with a remote or a timer or?? it pre-heats the battery before you take off, perhaps with a simple circuit.

for pre-heating while driving, that could be a controller mod. Which basically motor/generates (at 1khz?) for everything under full throttle, with a net positive force, till the battery is up to temp.

So something simple that can fake out/redirect say, a j1772 before allowing the charger proper to operate, or preheat before driving, it would be the same basic controller as the liquid cooled heater, with the ac power sent to the sine wave thingy instead of a heater.

it isn't yet clear how you close the gap between lots of wall power and a relatively small amount of resistive heating in the battery though, especially critical if you are using 30 amps as a j1772 common denominator.


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## GoElectric (Nov 15, 2015)

Hi dcb, thanks for your input.

I'm not sure what you meant by: "I think the self-powered heating probably isn't the biggest return, based on typical usage." As you describe, I think the most common scenario will be when I am parked at home. 

If I turn off the charger via the BMS input, I am still thinking I would run the heater off of the batteries. Only, it would be a waste to keep the batteries warm all night. This would drain the batteries too. So, control the battery power via the charger plug somehow (which is on a timer). Then I only heat the batteries when they need to be charged. If I also had this control operated by the ignition-switch (logical OR), then when running I could keep the batteries warm too? So, I need 2, 2-input relays which can switch 120VDC with input at about that (120AC -> 85CVDC? The AC control has to be converted to DC somehow; should be able to buy that off the shelf). And I have to worry about isolating grounds, I don't want the rectified AC ground to cross-over with the battery ground, right?

The AC cycling is attractive, but I would still need a system for heating the batteries on the road, which is why I am leaning towards the DC-powered circulating heater. Not sure how you think you might alter your design, I guess you could use the inverter. 

I haven't actually located a DC circulating heater yet either... and don't know what pressure I will need. I have found a source for surface mount temperature switches tho. Just need a place to mount it INSIDE the Tesla pack(s?). https://www.cpi-nj.com/products/sna...t/ad069-spdt-spst-surface-temperature-switch/

Long way to go here - still waiting on delivery of batteries & the rest of the hardware. 

I plan to do other cars, so if you have a system you are working on, when will it be available? We should keep in touch. My other option would be a $1,500 BMS with temperature inputs and heater outputs, but I don't otherwise see the need.

Thanks again.

Jim


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## piotrsko (Dec 9, 2007)

Electric water heater elements work on DC. Unfortunately switching DC makes huge arcs and the relays are therefore expensive. I made one using a Volt mains relay controlled by a standard replacement water heater strap on controller. Good from 80 to 160 degrees. A pc multi voltage adapter powers it on either 220 VAC or 192 pack DC.

On a volt pack, you could use their heater or a car block heater. Wont take a lot of heat perhaps a 1/2 KWH to go from 20 to 80 degrees at perhaps 2gpm at 5 psi.


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## GoElectric (Nov 15, 2015)

Hey, hey, hey! Nice to hear from you, "Piotrsko." 

I appreciate the info. 

Can you explain a bit more about the controller from the water-heater? Are you saying you used that hardware to sense battery temperature and thus activate the pump? What is in there?? I was just thinking of a thermo-switch (link above). And what use is the temp range of 80-160?? Or are you using that for cooling?

A power-supply which runs off 220AC or 196DC, nice.

Yes, I suppose switching 120VDC is not the same as AC. It will just be the current for the circulating heater, tho, right? 

I have some sourcing to do for all of this. Thanks for the ballpark figures on the circulating pump. The cooling/heating system on Tesla modules is woven around all 444 cells in each module. The length of it all stretched out is almost 20 feet. Then I have six of those. What do you think?? Here is a pic of a module partially disassembled, and a pic of the cooling tube+connector. The tube is crushed at the end, but cross-section it is divided up into six rectangular chambers/sections inside.

Jim


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## dcb (Dec 5, 2009)

GoElectric said:


> I'm not sure what you meant by: "I think the self-powered heating probably isn't the biggest return, based on typical usage."


Hey Jim, let me try to clarify a bit.

If you have ac power available, use that, and don't cycle the batteries any more than necessary. 
2 scenarios: 
1. you need to charge and the pack is too cold (lithium plating), use the AC to heat it up before charging.

2. you are going to go for a drive and the pack is cold, let the wall power heat it up ahead of time.

The third scenario is when you want to heat it up when not plugged in.
My internal combustion experience (which may be wrong here) tells me to just drive it easy till it warms up for best efficiency. Sitting there idling a heater will use energy but not get you any closer to home. 

To aid in rapid heat up I was contemplating using the inverter (another name for a 3 phase motor controller) to cycle between acceleration and regen rapidly, i.e. 1000hz per toms figuring, with a bias on acceleration (so the car moves forward).

The third scenario is for when you don't have ac power or are in a hurry perhaps.



GoElectric said:


> So, I need 2, 2-input relays which can switch 120VDC with input at about that (120AC -> 85CVDC?)


There are a couple basics about electricity you need to know, i.e. ohms law, and the relationship of ac rms to peak and to dc heating valued.

volts=amps * ohms (amps=volts/ohms, etc).
power/watts = volts * amps (power = amps * amps * ohms, etc)
energy/watt hours = power * time/hours
kw=1000 watts
kwh=1000 wh

ac volts/amps are typically sinewave and measured as rms values, which is the peak value / sqrt(2), so a 120v ac signal is a sinewave with a peak value of 170v. the rms value is also considered the dc equivalent heating value.




GoElectric said:


> I don't want the rectified AC ground to cross-over with the battery ground, right?


It is less than ideal, but people do it, you need to be more careful if you do.



GoElectric said:


> The AC cycling is attractive


The concept was new to me as well, and really what I'm focused on because I have a lot of leaf cells and it is getting cold outside. I have no plans to sell anything but am more than happy to share info on what I've sorted out.



GoElectric said:


> but I would still need a system for heating the batteries on the road


Since some of us have made our own ac motor controllers, I think it is reasonable to consider utilizing that for the purpose, somehow. Still my instinct is that you should be in motion for most efficient warm-up (as measured by miles/kwh)



GoElectric said:


> which is why I am leaning towards the DC-powered circulating heater.


If I had liquid cooling, or heating elements, I totally would start there, this sinewave stuff is terribly experimental as far as I can tell. But I would still utilize wall power whenever it is available over battery power (with appropriate circuitry to avoid actually charging a cold battery).


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## piotrsko (Dec 9, 2007)

You don't say where your at, so I will hazard CONUS. Most building supply places have replacement electric water heater controllers that just strap onto the water heater tank for about $20. What ever the tank temprature is under the insulation is what the controller sets, generally 80 to 160 degrees. Most of these will be just a bimetal thermostat rated up to 20 amps on 220 Vac. This is the control circuit. They work once only when using DC.

I noticed my old laptop charger worked on either 120 vac or 220 vac. Doing the above math about RMS I get 120 to 360 VDC. Since it was laying around, I applied pack voltage and waited for magic smoke. No smoke, 12vdc out. Run that through thermostat to 400Vdc Volt mains relay. Pack voltage on relay contacts through water heater element. I have a manual plug that either uses pack voltage or 220 mains voltage depending on what I plug in. Volt relay doesn't care what it switches Ac or Dc. Play with adjustable screw on heater controller for desired temperature.

No, cooling of my volt pack is just passive 5 gallon water tank. My System only heats about 10 degrees above ambient even during hard use in the summer. I dont know what your pack gets to while running.


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