[Project] Extending EV range by offsetting auxiliary 12v loads using solar

meetyg

Solar Enthusiast
Just read a bit online on the differences between continuous and intermittent relays.
In fact, most sources talk about solenoids, not relays, regarding this difference.

Anyways, although this is a high (100/200A) current relay, I would doubt it is really suitable for a car's starter.
I think car starters draw a much higher current than just 100 or 200 amps.
This is judged by the cold-cranking-amps (CCA) rating of some car batteries. These are usually a few hundred amps, not 100.
So I am hoping that this relay is just a high current continuous one.
But I will be checking this just to make sure.
I will try to power it without load for a few hours, and inspect it to see if it gets hot (or burns altogether). I will try this with a small lifepo4 5Ah battery, and will attach a 30 amp circuit breaker just in case the relay burns and shorts out.

Thanks for the info.
Better be safe than sorry...
 

Hedges

I See Electromagnetic Fields!
You can shop on Grangers or McMaster-Carr to get an idea of specs. Grangers is often too expensive.
I buy most things through eBay.

DC relays can have something called an "economizer", which allows high current to close the relay then switches to low current to hold.
A light bulb in series with the coil might do that - it is 1/10th the resistance initially, then increases in resistance as it heats up.
A PTC thermistor would behave similarly.
The 12V out from this relay could open a low-power relay that had been shorting a resistor in the coil circuit.

One that I use (100A 120VAC switching, 48V coil) has two coils in series, and an extra contact to short out the coil.

It is possible this relay is OK. 4W isn't a huge amount.
 

curiouscarbon

Science Penguin
thanks for the updates! good work on the centralized integration board 🛠

re: intermittent vs continuous duty relays:

does relay heat up when activated for more than five minutes?

could use the shunt to measure relay coil power use?

no matter what material it’s constructed of, if the outside case does not heat up noticeably after half an hour of being engaged, then even if it’s ostensibly rated for intermittent use, i personally would probably experiment with it for tens of minutes or hours at a time with a cautious eye and maybe even a temperature sensor on the relay for over temperature safety disconnect

this mcp9808 has served me well, for an unsolicited inexpensive i2c sensor recommendation if needed :) the temperature measurement is 13-bit internally according to data sheet.

this project is really cool imho!

intelligent system to augment vehicle power source with VIPV! turning sci-fi into sci-re 😎
 

curiouscarbon

Science Penguin
DC relays can have something called an "economizer", which allows high current to close the relay then switches to low current to hold.
the gigavac mx12 relay/contactor specified for 200A continuous duty, yet only has 1W and 1.4W continuous power use to stay closed. the two models with that <2W power figure indicate a control circuit to achieve the lower use. datasheet
1637090749462.jpeg
that specific model’s amp rating is overkill too, but i just think it’s neat! that 200A switched with ~1W :) maybe a diy solution will emerge someday to do this for less cost
A PTC thermistor would behave similarly.
The 12V out from this relay could open a low-power relay that had been shorting a resistor in the coil circuit.
oo neat, taking notes.. take relay, bench dc supply, slowly ramp up voltage to coil. starting from 0V, going up. every 0.5V note whether the relay has closed. maybe temperature of relay case too? once it’s closed, go up maybe 1V and call that the Activation Threshold Voltage?

then begin reducing the voltage 0.5V at a time to find the voltage that the relay opens again when the solenoid magnetic field becomes too weak. Drop Out Voltage?

finding a PTC that would start with the Activation Threshold Voltage, and then after 10-60 seconds change resistance to cause the relay coil to receive slightly above the Drop Out Voltage.. i’m not that good with ohms law to do that right now 😅

one last thing to look for when testing, if the relay begins heating up a lot when at the lower voltage, maybe the lower voltage needs to be increased to press the internal conductor harder to reduce resistance.

randomly thinking “out loud” so to speak💭
One that I use (100A 120VAC switching, 48V coil) has two coils in series, and an extra contact to short out the coil.
interesting! there’s so many different circuit topologies to handle the solenoid control, thank you for sharing
It is possible this relay is OK. 4W isn't a huge amount.
indeed; the project does technically specify an intermittent use case (only closed during certain, changing, vehicle/environment conditions)

love this project!☀️🚙🔋👍
 

Hedges

I See Electromagnetic Fields!
Congratulations, you've now engineered an optimizer! Based on a data set of one sample, under ambient conditions.

Repeat data gathering with a temperature chamber, and multiple samples from different manufacturing lots.
Perform statistical analysis and design based on 3-sigma or other desired limits.
Perform FMEA.
Don't forget that 100A load on battery might cause coil voltage to drop, causing it to open, at which point voltage rebounds ...

:)
 

meetyg

Solar Enthusiast
Thank you both for the informative replies!
One more thing to take into consideration is that a relay in a vehicle (as opposed to a static environment) would have to deal with vibrations. The conductor would have to be pretty stable and withstand vibrations and some jolts now and then.
So it should be "pressed" hard enough by the voltage to handle this.

I have started testing the relay...
It seems to start at almost half an amp, and slowly goes down to around 300ma after a few minutes. I'm not sure this relay has an optimizer though. I took you advice and connected it through a shunt.

I'll post my result soon. I want to test it for at least 20 minutes to see how things go.

For now I can say that after about 5 minutes there is a spot on the relays casing that is getting warm, but doesn't feel exaggerated.
 

meetyg

Solar Enthusiast
OK, bad news...
After 50 minutes the relay started heating up pretty bad.
The current draw went down though.
Here is how it started:



20211116_225140.jpg
Then after 4 minutes:

20211116_225525.jpg

and after 51 minutes:
20211116_234257.jpg

And here are some thermal images of the relay itself after 51 minutes:
img_thermal_1637099120761.jpg
img_thermal_1637099128033.jpg

This is worrying but also interesting at the same time. I say this because I found some very similar high-current relays on Amazon, and they were all continuous ones.

So I wonder if this is normal behavior or maybe this is really just an intermittent relay.
 

Bud Martin

Photon Sorcerer
It looks like the relay contacts have high contact resistance so it heats up, current handling rating is probably faked. Check the Vdrops between the contacts of the relay.
 

Hedges

I See Electromagnetic Fields!
It seems to start at almost half an amp, and slowly goes down to around 300ma after a few minutes. I'm not sure this relay has an optimizer though. I took you advice and connected it through a shunt.

Measure voltage at the relay too, and calculate resistance.
Temperature coefficient of resistance for copper is 0.4%/degree C, so would have to rise 167 degrees C to explain drop from 500 mA to 300 mA just due to temperature change.

Oh, looks like you do have voltage and current measurements (is the voltage across the relay, or other wiring too?)
Try the math on temperature of copper coil, see what you get.

Nice you're got a thermal imager. 88 degrees C wouldn't necessarily be unacceptable for the windings, but higher than 60 degrees is probably too much for plastic case. (would like touch-safe temperatures.)

It looks like the relay contacts have high contact resistance so it heats up, current handling rating is probably faked. Check the Vdrops between the contacts of the relay.

Was any current going through contacts in this test?
 

meetyg

Solar Enthusiast
Measure voltage at the relay too, and calculate resistance.
Temperature coefficient of resistance for copper is 0.4%/degree C, so would have to rise 167 degrees C to explain drop from 500 mA to 300 mA just due to temperature change.

Oh, looks like you do have voltage and current measurements (is the voltage across the relay, or other wiring too?)
Try the math on temperature of copper coil, see what you get.

Nice you're got a thermal imager. 88 degrees C wouldn't necessarily be unacceptable for the windings, but higher than 60 degrees is probably too much for plastic case. (would like touch-safe temperatures.)



Was any current going through contacts in this test?
No, this test was without any load.
I just wanted to see if this is a continuous relay or not.
The voltage displayed is the voltage going to the relay.

The thermal camera I have is a small device you connect to you phone. it's a UNI-T 120 Mobile.
A nice little device that less expensive than a full blown thermal camera. I'm still learning how to use it.
 
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Bud Martin

Photon Sorcerer
The pictures show two heat spots @ 88.4c (temperature rise of 63c) on one side of the relay, the relay only has one coil so it surprised me that it shows two spots of heating and one large spot at 72.4c on another side of the relay.
BTW, I need to look into the UNI-T 120 Mobile, you mention.
Is this the one you have? Thanks.
 
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meetyg

Solar Enthusiast
OK, so now I'm even more confused:
I just did a similar test to a small 40A relay. Again, without load, just to see if it heats up when on for a while.

After only 20 minutes or so this little thing was also very hot.
So either this is also an intermittent relay (which would be very strange) or my testing is somehow flawed.

The current draw on this little on is of course alot less.

Here are the results:
Starting current
20211117_000115.jpg
After 24 minutes:
20211117_002546.jpg
img_thermal_1637101616383.jpg20211117_000131.jpg


Maybe these relays shouldn't be run without loads?
 

meetyg

Solar Enthusiast
The pictures show two heat spots @ 88.4c (temperature rise of 63c) on one side of the relay, the relay only has one coil so it surprised me that it shows two spots of heating and one large spot at 72.4c on another side of the relay.
BTW, I need to look into the UNI-T 120 Mobile, you mention.
Is this the one you have? Thanks.
Yup, that's the one.
 

Hedges

I See Electromagnetic Fields!
OK, so now I'm even more confused:
I just did a similar test to a small 40A relay. Again, without load, just to see if it heats up when on for a while.

After only 20 minutes or so this little thing was also very hot.
So either this is also an intermittent relay (which would be very strange) or my testing is somehow flawed.

The current draw on this little on is of course alot less.




Maybe these relays shouldn't be run without loads?


Powering a load won't make it any cooler.
Connections to all terminals, and heavier wire coming from the terminals, would serve as heatsink and make it cooler. Try that.
 
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