Series/Parallel cooling loops

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Series/Parallel cooling loops

Post by xp677 »

Hi guys, I was going to ask about this in the "EV car conversion hardware" thread, but my post got a bit long and specific, so here's a thread about it.

One of the goals for my EV build is to have an efficient cooling system. I am limited on battery space (and therefore range) already, and I am using drivetrain components well outside of their rated capacity as far as cooling goes (the GS450h motors and inverters were never designed for continuous use as traction motors).

I wanted a variable system that will let me:
  1. Cool the motors when required
  2. Heat the cabin when required
  3. Recycle the motor heat to heat the cabin.
For the first two, it's necessary to have two cooling loops. I don't want to heat the coolant for the motors using a PTC heater, and nor do I want to pass my PTC-heated coolant through a radiator (as that would cool it down again).

For my third point, I would need a single cooling loop, with the motors sending their warm water to the heater core.

Here is the design of my cooling system. It contains two valves which can separate the coolant into two loops, or pass it through as a single loop. I've included pictures of the two "states", series (one loop) and parallel (two loops).

Complete:
Image


Series:
Image


Parallel:
Image

Note that for the "series" setup, the secondary pump and heater would not run.

For completeness, here are the components I currently have:

Main pump - Pierburg CWA200
Secondary Pump - Lexus GS450h auxilliary coolant pump
Valve - BMW X5 dual valve https://images-na.ssl-images-amazon.com ... L1500_.jpg
Heater - Chevrolet Volt / Ampera heater

Note that the coolant valves are not the A/B type, they are two separate valves. This is the flaw in my system. To change states, I must switch 4 solenoid valves, and in either state, I must have two solenoids energised at all times. (in my diagrams, I have named the solenoids A, B, C, and D). this is inefficient! The pipework is a nightmare and I'm not sure if I can plumb this in the space I have.

What I'd prefer is a true "series/parallel" coolant valve. These used to be common in US cars in the 60's and 70's:

Image
Image

This would be an ideal solution!

Image

The question is, where can I find these valves? Has anyone come across an electronic controlled variant that isn't $200 in the USA and won't ship to the UK? Are they used in any EV's? My early searching says no, but often the "cooling system" diagrams of EVs aren't all that specific.

Most of the ones that I can find these days are cable or vacuum operated. I'd prefer not to use these as it means fabricating an actuator for them.

For reference, I am using 19mm ID hose for most of my cooling system, but the "Lexus" parts (inverter, motor, secondary pump) are 16mm ID.

Also, since people always seem to ask about my flowchart software, it's online at http://draw.io. Great for quick basic plans!
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Re: Series/Parallel cooling loops

Post by xp677 »

One valve I've found is this one:

https://www.ebay.com/itm/Electronic-Byp ... SwTiVb~F2h

The downsides?

Around £150 landed when you include fees and taxes.

5/8in (16mm) outlets.

A proprietary controller which looks to incorporate a 5k potentiometer for control, and a 5-wire connection to the motor (which may be for feedback, or may be a stepper motor). My control board (which is complete) can operate up to 5 channels of coolant valves by pulling down to GND via MOSFET, this is suitable to drive a solenoid valve, I can't see me being able to control this using it.
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Re: Series/Parallel cooling loops

Post by johu »

Not sure if my unconcerned approach is of any inspiration to you, but maybe it helps: The radiator I'm using used to be a heater core. As such it has a valve to block off flow. When blocked, water has to go somewhere else. The latter being the cars actual heater core on the end of the professional garden hose.
Maybe it's easier to find an on/off valve than a toggle valve. Y-adapters are an easy (and cheap) find on ebay.
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Re: Series/Parallel cooling loops

Post by Bratitude »

I pulled a 3 way valve from a Prius along with a pump for cheap. it’s a gear actuator with a encoder for position. mechanically, it designs to
slip if u just continually power the motor.
https://bratindustries.net/ leaf motor couplers, adapter plates, custom drive train components
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Re: Series/Parallel cooling loops

Post by MattsAwesomeStuff »

This is something I think is rare to see documented, perhaps because it's a "loose ends" type of thing which only happens when people get their drivelines built and batteries installed. And then once the car is running, "nothing is as permanent as a temporary solution that works well enough". Or, perhaps, just lack of motivation to return to forums and document things. I've been scratching my head about this kind of stuff lately too, good to see some discussion on it.

I'm not overly familiar with diagramming standards, but, it looks to me like in your "complete" diagram, you're forced to use the radiator, no? Shouldn't the loop feed back into the inverter, rather than the radiator? Else how does the system add hot fluid to the secondary loop with the cabin heater?
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Re: Series/Parallel cooling loops

Post by xp677 »

With the system in "series", the warm coolant would flow through the heater before the radiator. So the radiator would still have a cooling effect after the water has passed through the heater. Maybe this means it's not really worth doing? My goal is to recycle at least some heat from the motor, if all it costs is an extra valve.

My main priority is to keep the motor and inverter cool, however the pump and radiator chosen are for car engines, so are likely overkill. This may mean that the water temperature will never really rise much above ambient temperature.

Another advantage to the wingle system is that it requires a single reservoir. If I had a permanent second loop for the heater, this would need a second reservoir, etc.

I realise that I never drew a reservoir on the diagram. In reality, it can go anywhere, wherever is highest.

I'm still trying to track down a compact reservoir with 19mm hose fittings. The Chevrolet Bolt EV one looks perfect, but again, it's not available in the UK.
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Re: Series/Parallel cooling loops

Post by rikohm »

Substation 1 has one tank and two systems for now...
one_tank-2.jpg
I had it in series first but didn't get enough heat from motor and inverter to make a (positiv) difference on cabin heating, they more likely acted as radiators and made the heater work harder...
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Re: Series/Parallel cooling loops

Post by xp677 »

Thanks for the input. I suspect that the same will be true in my system, and that a "series" configuration is not of value.

There is a good video here which discusses the Bolt EV cooling loops:



Note that even in the Bolt EV, which is designed for long range and economy/efficiency, they still have a loop for cabin heat.


I am interested in your reservoir setup, there are a few things which confuse me.

How do you bleed the system without water actively passing through the reservoir? How do you release trapped air?

What happens when both pumps are running? Is there a transfer of fluid between the two systems?

I can't imagine that this system, which is two loops that share a tank, would function properly unless there were valves of some kind to prevent unwanted flow of fluids.

I do, however, love the fact that you're using a diesel heater. That makes a lot of sense, especially in Scandanavia. It is clever to not use battery power when diesel fuel can do the job with much lower space/weight requirements. And I imagine the car is still classed as a pure EV for registration/tax reasons:)
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Re: Series/Parallel cooling loops

Post by xp677 »

MattsAwesomeStuff wrote: Mon Feb 10, 2020 11:46 pm I'm not overly familiar with diagramming standards, but, it looks to me like in your "complete" diagram, you're forced to use the radiator, no? Shouldn't the loop feed back into the inverter, rather than the radiator? Else how does the system add hot fluid to the secondary loop with the cabin heater?
Looking at it from this perspective, I imagine and "ideal" EV cooling setup would be like this?

Image

I imagine the ideal solution would have as few changes to the loop as possible. The picture above shows two states:

One where the motor is below a temperature where it requires active cooling, and as such its heat can be used to assist an external heater. The radiator is bypassed

One where the motor is above this temperature, and the radiator/radiator fans are required to cool the motor. At this point, water temperature would not be high enough to provide cabin heating, so a separate loop is required.

What have I missed here? It's an interesting challenge.
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Re: Series/Parallel cooling loops

Post by xp677 »

Here's a first look at a complete system which could achieve this:

Image

Is this it? Is this the most efficient motor cooling/cabin heat warming cooling system? Is there a solution which uses fewer active valves (this system uses two valves, which have one input and a selectable "A/B" output)? Can we use check valves to reduce our valve count? Or maybe swap to single (on/off) valves?
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Re: Series/Parallel cooling loops

Post by celeron55 »

I can confirm motor/inverter heat is useless for heating the cabin. I tried. Airflow will cool them before they get hot enough. Maybe if you wrapped them in insulation but that would be insane. City driving losses are too small even then. You need at least like 2kW for any actual heat. 500W will barely clear some fog from the windshield.

Also having a separate cooling and heating loop bled into a single reservoir is very difficult. I'm using a system like that, it's not fun.

My current setup has three loops: one for heating, one for the battery and one for motor/inverter/charger cooling.

The heat loop is connected to the reservoir, the cabin heat exchanger and two heaters.

I have solenoid valves that make it possible to run the battery loop either through the radiator, through the heat loop or through a bypass hose.

The motor/inverter/charger loop always runs through the radiator. Thus it gets bled into the battery loop when the battery is being cooled.

After losing coolant, the system is bled by cracking open hose connections at various places and running solenoid control in different modes. It takes a considerable amount of time.

After being initially bled, programmed solenoid control passes enough battery loop coolant into the heating loop which is connected to continue getting rid of remaining bubbles. The solenoid is positioned in such a way that if there is air in the battery loop, the air will enter the heater loop along with coolant when the solenoid is open that way. The same thing happens for the cooling loop by collecting air into the battery loop via the radiator.

Every few minutes my controller will set the battery loop for cooling for a few seconds, and then set it for heating for a few seconds, just to slowly transport bubbles into the right place.

As someone will probably ask: In the heater loop I have a modified 1.5kW DEFA coolant heater (removed the AC specced explody bits and added a temperature sensor) and a 4kW diesel Eberspacher in series. The latter has an integrated coolant pump, and I have another pump just before it at the lowest point of the loop. This system is sufficient in Finnish weather, albeit you do need much more than a t-shirt at -25°C. It's a Toyota Previa after all - lots of interior space and huge windows. The DEFA is used for automatically heating the battery to 0°C prior to charging. The battery loop has two pumps in series to generate enough pressure for 4 parallel 3 series tesla modules.
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Re: Series/Parallel cooling loops

Post by sfk »

celeron55 wrote: Tue Feb 11, 2020 11:34 pm I can confirm motor/inverter heat is useless for heating the cabin. I tried. Airflow will cool them before they get hot enough. Maybe if you wrapped them in insulation but that would be insane. City driving losses are too small even then. You need at least like 2kW for any actual heat. 500W will barely clear some fog from the windshield.
This clarifies things a lot for me. I think this indicates the motor/inverter needs a system that can cool and possibly the battery needs one that can cool and heat (depending on your climate). Cabin heating is best considered separately.
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Re: Series/Parallel cooling loops

Post by celeron55 »

I'd consider battery cooling important only if a vehicle will have a charging rate higher than, say, 0.15C, as it's really only fast charge/discharge cycling that will accumulate enough heat to be a problem, unless you regularly have like >30°C daily average temperatures.

Climate has less to do with cooling, but more to do with heating. The most important thing is whether you'll have below freezing average daily temperatures - most wouldn't risk charging lithium ion batteries below 0°C.
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Re: Series/Parallel cooling loops

Post by MattsAwesomeStuff »

most wouldn't risk charging lithium ion batteries below 0°C.
Is that a concern for modern lithiums, or just LiFes?
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Re: Series/Parallel cooling loops

Post by jnsaff »

AFAICT only LTO chemistry can be safely charged below 0C without risking reducing battery lifetime. There is a puzzle in my mind about Nissan who do have battery heating but according to Mr Weber Auto it only works somewhere in minus teens and I must be missing something.
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Re: Series/Parallel cooling loops

Post by sfk »

I think the battery heaters in Leafs were only fitted for cars sold in certain territories. It wasn't standard.
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Re: Series/Parallel cooling loops

Post by rikohm »

I am interested in your reservoir setup, there are a few things which confuse me.
How do you bleed the system without water actively passing through the reservoir? How do you release trapped air?
There is a bleed vent on the top connection of the heater core, but yea, I have had to bleed it a couple of times before I got rid of the air. Inverter circuit bleeded itself.
What happens when both pumps are running? Is there a transfer of fluid between the two systems?
Only from thermal expansion.
elec_eq.jpg
I can't imagine that this system, which is two loops that share a tank, would function properly unless there were valves of some kind to prevent unwanted flow of fluids.
It's only a schematic view, maybe easier if redrawn?
top_up.jpg
There is a difference between the schematics and the car, I removed the radiator to have room for the diesel tank for the heater... Have to fix that before summer..
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Re: Series/Parallel cooling loops

Post by joromy »

I use a peltier heater/cooler, with two water loops/pumps.
I can run it from the EVSE in AC mode only, or while charging.
It can run on DC when not plugged in.
Using a microcontroller with temp sensors, one for outside temperature compensation.

It works surprisingly well, when it's 5-6C outside it uses about 80W, total, to keep battery temp at 18C
At max it can increase the temp from 5C to 18C in 30min. 1500W pluss added heatpump effect.

It may seem complicated, but I don't need a heat exchanger or solenoid valves to utilize the heat from charger, motor, inverter and DC/DC.

Have some more description here:
viewtopic.php?f=16&t=221
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Re: Series/Parallel cooling loops

Post by Kevin Sharpe »

Thanks for sharing all your experience... would be great to have a topic on cooling/heating at a future "Open Inverter World" show ;)
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Re: Series/Parallel cooling loops

Post by Igor »

This article has a bit of detail on the coolant flow in the Tesla Model 3: https://www.gizmodo.com.au/2018/12/the- ... -solution/
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Re: Series/Parallel cooling loops

Post by arber333 »

I use two loops with own reservoir for motor inverter cooling and heating. Order of business is:

Reservoir
I (Y connection)
Pump - inverter - motor - charger - heat exchanger
and back to pump... I will use charger when stationary and one Arduino DUE will run the pump relay. Bleeding is done at exchanger hoses courtesy of Fiat engineers. 😉
Fluid is water glycol mix 50:50.

Second loop is for heater.

Reservoir
I (Y connection)
Webasto with pump - heater core - isolated fuid container
and back to webasto. Later I may add 2kw electric heater inside 3l fluid container for those not freezing days...
Bleeding was done at heater core inlet at Peugeot specs.
I will use 100% ethylene glycol which does not expand and keeps boiling point above 150deg C.
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Re: Series/Parallel cooling loops

Post by NiHaoMike »

Why bother with hot water for cabin heat? Just use a ceramic heater core for windshield defrosting and heated seats for comfort. I suppose you could loop the motor cooling loop through a block attached to a Peltier, with the other side attached to a heatsink set in the fresh air intake.
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Re: Series/Parallel cooling loops

Post by arber333 »

NiHaoMike wrote: Sat Feb 15, 2020 3:07 am Why bother with hot water for cabin heat? Just use a ceramic heater core for windshield defrosting and heated seats for comfort. I suppose you could loop the motor cooling loop through a block attached to a Peltier, with the other side attached to a heatsink set in the fresh air intake.
Old question, but it applies nicely to my current enviroment outside... -5deg C daily and -12deg C at night.
Ceramic heater core will only serve for mild cold maybe around 0deg to demist windshield and make driving more comfortable.
When transfering large heating power (5kW) you want to use coolant. It can also conserve the heat for some time if you insulate your reservoir.
I am still considering using 12V PTC preheater element from VW Golf inside my air duct. Maybe it would be enough for those transitional days...

What are the battery out in the cold experiences from the rest of you? My car is in the garage and there were not many times i had to left it in sub zero for the night. Also battery mass keeps it from going sub zero for quite some time.
The worst experience was when i had to leave the car in the airport for 4 days. Battery was like 60% SOC but there was sub zero cold for 2 nughts in a row. I didnt have battery heated in any way at the time. When i arrived back and picked up the car i started down the ramp to accelerate on the road. Pack voltage just plummeted (to about 3V per cell) and i had to drive really carefully for like 20Km. I guess then batteries heated up enough for me to drive on the highway.
I dont know if battery heating would be of any help in that situation, because you still have to heat up the battery mass and it takes some time...

My point is, do you see an actual need for active battery heating? How would you do it and results if you please.

tnx

A
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Re: Series/Parallel cooling loops

Post by LRBen »

arber333 wrote: Wed Jan 13, 2021 9:45 am
My point is, do you see an actual need for active battery heating? How would you do it and results if you please.
I didn't bother with any battery heating on my quadbike. But I only use a 5amp charger for a 48AH battery, it's kept inside and UK weather never really gets that cold.

For the MG I'm thinking of lining the bottom of the battery box with heater mats. Mostly just to keep the worst of the chill away during the few colder nights we get in winter. Probably hooked up to 240vac while it charges and not powered internally.
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Re: Series/Parallel cooling loops

Post by celeron55 »

arber333 wrote: Wed Jan 13, 2021 9:45 am What are the battery out in the cold experiences from the rest of you?
I actually ran into a bit of a problem a week ago when I hadn't driven the car in days and outside temperature had been down to -30°C for a couple of days, altough it was actually just -10°C that day. My BMS has a strict discharge limit of -20°C because I'm a bit worried about the healthiness of extreme cold discharge to my model s battery modules, and at -20°C the modules barely give enough power for highway driving anyway.

The lowest temperature of the modules was still -21°C. As the 12V battery had deep discharged (that's my luck obviously) I had to set up a lead acid battery charger first and try to get the beat up 12V battery to have a decent voltage. Once that happened I could plug my EVSE granny cable for 1-2kW of electric heating and power up the diesel heater for an additional 2-4kW, and set the coolant system to forced battery heating. It took more than an hour for the coldest point of the battery to get to -19°C. The systems didn't like the slowly ramped up 12V voltage and were in some messed up state so finally then I had to disconnect the 12V system and reconnect it to get the main contactor to close.

One viewpoint is, from that situation a gas car probably would start right away given a healthy engine and 12V battery, but so would have mine if I had a healthy 12V battery and would've just modified the minimum temperature in the BMS a bit, or maybe implemented a manual temperature override switch.

I'll be definitely designing my next conversion with that situation in mind. If the 12V system ramps up slowly from 4 to 12V, it shouldn't go into a non-functional state. Also the system shouldn't drain down the 12V battery which is barely managing to stay alive in such low temperatures anyway. For me, there are only two options for a car in the -21°C battery situation: Either don't enforce a minimum temperature, or make it as simple as possible to heat the battery to the minimum temperature. Also, it's important to have temperature dependent charge voltage for the 12V system. 13.8V doesn't charge a -30°C lead acid battery at all.
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