[aarossig]

I have been tossing around the idea of extending the EV range of my ELR with a supplemental battery pack in the trunk. Before you think "this guy's nuts"... well, I am a little, but I do have experience with electronics and embedded systems. A well informed nut who is well aware of the risks of dealing with lithium batteries, let alone in a 96S configuration.

To my question: what is the rating of the high voltage fuse for the APM? What else is on this bus? I understand that it is shared with the AC charger and APM. I have seen this fuse labeled #2 in one TSB. Is there anything else I need to be aware of that shares this fuse?

The basic idea for my project will be to buy/design a DC-DC converter to dump current into the primary battery pack while driving. The APM with lid removed provides an access point to the HV bus. The charge rate will be limited by the APM fuse (and wire gauge). I have read two specs on this forum: 20A and 15A. I hope for the former as this would allow a modest ~6kW charge rate (80% fuse rating, 25mph at 250Wh/mi, back of the envelope calculations).

Is this fuse replaceable without dropping the battery? I plan to fuse my experiment as well but if something goes wrong and I pop the APM HV fuse it would be best to avoid a costly trip to the dealer.

Please avoid the "not worth it" and "you'll poke your eye out" comments. I know it's cheaper to buy an EV with longer range from an OEM (I already have one). I am also familiar with the hazards of working with lithium batteries and the necessary precautions to take. Looking forward to a fun technical discussion 🙂

"Your scientists were so preoccupied with whether or not they could, they didn’t stop to think if they should."

 

[Tacoma]

How many kwhrs will your add on battery pack be?
A DC-DC allows you to make the 2nd pack any voltage you want.
Two 24 VDC Tesla modules in series would add around 10 kw and almost double your EV range.
This would need to be up converted from 48 VDC to up around 400 VDC with current limiting capabilities.
How do you plan to keep your existing pack safe in terms of possibly over charging it?
A 6 kw transfer rate would of course be 6 kwhr of energy in 1 hour.
If traveling at city speeds 30-50 mph, would mean you could probably get 2/3 of a 10 kwhr pack, less if going highway speeds.


Kind of big and heavy, but have you considered a parallel string?

 

[Steverino]

Here's a guy who did that:
http://gm-volt.com/forum/showthread.php?258793-Volt-with-130-140-km-(80-85-mile)-battery-range

Please post pics of the project!

 

[Guest]

Adding a parallel battery bank is possible for any EV. The main issues are the BMS and the cooling. Most Li-Ion systems use the voltage to determine capacity, so if the Volt's or ELR's GOM uses the battery voltage to determine range, it will be correct most of the time, and the range will be higher as expected. The onboard motor/generator and AC-DC charger can handle the extra battery, too.

The BMS is harder to add to the Volt's system. You would add a new BMS (easier to do in hardware) to monitor just the added battery.

 

[mpmoore1979]

To answer the question, its a 15amp fuse located in the high voltage battery.

There is nothing else in the circuit but there is a diode on the contactor this circuit is connected to the rest of the high voltage system. The diode may cause this not to work, will not allow currant to flow back in to the battery.

 

[Aseras]

The APM is the "alternator" in the ELR or the Volt. I'd expect you to tie directly into the HV DC side. Then as has been said above you can put whatever you want in as long as you match the voltage window.

This is the same idea Leaf people used to scab extra chargers in.

http://www.metricmind.com/leaf/main.htm

 

[aarossig]

Love this forum, thanks for all the great responses!

How many kwhrs will your add on battery pack be?

I haven't decided yet but was hoping to push 10-20kWh. I am planning to use the energy dense (and expensive) LG MJ1 cells in a custom pack (96S8P or 96S12P, something in that range, depends on weight, fuse, etc. etc.). I have also considered Nissan Leaf cells.

A DC-DC allows you to make the 2nd pack any voltage you want.
Two 24 VDC Tesla modules in series would add around 10 kw and almost double your EV range.
This would need to be up converted from 48 VDC to up around 400 VDC with current limiting capabilities.
How do you plan to keep your existing pack safe in terms of possibly over charging it?

Yup, that pretty much describes the setup I have in mind. I have been researching options for DC-DC converters that can achieve my goals and have come up empty handed so far. My ideal setup would be a bidirectional h-bridge buck-boost supply with constant current and constant voltage (CC/CV) modes of operation. If the external battery is 96S, efficiency can also be quite high. Over charging would be handled by the CV phase, just like any other lithium charger.

The really cool feature of it being bi-directional is that the onboard AC charger would also charge the external battery pack

I may have to resort to designing something. I could start with a smaller battery on a bench (say 4S) and work up to 96S. High voltage PCB design requires attention to creepage distance, and it would probably need to be isolated from the 12V bus too (12V to run the embedded system that monitors the two HV packs). The obvious downside here is that I need to spend time on the design and validation. I will keep researching.

A 6 kw transfer rate would of course be 6 kwhr of energy in 1 hour.
If traveling at city speeds 30-50 mph, would mean you could probably get 2/3 of a 10 kwhr pack, less if going highway speeds. Kind of big and heavy, but have you considered a parallel string?

I think for the fact that the parallel string would need to be capable of sourcing high currents (which causes it to be heavy), this option is less-desirable. The transfer rate effectively places a cap on the average speed at which I can travel, which I think is acceptable.

Here's a guy who did that:
http://gm-volt.com/forum/showthread.php?258793-Volt-with-130-140-km-(80-85-mile)-battery-range

This looks like vaporware to me, but who am I?

The BMS is harder to add to the Volt's system. You would add a new BMS (easier to do in hardware) to monitor just the added battery.

I would use a separate BMS. Orion BMS looks popular among DIY EV conversions, but I also found a nice one that can active balance (ie: charge other cells in the pack when balancing) a 96S pack. There is more research to be done here, but I would not tie into the factory BMS.

To answer the question, its a 15amp fuse located in the high voltage battery.

There is nothing else in the circuit but there is a diode on the contactor this circuit is connected to the rest of the high voltage system. The diode may cause this not to work, will not allow currant to flow back in to the battery.

So this is the first reply that could put the brakes on this whole project. Do you have any more info about this diode or service manuals that might contain more details to confirm this?

This is the same idea Leaf people used to scab extra chargers in.

http://www.metricmind.com/leaf/main.htm

I was planning to do exactly this to boost the rate of charge as well. There are some nice Eltek chargers that would work well.

 

[edk-austin]

A diode! Curses! I've thought about this too, given the accessibility of the APM and cable. Or direct DCFC (albeit slow charge) of the battery by solar.

Well, there's still the Sunny Boy string inverter idea for HVDC, vehicle to grid/home application. But limited to about 4KW.

Back to the day job...

 

[aarossig]

Thanks for the replies! This is a great forum.

How many kwhrs will your add on battery pack be?

I had in mind 10-20kWh. I plan to use the energy dense (and expensive) LG MJ1 cells in a custom pack. I have also considered Nissan Leaf modules.

A DC-DC allows you to make the 2nd pack any voltage you want.
Two 24 VDC Tesla modules in series would add around 10 kw and almost double your EV range.
This would need to be up converted from 48 VDC to up around 400 VDC with current limiting capabilities.
How do you plan to keep your existing pack safe in terms of possibly over charging it?

This effectively describes the idea I have in mind. I have been on the lookout for a DC-DC converter that can meet my requirements but have been coming up empty handed. Ideally it would be an h-bridge buck/boost converter with constant current (CC) and constant voltage (CV) modes. The potential for overcharging is mediated by putting the converter in CV mode when the battery reaches peak voltage like any other lithium charger. The pack could be 96S as well which could make the converter quite efficient.

The beauty of this approach is that it could charge the supplemental battery from the onboard AC charger.

Unfortunately (as I'm sure you can imagine) this is a tall order form an off-the-shelf component so I may consider designing something. High voltage PCB layout requires attention to creepage distance and the small embedded system that runs the charger would need to be isolated from the 12VDC bus. The downside of designing my own is well.. I would need to design and validate it. I could start with a 4S pack on a bench and work my way up to a 96S pack.

A 6 kw transfer rate would of course be 6 kwhr of energy in 1 hour.
If traveling at city speeds 30-50 mph, would mean you could probably get 2/3 of a 10 kwhr pack, less if going highway speeds.


Kind of big and heavy, but have you considered a parallel string?

Yup, that's about right. I think the problem with a parallel string is that it needs to be able to source high currents which makes it heavier. I think for this project, the limitation is acceptable.

Here's a guy who did that:
http://gm-volt.com/forum/showthread.php?258793-Volt-with-130-140-km-(80-85-mile)-battery-range

Please post pics of the project!

This looks like vaporware, but who am I?

The BMS is harder to add to the Volt's system. You would add a new BMS (easier to do in hardware) to monitor just the added battery.

I would be using an external BMS. The Orion BMS looks popular among DIY EV conversions, but I also found a 96S active balancing BMS (more efficient). More research here is needed but I wouldn't try to use the onboard BMS.

To answer the question, its a 15amp fuse located in the high voltage battery.

There is nothing else in the circuit but there is a diode on the contactor this circuit is connected to the rest of the high voltage system. The diode may cause this not to work, will not allow currant to flow back in to the battery.

Ah ha, I knew something could put the brakes on this project. Are there any technical references to confirm that the diode is present?

If this is the case, this project might be a non-starter. Are there any other "user accessible" HV points in the vehicle?

 

[Tacoma]

Hey aarossig don't mess with those power cables as you are likely to poke your eye out. Just checking to see if you are there?

Can you provide some specifics on the DC-DC converter you had in mind. Do you have the background and experience to design and build your own?

 

[aarossig]

Hey aarossig don't mess with those power cables as you are likely to poke your eye out. Just checking to see if you are there?

Can you provide some specifics on the DC-DC converter you had in mind. Do you have the background and experience to design and build your own?

Hah! Yes, I am here. I wrote up a nice reply to everyone last night and I guess it didn't get through moderator approval or something. The newcomer restrictions on this forum are quite strict.

I would be looking for a bidirectional DC-DC converter with buck/boost and constant current/constant voltage modes of operation. I did find one last night and sent a request for a quote. I have a background in electronics and embedded systems so I could probably build something but would prefer not to for a variety of reasons.

I pulled the service manual last night and had a look at the APM circuit. I didn't see a diode, though I doubt these system integration level schematics are intended to get to this level. Can anyone confirm the presence of a diode?

 

[Tacoma]

Another thought, even if the DC-DC were smaller yet, say with a 1 to 1.4 kw (like a level 1 charger), this could move power from extra pack to main pack also when not in drive mode. i.e. you drive 40 miles on approximately 10 kwhrs, then when sitting parked perhaps at work, 10 kwhrs transfers over to main pack during 8 hours, and you are good for another 40 miles on the return trip at the end of the day. Super critical to have main pack BMS feedback though, unless there was some way to short charge the main pack safely.

 

[aarossig]

Yup, the need for CC/CV phases would basically ensure that the primary battery is never charged. Standard lithium-ion charging stuff.

The BMS for the external pack is equally important. I was planning to use an off the shelf unit like an Orion BMS, which is popular among DIY EV conversions. I also saw one with active balancing which looked promising.

Still waiting to hear about the cost of the DC-DC converter that I found. Will share more details as they come about.

I am still really bummed that my reply got lost! I spent so much time on it

 

[aarossig]

I am still alive it has been a busy week, so let me share a quick update.

I got current to flow into the car on the HV bus in the trunk, but not much. Only 0.24A at 384V (<100W). This might confirm the diode suggestion, but I think it's time to put the brakes on this project. I used an Enginer DC-DC converter that is ordinarily used for a Prius PHEV conversion. I saw photos of one mounted in a Nissan Leaf so I was intrigued and picked up one on eBay, local LA pickup only. I made a day trip out of it on Saturday. I was up at 5AM with my Tesla charged up to 96% and drove down I-5 making a couple of stops to eat and charge. I arrived home with the batteries, BMS's, DC-DC converters, chargers, etc etc at 11PM after just shy of 800 miles for the day.

After some reversing, I managed to get the DC-DC converter to run (sticking 12V down two undocumented pins engages a relay that enables the output). I found some trimmers inside and managed to tune it work work with the car, albeit in this minimal way.

Frankly, it has been fun to experiment but this project is beyond practical. I will likely move on. I don't trust the DC-DC converter enough to consider mounting it in the car. It is dangerous for the minimal improvement I would get. Thankfully the auction came with a bunch of batteries that are in good condition. Perhaps there is room for a future project here (eBoat? ).

Best to just enjoy the ELR as it was designed Thanks to all those who replied!

 

[ratSnO]

For future searchers ....
The fuse is not "in" the battery pack, it is on the relay assembly (GM Part 22856646 or 24297383 for Gen 1) at the very front of the battery pack and the fuse box in this assembly is accessible from underneath but is not easy to get to, for both Gen 1 and Gen 2 Volts.

For Gen 1, yes, it is a 15 amp fuse. Typically a Bussman Limitron KLM-15 which is fast acting, 600VDC, IR 100 kA. This KLM type fuse is made in higher ratings of 20, 25 and 30 amps 30a.

15 amps is above and below 5000 watts depending on the battery voltage. So well above the 2000 approx watts of the Accessory Power Module (APM)

The Weber Auto YouTube vid on the Gen 2 battery pack gives a great look at the Gen 2 relay assembly which has 4 fuses in it, but he doesn't talk about the APM fuse.