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Old 07-19-2020, 04:21 PM   #1
Left Coast Kiteboarding
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Default Chevy Volt / Navitas AC - New Build

Picked up a sad / abused 2001 DS last week. All I really needed was the the rolling frame and roof assembly as it's gonna get completely rebuilt. Got my California plates on Monday and tile coming in the mail. Plan is to build a street legal cart that will do 25-30 max speed and have 40-60 mi. range. I want to be able to drive it all day from job site to job site without worrying about battery.

There are a bunch of GREAT write-ups on here about similar projects and I've learned a bunch from them all. I'm going a little different direction so figured I'd do a build thread to share.

Initial concept:

Batteries will be from a Chevy Volt. They offer some great advantages. Biggest one being they are available and affordable where I live. I purchased 2 48v 50aH packs with balancing systems for $1600 which is just a little more than a Trojan bank.

The Trojan Ranger has about 170aH rating which translates to around 85 safe useable aH and weighs 390lbs.

The Volt batteries are rated at 47aH each ( 95ah in combination) which safely gives probably 85ah+ useable power. The two banks weigh 45lbs each for total of 90lbs. This shaves 300lbs off the cart from the get go. This translates to very similar power capacity with major weight loss.

In addition, the Volt batteries can deliver a LOT more current if asked. I don't know what the C rating of the Trojans are, but the Volt pack has a continuous discharge rate of 7.5C and a peak rate of 10C meaning that the 85ah pack can continuously supply 700+ amps of current and for short periods deliver 940 amps. This should be plenty for my Navitas 600A controller :-) All this with almost ZERO maintenance.

Add in the conservative 10% efficiency gain and the lower weight of the cart and range should be better...as long as I stay out of the pedal. Long term I plan to double the pack capacity which will still shave 210lbs off the cart and provide almost 200ah of useable power. That's gonna be fun.

For battery management I'm going a hybrid route. Each 48v bank has it's own onboard balancer. IT's not a high current system but while at rest will equalize cells. This happens passively and requires no monitoring.

For charging I have a charger set to cut off voltage at the correct point so that overcharging can not occur. I *may* add an additional cutoff for safety but that remains TBD.

I'm going to use an ECPC404 meter for realtime monitoring. It will monitor realtime amp draw, realtime voltage, and total ah consumption. In addition it has two 'alarm' circuits that can be used to trigger relays. They can be set to trigger on voltage, amps, or ah.

I will use one of these triggers to shut the main power relay off for under-voltage situations. The Navitas has a 'limp' mode that reduces power when the pack gets low so you can still get home and the 404 will provide an absolute cutoff at low voltage either at the end of battery capacity or more importantly during use. If sag voltage gets below a safe level the meter will cut power from the battery. As soon as the voltage comes back up to a set threshold it will turn power back on. I'll set this point at minimum safe pack voltage. It this triggers while driving the cart will stop getting power for a short period of time. The voltage will immediately come up (assuming the pack is not completely discharged.) This will likely happen in a fraction of a second. You will likely still have your foot on the pedal when the power comes back on. Fortunately the Navitas has a feature where it will not power up the motor if the pedal is down when the main power circuit gets charged. What this means is the the meter will cut power. Voltage will rise and power come back on but you will have to release the pedal before the motor will come back online. this will prevent the cart from going into a loop where the relay cycles on and off and rapidly powers and depowers the motor. This would be unpleasant on the passengers and likely really hard on the entire drivetrain.

I'm not sure what to do with the 2nd trigger. I had planned to use it as an over-current safety but given the pack can deliver stupid amounts of power and the Navitas has a knob to dial in power, I may not ever need to use it this way. What I may do is use it to shut the pack down at a minimum SOC. I could tell it to kill the pack after discharging 85ah. IF I do this I'll add a bypass switch somewhere so I can override this function if I'm stuck and need to get home. I'll make this decision once I see how the Navitas system handles this on it's own.

Alternatively, I could use this 2nd relay to add redundancy to my charge system. This is what I'll do if I don't need it for anything else.

I'm aware that I'm ignoring some lever of battery management I could gain from a sophisticated BMS system. There are lots of great products out there that do amazing step. I'm just not convinced I need that level of control. The balancers will generally keep the pack in line and I have overcurent protection (the controller can't out-draw the pack capacity) and under-voltage protection from both the controller and the meter. Over-voltage is handled by only the charger but could be duplicated by the meter. It's entirely possible that with a sophisticated BMS I could get some extension of lifespan but in this application the added cost and complexity seem unnecessary. Given that the battery is rated for over 3000 charge cycles (thats 300 complete charge/discharge cycles, so 2 1/2 discharges only equal one cycle) I could completely discharge and charge almost every day for 10 years. Given that I'll likely rarely use the full capacity this pack should last a very long time. Newer, cheaper options will undoubtedly be available by the time it's done.

Equipment used:

2001 Club Car DS, currently a 48v with MCOR.

Charger:
Schauer JAC1548H programed for the Lithium pack.

Schauer Industrial Chargers

Navitas 600a controller and 5kW motor for the Precedent IQ system
Custom Precedent wiring harness to re-were the DS (From Goft Carts Modified. These guys know the Navitas system very well)

Golf Carts Modified

2 48v 47ah Volt banks. Will ultimately have a total of 4. Sourced locally but available on eBay as well.

ECPC404 Intelligent Ampere Hour Meter from Electric Car Parts Company

Electric Car Parts Company

All 2awg power delivery cables I'll build in-house using high quality welding cable.

Cosmetically the cart will have a 6" lift, new wheels and 22" tires and other cosmetic stuff, but this thread will primarily be powertrain related.

I'll admit I'm not super great at taking photos along the way but I'll try to when appropriate. Looking forward to working through the details as this comes together, and hearing constructive criticism and positive feedback.
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Old 07-21-2020, 07:34 AM   #2
bronsonj
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Default Re: Chevy Volt / Navitas AC - New Build

That looks like a fun project! Do keep in mind that the usable amp hours in a lithium pack are "spread" across a wide range of volts... So if your pack is 12 cells at 4.15vpc you start at 49.8v and if you discharge to 3.25vpc your pack will be dead at 39v.

Have you ever ridden in a 48v lead acid cart when the pack read 39v?.... It's slow... You'll have plenty of speed for the first 3rd of your 12S packs amp hours, but the last 2/3rds... I don't know what the max V of the Navitas controller is, but the Chevy Volt came in 12 cell and 6 cell modules that are factory made to combine with each other. So if the Navitas sells a 72v controller then you can do an 18S pack... Contact Navitas and see what the max V your controller can handle.

I have a 14S2P Chevy Volt Pack for 94ah at 57.6v max. To get a 14S you have to get creative the cell connections. But with my small 300 amp controller I can do wheelies when I turn it all the way up! Removing 300+ pounds does make a huge difference! I have 22" tires and a lift as well, my EZGO is certainly going to ride differently than your DS, but I can tell you 30mph is the point where it becomes no fun anymore...

Cool build and good luck!
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Old 07-21-2020, 08:01 AM   #3
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by bronsonj View Post
That looks like a fun project! Do keep in mind that the usable amp hours in a lithium pack are "spread" across a wide range of volts... So if your pack is 12 cells at 4.15vpc you start at 49.8v and if you discharge to 3.25vpc your pack will be dead at 39v.

Have you ever ridden in a 48v lead acid cart when the pack read 39v?.... It's slow... You'll have plenty of speed for the first 3rd of your 12S packs amp hours, but the last 2/3rds... I don't know what the max V of the Navitas controller is, but the Chevy Volt came in 12 cell and 6 cell modules that are factory made to combine with each other. So if the Navitas sells a 72v controller then you can do an 18S pack... Contact Navitas and see what the max V your controller can handle.

I have a 14S2P Chevy Volt Pack for 94ah at 57.6v max. To get a 14S you have to get creative the cell connections. But with my small 300 amp controller I can do wheelies when I turn it all the way up! Removing 300+ pounds does make a huge difference! I have 22" tires and a lift as well, my EZGO is certainly going to ride differently than your DS, but I can tell you 30mph is the point where it becomes no fun anymore...

Cool build and good luck!
Navitas TAC2 AC controller works with 72v nominal packs (actual voltage up to around 85 or so I think, but check specs).

"Limp" mode likely won't work properly with lithium packs (new FW is partially done allowing more control over battery type though) because the voltage discharge curves and points are different for LiOn -vs- FLA and the Limp mode in legacy FW is set for FLA. I have a Tac2, 5KW motor so know this to be accurate. The newer, forthcoming FW will allow for setting more parameters for regen as well as limp mode trigger conditions.
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Old 07-21-2020, 04:55 PM   #4
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Default Re: Chevy Volt / Navitas AC - New Build

Quote:
Originally Posted by bronsonj View Post
That looks like a fun project! Do keep in mind that the usable amp hours in a lithium pack are "spread" across a wide range of volts... So if your pack is 12 cells at 4.15vpc you start at 49.8v and if you discharge to 3.25vpc your pack will be dead at 39v.

Have you ever ridden in a 48v lead acid cart when the pack read 39v?.... It's slow... You'll have plenty of speed for the first 3rd of your 12S packs amp hours, but the last 2/3rds... I don't know what the max V of the Navitas controller is, but the Chevy Volt came in 12 cell and 6 cell modules that are factory made to combine with each other. So if the Navitas sells a 72v controller then you can do an 18S pack... Contact Navitas and see what the max V your controller can handle.

I have a 14S2P Chevy Volt Pack for 94ah at 57.6v max. To get a 14S you have to get creative the cell connections. But with my small 300 amp controller I can do wheelies when I turn it all the way up! Removing 300+ pounds does make a huge difference! I have 22" tires and a lift as well, my EZGO is certainly going to ride differently than your DS, but I can tell you 30mph is the point where it becomes no fun anymore...

Cool build and good luck!
quick question. I have 3 48v chevy volts that I have with an alltrax sr48400. Is your ezgo not a series. Mine doesnt pop wheelies. There is plenty of torque but not enough to bringthe wheels of the ground.
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Old 07-21-2020, 09:00 PM   #5
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by kofifi View Post
quick question. I have 3 48v chevy volts that I have with an alltrax sr48400. Is your ezgo not a series. Mine doesnt pop wheelies. There is plenty of torque but not enough to bringthe wheels of the ground.
My cart is a sepex cart and I love the regen that sepex offers.

I created the battery pack to be a 14S2P pack so it's 94 amp hours and 57.6v. I have a 3 mode personality switch so I had base mode, normal mode and crazy mode programmed in. The crazy mode was too much (yes, even with only a 300 amp Alltrax). I was pulling wheelies from a dead stop with nobody else in the cart other than myself. I didn't have someone on the back seat or anything as such.

I have since turned down the acceleration rate to prevent wheelies because that cannot be easy on the cart as the driver's side wheel is much lower than the passenger side since there's no weight over there. Now, I basically leave the cart in 'normal' mode. I've reprogrammed the crazy mode to be a little slower accel and a little slower top speed so it reaches 27/28mph in crazy, 24 in 'normal' and 20 in base mode.

Honestly, I bought the cart with the lift and the tires already on it. I only added the Chevy Volt cells and the Alltrax 300 amp. Everything else I have done has been cosmetic or to accessorize or other small changes that are not for performance. Stock gears, stock motor still in it.

But three 12S packs in parallel give you 49.8v and 141 amp hours. When I was on the stock controller still (it worked fine on 57.6v for the 3 or 4 weeks I ran it that way), I noticed a big improvement in performance when the voltage was higher than the 50.7 that a fully charged lead acid pack would provide. Now that I have the Alltrax, it is still obvious that fully charged down to maybe 53v is max performance.
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Old 07-21-2020, 09:10 PM   #6
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by fstop View Post
Navitas TAC2 AC controller works with 72v nominal packs (actual voltage up to around 85 or so I think, but check specs).
So that's exciting because from what I've seen the performance more-or-less scales up with voltage.

If I were starting over and had the controller that could handle the voltage, I'd go with a 18S Chevy Volt pack for 74.17v max. That'd make for a lively cart!
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Old 07-25-2020, 12:24 AM   #7
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by fstop View Post
Navitas TAC2 AC controller works with 72v nominal packs (actual voltage up to around 85 or so I think, but check specs).
Per Navitas, the new controller will handle 100v.

Quote:
"Limp" mode likely won't work properly with lithium packs (new FW is partially done allowing more control over battery type though) because the voltage discharge curves and points are different for LiOn -vs- FLA and the Limp mode in legacy FW is set for FLA. I have a Tac2, 5KW motor so know this to be accurate. The newer, forthcoming FW will allow for setting more parameters for regen as well as limp mode trigger conditions.
If the onboard limp wont work I'll simply set the shut down voltage in my management system to cut off early and then just put in an override switch to let me get home. I'll be reaching out to Navitas again once its installed to talk programing details.
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Old 07-25-2020, 12:31 AM   #8
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Default Re: Chevy Volt / Navitas AC - New Build

Quote:
Originally Posted by bronsonj View Post
That looks like a fun project! Do keep in mind that the usable amp hours in a lithium pack are "spread" across a wide range of volts... So if your pack is 12 cells at 4.15vpc you start at 49.8v and if you discharge to 3.25vpc your pack will be dead at 39v.
Can you explain this more? The voltage curve for Li packs are pretty flat...meaning voltage drops off slowly over the use cycle. I'm unclear on what you mean aH are spread across voltages?

Quote:
Have you ever ridden in a 48v lead acid cart when the pack read 39v?.... It's slow... You'll have plenty of speed for the first 3rd of your 12S packs amp hours, but the last 2/3rds...
If I'm not mistaken, voltage in a Li pack should fade slower than Lead, no? If voltage equates to speed why would a Li pack not maintain speed over a longer period of time....assuming I were to keep my foot out of the pedal and not just burn up capacity?
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Old 07-25-2020, 12:34 AM   #9
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Default Re: Chevy Volt / Navitas AC - New Build

Got the lift and wheels/tires on today. The tired old Lead pack only goes about 1 mile. Can't wait to get going on the drive system next week. Parts are all here.
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Old 07-25-2020, 08:10 AM   #10
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by Left Coast Kiteboarding View Post
Per Navitas, the new controller will handle 100v.



If the onboard limp wont work I'll simply set the shut down voltage in my management system to cut off early and then just put in an override switch to let me get home. I'll be reaching out to Navitas again once its installed to talk programing details.
To be clear, the limp mode will work soon with lithium - it's just that at the moment, it is set for 48v FLA and the voltage never gets that low under load on a lithium pack that is 51v or more, so it never engages. If you ask them about this directly please report back to the group if you can.

When you say "new" controller - are you saying there is a newer version of the tac2 where the upper voltage limit differs from older ones? Or have they always been capable of 100v max?
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