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Old 07-25-2020, 08:23 AM   #11
fstop
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by Left Coast Kiteboarding View Post

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?
I'll let him respond to you also with his take, but my experience is that FLA fades pretty quick, and the fade is very evident. It gets really bad with the Navitas setup if you are using some accel and or speed. I hit "limp" mode any number of times w/out putting many miles on a fully charged FLA pack - especially when I had a few others in the cart.

My RoyPow, on the other hand, has essentially no detectable fade (flat voltage curve through most of the pack's capacity). To be fair, I've only run it down below 30% once or twice, when range testing, and I didn't push it too hard with acceleration or WOT runs when in this SOC, but the range on this pack is so much greater than my FLA pack that by the time I hit 30% SOC I've likely already traveled 30-35 miles. Generally my longest trips between charging are no more than 20 miles max with 10-12 being the norm, and being able to charge at about 10mph means short charge sessions are productive.
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Old 07-25-2020, 12:00 PM   #12
Left Coast Kiteboarding
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by fstop View Post
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.
I will report back!

Quote:
When you say "new" controller - are you saying there is a newer version of the tac2 where the upper voltage limit differs from older ones?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?
I cant answer that. I was told that the one I was receiving would handle 100v. Can't speak to older models. I will confirm this again when I talk to them.
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Old 07-25-2020, 12:03 PM   #13
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Default Re: Chevy Volt / Navitas AC - New Build

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I'll let him respond to you also with his take, but my experience is that FLA fades pretty quick, and the fade is very evident. It gets really bad with the Navitas setup if you are using some accel and or speed. I hit "limp" mode any number of times w/out putting many miles on a fully charged FLA pack - especially when I had a few others in the cart.

My RoyPow, on the other hand, has essentially no detectable fade (flat voltage curve through most of the pack's capacity). To be fair, I've only run it down below 30% once or twice, when range testing, and I didn't push it too hard with acceleration or WOT runs when in this SOC, but the range on this pack is so much greater than my FLA pack that by the time I hit 30% SOC I've likely already traveled 30-35 miles. Generally my longest trips between charging are no more than 20 miles max with 10-12 being the norm, and being able to charge at about 10mph means short charge sessions are productive.
THAT is all I want. Yes, silly speed is always fun but really all I want is an all day cart. Your experience with the Li pack mirrors my expectations based on the discharge curves. REALLY looking forward to dumping 400 lbs of lead!!
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Old 07-25-2020, 12:58 PM   #14
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Default Re: Chevy Volt / Navitas AC - New Build

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Originally Posted by Left Coast Kiteboarding View Post
THAT is all I want. Yes, silly speed is always fun but really all I want is an all day cart. Your experience with the Li pack mirrors my expectations based on the discharge curves. REALLY looking forward to dumping 400 lbs of lead!!
You'll be happy, I think.

One thing to think about (that I didn't think about) is that the ride becomes a lot more stiff when losing all that weight. I ended up removing the front helper leaf on my lifted Onward, and running fairly low air pressure. It was never an issue on a smooth street, but even expansion joints on paved paths or roots on the golf course were jarring. Considerably better now, but still not quite what it was before.
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Old 07-25-2020, 01:36 PM   #15
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Default Re: Chevy Volt / Navitas AC - New Build

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You'll be happy, I think.

One thing to think about (that I didn't think about) is that the ride becomes a lot more stiff when losing all that weight. I ended up removing the front helper leaf on my lifted Onward, and running fairly low air pressure. It was never an issue on a smooth street, but even expansion joints on paved paths or roots on the golf course were jarring. Considerably better now, but still not quite what it was before.
For sure. I've been pulling the extra leaf out of the front for years. Right now the rear factory springs twist so much that the ride is unacceptable. Rather than add stiffer leafs to fix the twist...and harsh out the ride even more...I'm going to fab up a 4 link rear end with come coil-over shocks.
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Old 07-25-2020, 03:25 PM   #16
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Default Re: Chevy Volt / Navitas AC - New Build

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For sure. I've been pulling the extra leaf out of the front for years. Right now the rear factory springs twist so much that the ride is unacceptable. Rather than add stiffer leafs to fix the twist...and harsh out the ride even more...I'm going to fab up a 4 link rear end with come coil-over shocks.
That'll be nice. Above my pay grade!
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Old 07-27-2020, 04:01 PM   #17
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Default Re: Chevy Volt / Navitas AC - New Build

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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?
I'd say the discharge is linear and not flat. So in my Chevy Volt pack (just like the Nissal Leaf packs) the max charge is 4.15v per cell. Some people go up to 4.17 but the norm is 4.15 and my personal max is 4.11vpc. The max discharge is something above 3.00vpc. I have my max discharge at 3.25vpc.

So if you have 12 cells in series, you will start at 49.8V and need to recharge at 39v. In contrast a lead acid pack starts at 50.7V and needs to recharge at 48V. So the lithium cells span a 10V range from full to dead whereas the lead acid spans 2.7V. The lithium is much more linear (until it gets to the 'knee'). The benefit of the lithium is that you are not limited to 12 cells. If you put 13 cells in series you have 53.95V charged to 42.25V discharged. If you go with 14 cells you have 58.1V to 45.5V. I have 14 cells and choose to only charge my pack to 57.6V (4.11vpc) to increase the life of the pack.

Also, lithium has lower internal resistance so when you mash the pedal the voltage will sag, but much less than lead acid. This means you will accelerate faster. Also lithium weighs a lot less, so you accelerate faster. If I were to recommend a person who is starting from scratch, I'd recommend going with a higher voltage pack if your controller can handle it. Supposedly the Navitas will handle 100V so it will handle a lot more cells than you have. a 20S pack won't be an issue for that Navitas.

The last thing I want to say is that you are switching to AC. AC carts behave a lot differently than DC carts. My cart is a DC cart. So you may see no issues from a 49V pack vs a 57V pack.
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Old 07-29-2020, 04:38 PM   #18
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Default Re: Chevy Volt / Navitas AC - New Build

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I'd say the discharge is linear and not flat. So in my Chevy Volt pack (just like the Nissal Leaf packs) the max charge is 4.15v per cell. Some people go up to 4.17 but the norm is 4.15 and my personal max is 4.11vpc. The max discharge is something above 3.00vpc. I have my max discharge at 3.25vpc.

So if you have 12 cells in series, you will start at 49.8V and need to recharge at 39v. In contrast a lead acid pack starts at 50.7V and needs to recharge at 48V. So the lithium cells span a 10V range from full to dead whereas the lead acid spans 2.7V. The lithium is much more linear (until it gets to the 'knee'). The benefit of the lithium is that you are not limited to 12 cells. If you put 13 cells in series you have 53.95V charged to 42.25V discharged. If you go with 14 cells you have 58.1V to 45.5V. I have 14 cells and choose to only charge my pack to 57.6V (4.11vpc) to increase the life of the pack.

Also, lithium has lower internal resistance so when you mash the pedal the voltage will sag, but much less than lead acid. This means you will accelerate faster. Also lithium weighs a lot less, so you accelerate faster. If I were to recommend a person who is starting from scratch, I'd recommend going with a higher voltage pack if your controller can handle it. Supposedly the Navitas will handle 100V so it will handle a lot more cells than you have. a 20S pack won't be an issue for that Navitas.

The last thing I want to say is that you are switching to AC. AC carts behave a lot differently than DC carts. My cart is a DC cart. So you may see no issues from a 49V pack vs a 57V pack.
Got it. I understand what you mean. True, the min. v for lithium is lower than the min. v for lead. However if you look at the curve the Li holds close to full voltage for about 75-80% of it's capacity. I suspect with the AC I'll be fine. If not I can always buy another 48v pack, split it in half and add to my current 48v packs, giving me a two 50aH 72v packs....that wouldn't suck!
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Old 07-29-2020, 08:27 PM   #19
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Default Re: Chevy Volt / Navitas AC - New Build

Got my CA plates last week. Title came in the mail today. :-)

Got the 5kw Navitas motor mounted up today. It fit...BARELY. There were a few challenges. The jakes top spring plate that has the shock mount barely clears the lower corner of the motor. The factory shock is no lonnger viable as is. I flipped it over but the housing still rubs on one of the electrical connectors on the motor case.

I'll either make a new upper spring plate that moves the lower shock mount rearward, or just completely change up the shock situation with the new rear suspension I fab up.

Not sure if I'm gonna do a 4 link or just radius arms and a panhard rod. After getting the motor in and seeing how things sit I'll probably do a 4 link as it will be easir in the end. I have 20ft of 1" .065 wall tubing waiting for me at the metal supply along with a sheet of .063 aluminium sheet. The tubing is for the suspension. Sheet is to enclose the battery compartment.

It's gonna be REAL hard to not jusr rush to get it running. I want soo badly to see how it runs, but I'm gonna take my time and put it together nice and clean.
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Old 07-30-2020, 07:05 AM   #20
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Default Re: Chevy Volt / Navitas AC - New Build

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It fit...BARELY...

It's gonna be REAL hard to not jusr rush to get it running. I want soo badly to see how it runs, but I'm gonna take my time and put it together nice and clean.
HA!

I hear 'ya on both counts!

I put my motor in by myself, from underneath, with the (lifted) cart not jacked up. Somewhat challenging - the thing's a beast.
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