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Caring for LiHV is a bit different than standard LiPo

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Caring for LiHV is a bit different than standard LiPo

Old 01-13-2021, 03:30 PM
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Exclamation Caring for LiHV is a bit different than standard LiPo

Im sure you have all seen the trend in racing, LiPo is being killed off at most tracks in exchange for LiHV, for that oh-so sweet extra 0.15V Per cell (4.35V per cell max charge LiHV VS 4.20V per cell max charge LiPo). Its no secret that more voltage equals more power and speed, and that is why we buy bigger batteries for the bigger and faster RCs in our lives. But what makes these LiHV batteries different? Do I need to treat them differently? Well as someone who go into LiHV about a year ago and has done extensive research and testing to see just how different they are, I now have enough information to let you guys know what is up with this newer battery technology.

So, what is LiHV? Well, in reality the basic chemical and materials makeup is no different than a standard LiPo, although most LiHV options tend to be "Graphene" models with a very small mount of the element infused into the cell construction to boost performance. However, Graphene models are also available in standard 4.20V LiPo packs, so this is in fact not a difference, its just that LiHV models are made for racing and so they tend to be higher-end, more expensive batteries with more features.

So what is different about LiHV then? Well, to be honest, NOTHING. See in reality, most standard LiPo cells can take 4.35V without exploding, but it will degrade the lifespan of the cells rather quickly and there is a BIG chance of an explosion when overcharging a standard LiPo and you should NEVER try this. So wait then, how do LiHV deal with the extra voltage? Why is it safe on LiHV and not standard LiPo? Well simply put, its the quality of the cells put into the packs. The cells that get chosen to go into LiHV packs are ONLY the absolute best, most resilient, and most powerful cells a manufacturer has to offer, which is why the packs are so expensive. There is simply NO WAY to make a LiHV pack cheaper than a standard LiPo with the same number of cells and capacity. These LiHV cells are also tested before being sold, with batch samples undergoing hundreds of cycles to full 4.35V and then being completely discharged before being deemed safe to sell and label as a LiHV pack.

So how do I care for these LiHV packs? Nearly the same way you care for standard LiPos with one exception. Some of you may remember that I did an experiment a while back and posted my surprising results to the RCTech forums. This experiment showed that dropping voltage to absolute minimum 3.0V per cell actually slowly damages a LiPo pack over time, and that most LiPo packs will actually hit their rated capacity going from full charge 4.20V per cell down to about 3.3-3.4V per cell. These tests were performed on new batteries, all of which had either never been cycled or had been cycled less than 20 times. Batteries are a CONSUMABLE item and do not last forever no matter what you do and will loose capacity and performance as they degrade over time, its simply an unfortunate fact that cannot be avoided. This showed why those who set their LVCs on their ESCs to minimum 3.0 per cell were having so many LiPo issues for so long. Well, with LiHV unfortunately the news gets a bit worse. Some manufacturers will even label LiHV packs to say "DO NOT DISCHARGE BELOW 3.3V PER CELL!!!" Well this label DOES exist for a real reason. As with LiPo, manufacturer instructions have once again mis-lead us.

With testing, I was able to determine that MOST LiHV packs hit their capacity rating when being discharged slowly at under 0.5C discharge rate from full 4.35V per cell to roughly 3.40-3.50V per cell. Now luckily the "bottom of the fuel tank" is only slightly higher than the standard LiPo so I have been running with my same 3.4V per cell cutoff as I always have, despite running LiHV batteries. Its such a small difference that the LiHV packs should not suffer degradation, especially considering that when on throttle, your pack voltage sags and so when LVC occurs, voltage usually bounces back up to 3.5+V per cell by the time I stick the pack back on the charger.

As for Storage Voltage, 3.80-3.85V per cell is still perfectly safe for both LiHV and LiPo, so do not worry about making any changes here.

One last thing, lets talk longevity. Because LiHV packs are just over-charged, very high-end standard LiPo cells, I imagine you are concerned about the lifespan of LiHV in general. Well, there is a bit of reason for concern, but you can compensate, let me explain. Lithium-Based batteries do not enjoy voltage change in general. Despite the fact that the entire reason for their existence is to be a BATTERY whose sole purpose is to be charged and discharged, all Lithium cells degrade when charged or discharged, PERIOD. The amount of degradation depends on a number of factors including how hot you get your battery, how fast you set your charge speeds, and our topic today will be how far you charge and discharge your batteries. You can look up hundreds of articles that will tell you that LiHV does not last anywhere near as long as standard LiPo, so lets see if we can alleviate some of that degradation...

You see, if you did very tiny cycles to your LiPos or LiHVs, like charging to just 4.1V per cell and discharging to just 3.8V per cell, your Lithium batteries would actually last thousands and thousands of cycles before needing to be replaced. However, this would make for extremely short run times, so short that most would find it unacceptable. The average 5000mAh bash LiPo would become a puny 2000 or even less mAH pack. So, what is a good balance? What is the ideal voltage start and ending for a cycle? Well, since standard 4.20V cells are much cheaper, just go ahead and charge those to standard full charge and try to set your LVCs to 3.4V per cell. A standard, slow-ish charge rate of 0.5-1.5C will ensure maximum lifespan, and of course don't mistreat them. This practice should yield a LiPo that lasts for about 500-600 cycles, or roughly 4-5 years for the average basher who runs once per week with 2 packs and 2 cycles per pack that he/she alternates between so they don't have to drag a charger to a bash spot or can charge one pack while running the other. LiPos and LiHV do have shelf life limits. After a few years sitting around any LiPo or LiHV will degrade badly so the best way to get the most bang for your buck is to make sure you buy batteries you will actually use regularly.

As for LiHV, because they are overcharged cells, the less you push past 4.20V per cell, the longer they will last. I personally charge my LiHV packs to exactly 4.31V per cell. Why such an odd number? Well any battery regardless of chemistry will drop a slight bit in voltage when unplugged from the charger because the act of "shoving amperage" into a battery has the same effect of a motor causing voltage sag, only in the opposite direction. My goal is to be as close to 4.30V per cell as possible when my vehicle starts up. This still gives me a noticeable advantage over competition running standard LiPos but prevents some of the degradation caused by the over-charging. Unfortunately I have not used LiHV long enough to have fully degraded a battery to be sure about this, but performance is still above a brand new standard LiPo after a year and so I believe this is a good sign so far. Just as with standard LiPo, do not abuse or over-discharge the pack.

I hope I was able to help some of you guys considering the LiHV route. Not all tracks conform to strict IFMAR and ROAR rules so there are plenty of ways to see the advantage on a track. Get out there and have fun with RC!

Last edited by wallacengineeri; 01-13-2021 at 04:11 PM.
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Old 01-13-2021, 04:57 PM
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Interesting.

From your perspective, would buying a Li
VH, but only charging to 4.2 be cost effective in that the pack would have less abuse and last longer therefore offsetting the cost difference between LiPo and LiHV?
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Old 01-13-2021, 05:01 PM
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Originally Posted by Silverbullet555 View Post
Interesting.

From your perspective, would buying a Li
VH, but only charging to 4.2 be cost effective in that the pack would have less abuse and last longer therefore offsetting the cost difference between LiPo and LiHV?
No, I charge LiHV to 4.30VPC, its still a decent boost over standard LiPo without pushing it to the ragged edge and degrading too fast. Whether LiPo or LiHV, charging past 4.20VPC exponentially speeds up degradation. So I charge LiHV to 0.05V less than max to slow the degradation a bit while maintaining a performance advantage over standard LiPo.
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Old 01-13-2021, 05:12 PM
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Originally Posted by wallacengineeri View Post
No, I charge LiHV to 4.30VPC, its still a decent boost over standard LiPo without pushing it to the ragged edge and degrading too fast. Whether LiPo or LiHV, charging past 4.20VPC exponentially speeds up degradation. So I charge LiHV to 0.05V less than max to slow the degradation a bit while maintaining a performance advantage over standard LiPo.
But, if you don't need that performance advantage. Would a LIHV charged to 4.2 degrade slower than a LiPo charged to 4.2? And, would the difference between degradation rates be cost effective?
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Old 01-13-2021, 05:18 PM
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Originally Posted by Silverbullet555 View Post
But, if you don't need that performance advantage. Would a LIHV charged to 4.2 degrade slower than a LiPo charged to 4.2? And, would the difference between degradation rates be cost effective?
No. We're only allowed to charge to 4.2V as per our racing rules, and the guys with LiHV batteries are not getting any more life out of their packs than anyone else.
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Old 01-13-2021, 05:24 PM
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Originally Posted by Silverbullet555 View Post
But, if you don't need that performance advantage. Would a LIHV charged to 4.2 degrade slower than a LiPo charged to 4.2? And, would the difference between degradation rates be cost effective?
I couldn't be absolutely sure of that. I haven't seen anyone test that and neither have I. I am sure that because they use such high-end cells that yes they would indeed degrade slower than standard LiPos by a noticeable degree. However, the cost of a LiHV is so high that I seriously doubt it would ever be more cost effective. Setting your LVC higher on a standard LiPo is enough to slow its degradation to a noticeable degree as well.

Might I suggest SMC Racing Extreme Graphene V2 if you want a very high performance, long lasting pack that is not LiHV. Great value too. 4S 6000mAH LCG race-focused pack goes for just $80 USD. The biggest issue with only running a LiHV to 4.20VPC would be that you would loose a lot of capacity. A 6000mAH 4S LiHV pack charged to only 4.20VPC would only have a little over 5000mAH capacity to use and the rest is useless weight, and a typical LiHV 4S pack near 6000mAH costs over $120 USD, a full 50% more expensive.

You are far better off just getting the pack that is right for your use case.
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Old 01-13-2021, 05:46 PM
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Recently, my back yard series has added a provision for use of LiPo HV. My track runs four 17.5 ST's and two 21.5 ST's. Rules provision allows for HV use in the 21.5's, but not in the 17.5's. Thinking that might add a bit of performance to the 21.5's and even the series more. Still waiting on extended term overall results to shake out to see if there is any advantage to the 7.6HV over the conventional 7.4.

Did notice the 7.6V HV I am buying come in lighter and slightly dimensionally smaller than the 7.4V counterpart. Whether this plays into overall performance is yet to be determined. It is, at least a planning factor to consider for the serious racer competing in a series open to HV.

Regarding caring for the HV: My charger has an HV provision for charge and storage separate from conventional 7.4V LiPo. Beyond that, treat and store them the same as LiPo 7.4's. Spec pack for my series is 2s x 4600.

Cheers. 'AC'
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Old 01-13-2021, 06:20 PM
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Originally Posted by wallacengineeri View Post
However, the cost of a LiHV is so high that I seriously doubt it would ever be more cost effective. Setting your LVC higher on a standard LiPo is enough to slow its degradation to a noticeable degree as well.
LiPo and LiHV packs are the same price wherever I look (assuming you're comparing equivalent "race grade" packs).

Originally Posted by wallacengineeri View Post
Might I suggest SMC Racing Extreme Graphene V2 if you want a very high performance, long lasting pack that is not LiHV.
SMC have come out and stated that these "graphene" packs are equivalent to LiHV. I've done my own tests with my LiHV and LiPo packs and also found there's no advantage to LiHV discharge curves.
https://www.smc-racing.com/Regular%20vs%20LiHV
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Old 01-13-2021, 06:22 PM
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Originally Posted by AHR43 View Post
Did notice the 7.6V HV I am buying come in lighter and slightly dimensionally smaller than the 7.4V counterpart. Whether this plays into overall performance is yet to be determined. It is, at least a planning factor to consider for the serious racer competing in a series open to HV.
If the HV pack is rated at the same capacity as the 7.4 pack, it should be lighter, since it's actually lower capacity when charged to the same level (4.2V per cell).
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Old 01-13-2021, 06:23 PM
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Originally Posted by AHR43 View Post
Did notice the 7.6V HV I am buying come in lighter and slightly dimensionally smaller than the 7.4V counterpart. Whether this plays into overall performance is yet to be determined. It is, at least a planning factor to consider for the serious racer competing in a series open to HV.
Exactly, what you are seeing is that the LiHV packs are just in fact overcharged standard cells. Lets imagine a standard 4.20VPC 2S 4000mAH pack. This pack instantly transforms into a 4.35VPC LiHV 2S 4500-ish-mAH pack when overcharged to LiHV voltage. Same exact LiPo with same exact dimensions. The only difference is the cells in the LiHV version are high enough quality to be overcharged without catastrophic failure. The end, thats how LiHV is made. In order to gain capacity WITHOUT changing a given voltage, a battery MUST grow in size physically.

Basically what has happened is because LiPo has been around for about 2 decades at this point, the technology has progressed to where the highest quality cells can be SAFELY subjected to overcharging, its really that simple. The only difference between now and a few years ago is that the cells weren't as strong and so even though you could have invented LiHV yourself by simply overcharging your standard LiPo, it would more than likely result in catastrophic failure and an explosion of fire. So really, any one of us could have been the founding father of LiHV. Ironic, isn't it?
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Old 01-13-2021, 06:50 PM
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You know what though, despite the fact that LiPo "C" Ratings are completely made up and despite the fact that LiHV is kind of just a lie, sort of???... Regardless we should all be happy that LiPo technology has progressed this far. Because what this means is more power and more capacity in a smaller package, and that means a higher power-to-weight ratio.

We all know what a higher power-to-weight ratio gets you - More speed.

I can't wait for the day that LiHV overcharged cells can last just as long as a standard LiPo. That will be a significant game changer for everyone, bashers, crawlers, racers, it doesn't matter at that point. You can always just let off the throttle to go slower when you need to, so who wouldn't buy LiHV when it becomes so good and less expensive that there really is no benefit to choosing older 4.20VPC technology?
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Old 01-13-2021, 07:26 PM
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Originally Posted by wallacengineeri View Post

Basically what has happened is because LiPo has been around for about 2 decades at this point, the technology has progressed to where the highest quality cells can be SAFELY subjected to overcharging, its really that simple.
Not completely unlike the "pushed" cells we ran back in the late80's and early 90's.

Originally Posted by wallacengineeri View Post
You know what though, despite the fact that LiPo "C" Ratings are completely made up and despite the fact that LiHV is kind of just a lie, sort of???... Regardless we should all be happy that LiPo technology has progressed this far. Because what this means is more power and more capacity in a smaller package, and that means a higher power-to-weight ratio.

We all know what a higher power-to-weight ratio gets you - More speed.
I do kind of laugh when people complain about the cost these days. We used to pay $60-80 per pack and could only use them once per week and we got less than a season out of them. If you were going to 3-4 big races per year, you were spending $1000+ on batteries to have a couple new ones at each race.
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Old 01-13-2021, 07:30 PM
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Originally Posted by Silverbullet555 View Post
Not completely unlike the "pushed" cells we ran back in the late80's and early 90's.
I do kind of laugh when people complain about the cost these days. We used to pay $60-80 per pack and could only use them once per week and we got less than a season out of them. If you were going to 3-4 big races per year, you were spending $1000+ on batteries to have a couple new ones at each race.
Ya see I couldn't spend a freaking grand on just batts in a year, thats where I would just say "screw this hobby" and Im sure most people would feel the same at that point. Thats some extreme dedication, and thats coming from the guy with a $2000 Kraton EXB as his avatar lolololol
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Old 01-13-2021, 07:37 PM
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Originally Posted by wallacengineeri View Post
Ya see I couldn't spend a freaking grand on just batts in a year, thats where I would just say "screw this hobby" and Im sure most people would feel the same at that point. Thats some extreme dedication, and thats coming from the guy with a $2000 Kraton EXB as his avatar lolololol
LOL. That was just batteries. We ran cap tires at $50 per set and needed at least 2 sets per class for a big race. Motors were $50ish with sponsor discounts and we were cutting coms every run so they didn't last. Nevermind about all the other parts and consumables! These are 1988-1990 dollars to. Adjust that crap for inflation.
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Old 01-13-2021, 07:43 PM
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Originally Posted by Silverbullet555 View Post
LOL. That was just batteries. We ran cap tires at $50 per set and needed at least 2 sets for a big race. Motors were $50ish with sponsor discounts and we were cutting coms every run so they didn't last. Nevermind about all the other parts and consumables! These are 1988-1990 dollars to. Adjust that crap for inflation.
Ya, just no, hell no lol
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