5-6 Volts of sagging

Loginphp

10 mW
Joined
Sep 4, 2021
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I have a 48v parallel battery setup that totals 20ah (10ah each) but I noticed even at full charge I go from 54.7v down to 48/49v at full throttle. What is a healthy amount of voltage sag? Is this unusual? How much voltage sag is too much?

I have not provided details regarding the batteries unless asked because I am just wondering if that amount of sag is normal, period, for any setup.
 
I typically get 2V to 2.2V of sag at full throttle, pulling 35A from 48V batteries that are rated for a lot more than that. The measured sag includes voltage drop across the cables and connectors.

If you're getting 5V sag or more at the battery terminals, you're thrashing your battery way too hard (or it's already thrashed). If much of the total drop is in the cables, you probably have a bad connector burning itself up somewhere.
 
Chalo said:
I typically get 2V to 2.2V of sag at full throttle, pulling 35A from 48V batteries that are rated for a lot more than that. The measured sag includes voltage drop across the cables and connectors.

If you're getting 5V sag or more at the battery terminals, you're thrashing your battery way too hard (or it's already thrashed). If much of the total drop is in the cables, you probably have a bad connector burning itself up somewhere.
Thanks! I figured that. An interesting side note, is that when I connect my batteries after charging them up there used to be a spark or a pop, I heard that was pretty normal, but it never happens now.
 
Loginphp said:
Chalo said:
I typically get 2V to 2.2V of sag at full throttle, pulling 35A from 48V batteries that are rated for a lot more than that. The measured sag includes voltage drop across the cables and connectors.

If you're getting 5V sag or more at the battery terminals, you're thrashing your battery way too hard (or it's already thrashed). If much of the total drop is in the cables, you probably have a bad connector burning itself up somewhere.
Thanks! I figured that. An interesting side note, is that when I connect my batteries after charging them up there used to be a spark or a pop, I heard that was pretty normal, but it never happens now.

Maybe a BMS problem?
 
Loginphp said:
I have a 48v parallel battery setup that totals 20ah (10ah each) but I noticed even at full charge I go from 54.7v down to 48/49v at full throttle. What is a healthy amount of voltage sag? Is this unusual? How much voltage sag is too much?

Depends on what cells your pack is made of, so not unusual if using cheap generic cells. Too much sag would be if your controller LVC cuts power, or when the battery BMS triggers.
 
5-6v is good, 7 or 8 would be too much
The connector may be starting to get destroyed for it to start not popping, or you are plugging the charger into the wall first, before connecting it (as you should)
 
If you have access to borrow a cheap IR camera, you could tide the bike hard for a couple minutes, and then use the camera to see the hotspots.

The bottlenecks to current will run hotter.
 
Update~

First of all, I just wanted to thank everyone here for giving me their knowledgeable input.

Something I recently noticed about the voltage sag.

For example, I noticed when riding for a while and using up some juice, my voltage dropped to 47.7v in a resting state for about 15 min. Ok that's normal, but then I decide to ride again and go full throttle, but then suddenly my sag is literally only about 3v. So if I'm already low on voltage like 47.7 I only sag to 44.7, yet when I have a fully charged battery I sag a whopping 6v. I would go from 54.7 to 48.7.

Does that make sense?

It's like the less battery I have the less the sag becomes. I have no way of knowing if THAT is normal or not. I have my suspicion that it could be due to some bad cells in my batteries because it only sags a lot on a full charge, yet sag drops to 3v after using about half of the juice up.

This really confuses me.
 
The battery internally heating up from the first session

which is causing accelerated wear, vastly reducing longevity

is also vastly reducing internal resistance

thus increasing capacity of power output, thus reducing the V sag resulting from a given current draw.
 
Anything over 53V does not represent much actual energy storage

So don't even count that as voltage sag, even a tiny load would get the pack there very quickly.

There are three ways to reduce your sag issue

1. Reduce the C-rate

1A pull less power

1B expand Ah capacity

2. Buy the top IRL power density cells, revealed through testing and recos by trusted expertz in the forum
 
Nothing you've stated implies outlier bad cells, same symptoms can result from all cells being well matched fresh from the factory

but just being crap cells

or just not designed for high power discharge.

Of course you could have rogue bad cells embedded in your parallel groups.

But no way to tell without testing individual cells after atomising the pack.
 
Before your battery has warmed up, you can get a lot of sag. My controler is ram air cooled in the summer, but in winter its heat is used to warm my battery, This makes quite a differenced to performance and range, with very little voltage drop on cold days.
To cut down voltage drop, I use at least 50 amp batteries, by using high amp cells or many in parallel, good BMS, thick, cables, 8mm by 0.15 pure nickel strips and very ight spotwelds and soldering, including battery cables running lenth of parallel strip.
Most pre built batteries you buy are junk. I was not even impressed when I stripped down a Bosch battery.
Nickel strips and cables very light and the BMS that failed seemed very light weight. Battery cells were good though.
 
ginekolog said:
I have 5.5V sag on 14s5p samsung e35 cells in 30A pull. Quite normal imho. Ma normal ride is 15A with 3V sag.

thats not normal i get under 5v sag with 55A pull and 14S 6P samsung 50g cells
15A with 3V sag is also quite high considering thats only 3A per cell your pulling
 
izy said:
ginekolog said:
I have 5.5V sag on 14s5p samsung e35 cells in 30A pull. Quite normal imho. Ma normal ride is 15A with 3V sag.

thats not normal i get under 5v sag with 55A pull and 14S 6P samsung 50g cells
15A with 3V sag is also quite high considering thats only 3A per cell your pulling
I have a lot to learn about quality batteries and I am going to focus on that more now. What type of batteries do you suggest? You said Samsung cells. Also where would I buy these batteries? I can probably search it on my own if I know the type of batteries I'm looking for. The ones I have are VISET from Amazon but I hear a lot about Samsung cells. My bike would hit 32mph max with me on it, now it barely hits 27/28 with what I THINK is a lot more sag. I vaguely remember the sag before I noticed my performance dropping. I suspect the batteries.

Edit: Is there any requirements off the bat if I were to upgrade my batteries to a higher amp?
 
izy said:
ginekolog said:
I have 5.5V sag on 14s5p samsung e35 cells in 30A pull. Quite normal imho. Ma normal ride is 15A with 3V sag.

thats not normal i get under 5v sag with 55A pull and 14S 6P samsung 50g cells
15A with 3V sag is also quite high considering thats only 3A per cell your pulling

Seems close
14S6P of 50G is 29.4Ah (4.9Ah/cell)
14S5P of 35E is 17.5Ah (3.5Ah/cell)

Pulling 55A from the 50G pack is 1.87C with 5.5V sag
Pulling 30A from the 35E pack is 1.7C with 5V sag

You are pulling a little more relative to pack capacity (10%) and sagging a little more (10%).
 
Most battery packs that I have dismantled, have the entire current traveling through the cables attatched to the positive and negative ends of the battery with a single bloc of solder.
 
E-HP said:
izy said:
ginekolog said:
I have 5.5V sag on 14s5p samsung e35 cells in 30A pull. Quite normal imho. Ma normal ride is 15A with 3V sag.

thats not normal i get under 5v sag with 55A pull and 14S 6P samsung 50g cells
15A with 3V sag is also quite high considering thats only 3A per cell your pulling

Seems close
14S6P of 50G is 29.4Ah (4.9Ah/cell)
14S5P of 35E is 17.5Ah (3.5Ah/cell)

Pulling 55A from the 50G pack is 1.87C with 5.5V sag
Pulling 30A from the 35E pack is 1.7C with 5V sag

You are pulling a little more relative to pack capacity (10%) and sagging a little more (10%).

My pack is 3 years old, 300 cycles and at 86% capacity. Good quality from https://fasterbikes.eu/de/akkus/akkus/225/900wh-flaschenhalter-akku-52v-14s-5p-jumbo-shark?c=159

Sag is this way all the time, I watch it closely as my old pack (Pana PF) sagged 15V -> end of usefull life after 2 years :|
 
Loginphp said:
I have a lot to learn about quality batteries and I am going to focus on that more now. What type of batteries do you suggest? You said Samsung cells. Also where would I buy these batteries? I can probably search it on my own if I know the type of batteries I'm looking for. The ones I have are VISET from Amazon but I hear a lot about Samsung cells. My bike would hit 32mph max with me on it, now it barely hits 27/28 with what I THINK is a lot more sag. I vaguely remember the sag before I noticed my performance dropping. I suspect the batteries.

Edit: Is there any requirements off the bat if I were to upgrade my batteries to a higher amp?

Just guessing, but looking a the description, I'd guess your packs are made with generic Chinese cells, probably 2500mAh capacity. That would be 13S4P for each pack, for $186 each, if this is the correct listing:

https://www.amazon.com/VISET-Warehouse-Electric-Bicycle-Bicycles/dp/B0895J9SNF/ref=sr_1_3?dchild=1&keywords=viset%2B48v%2Blithium%2Bion&qid=1633999081&sr=8-3&th=1

Comparing that with a 13S4P pack using Samsung 35E cells from EM3EV (reputable pack maker based on reading this forum), which are 3500mAh cells, with a 13.6Ah pack capacity (most places would call this a 14Ah pack, 3.5x4, but EM3EV rates their pack conservatively). The EM3EV pack is $429. 36% more capacity, but 2.3 times the cost.

https://em3ev.com/shop/em3ev-48v-13s4p-super-shark-ebike-battery/

Just guessing, but I bet their single 13S5P jumbo pack (17.5Ah, $509) will outperform your paralleled generic packs, at not much more than the cost of your two packs. https://em3ev.com/shop/em3ev-48v-13s5p-jumbo-shark-ebike-battery/
 
E-HP said:
Loginphp said:
I have a lot to learn about quality batteries and I am going to focus on that more now. What type of batteries do you suggest? You said Samsung cells. Also where would I buy these batteries? I can probably search it on my own if I know the type of batteries I'm looking for. The ones I have are VISET from Amazon but I hear a lot about Samsung cells. My bike would hit 32mph max with me on it, now it barely hits 27/28 with what I THINK is a lot more sag. I vaguely remember the sag before I noticed my performance dropping. I suspect the batteries.

Edit: Is there any requirements off the bat if I were to upgrade my batteries to a higher amp?

Just guessing, but looking a the description, I'd guess your packs are made with generic Chinese cells, probably 2500mAh capacity. That would be 13S4P for each pack, for $186 each, if this is the correct listing:

https://www.amazon.com/VISET-Warehouse-Electric-Bicycle-Bicycles/dp/B0895J9SNF/ref=sr_1_3?dchild=1&keywords=viset%2B48v%2Blithium%2Bion&qid=1633999081&sr=8-3&th=1

Comparing that with a 13S4P pack using Samsung 35E cells from EM3EV (reputable pack maker based on reading this forum), which are 3500mAh cells, with a 13.6Ah pack capacity (most places would call this a 14Ah pack, 3.5x4, but EM3EV rates their pack conservatively). The EM3EV pack is $429. 36% more capacity, but 2.3 times the cost.

https://em3ev.com/shop/em3ev-48v-13s4p-super-shark-ebike-battery/

Just guessing, but I bet their single 13S5P jumbo pack (17.5Ah, $509) will outperform your paralleled generic packs, at not much more than the cost of your two packs. https://em3ev.com/shop/em3ev-48v-13s5p-jumbo-shark-ebike-battery/
Spot on with your links. Thanks. I think it's worth the cost to upgrade.
 
Loginphp said:
Spot on with your links. Thanks. I think it's worth the cost to upgrade.

There's nothing wrong with generic cells, as long as you don't treat them like higher performing cells. My first 20Ah pack had generic cells which worked fine for normal riding, but would sag when taxed. I'm still using that pack as backup power for when we have power outages. Good enough to keep our devices charged.

I suggest taking your time to decide exactly what you need for how you ride your bike. The 35E cells are high capacity, but not high current output (8A). Samsung 25R are high output, but lower capacity. In the middle are their 30Q cells, decent capacity and output. Depending on the availability of the cells, EM3EV can build to the spec you want. LG, Sony, and Panasonic/Sanyo have a similar selection of cells. Any of those brands would be considered premium.
 
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