Discharge Protection for High Cap Tenergy 2600mAh AA

Batteries and Chargers Rechargeable Batteries
8

Found something interesting……

Take a look……

NE555 Low Voltage Battery Disconnect Circuit
Low Voltage Cut Off

9

If the number of cells is at least 3, you can use a li-ion BMS (leave alone the 1 or 2 remainder cells if not exact multiple of 3, they'll be fine). It may limit a bit the charging voltage, but this is probably no big deal. Certain protection chips allow higher charging voltages, though it is unlikely for a stock BMS to come pre-configured for any higher than 4.2V per stage.

See this also: Balancing Ni-MH Battery Packs @ Electro Schematics

Cheers ^:)

10

Thanks.

This particular Vacuum uses 2 AA’s. Dog gone it.

11

Here’s a SImple Low Battery Warning Curcuit. Unfortunately it doesn’t have a cut off……but instead lights a LED if the voltage drops too low.

Low battery warning

12

Practically flat is not an issue with NiMh. You can run single cells dead and not do much damage if any. The problem arises when you run a series too hard, one cell goes dead, and you continue to draw current from the ‘pack’. This can cause reverse polarity in the zero-volt cell and can effectively ruin it. I have seen this in multi-cell packs. I have not seen this problem in simple pairs like you are going to use. My experience is one cell dies, you ‘boot’ it in a dumb charger a couple minutes > throw it in a decent charger, and let it charge back up.

IMO, you are over thinking the issue. Doubt the vacuum will run worth a damn on depleted cells if it is a high draw application. Not sure how well those particular cells will work in actual use. Unfortunately HJK does not seem to have done a review on them. My experience with the blue Tenergy cells has been lackluster. I will never buy them again.

Have you considered just buying a few and doing field tests?

13

I'd just replace that in series pair with a couple high discharge li-ion cells and a BMS. As a bonus, the tool's performance will increase considerably. In fact I did this to my hairclipper months ago and ;-) it rocks!

Parts list:

Cheers ^:)

14

My, 2.4-3v to 8.4v! Does it smoke much? :slight_smile:

I put some NiZn in a couple devices like that and they do work better, but that’s not nearly the voltage jump.

15

Nooo flydiver, I arranged the cells in parallel, enhancing torque (and robustness by a long shot versus :facepalm: 2S).

Cheers :-)

16

Ah, but of course. But, if they are parallel the function of the PCB is only charge/discharge protection?

17

Over, undervoltage plus overcurrent protection, flydiver. Lots of multi-cell BMSes do not have balancing logic but it can be added with inexpensive boards. Carefully wired multiple BMSes in parallel increase current handling if required, too.

Cheers ^:)

18

Now THERE’s a brilliant idea (I think) :+1:

What about a pair of these?

Efest 14500 800mAh Battery - Protected

They already have built in protection circuits?

Brand: Efest
Size: 14500
Chemistry: IMR
Nominal Capacity: 800mAh
Nominal Voltage: 3.7V
Discharge: 4A Max Continuous
Positive: Button/Nipple
Protected: Yes, PCB
Rechargeable: Yes
Dimensions: 53.20mm x 14.25mm
Weight: 20.9g

19

One thing……

Fully charged, the LiIo or IMR batteries would sit at around 4.2v

Two AA batteries fully charged would max at about 2.8v

That’s a differential of about 1.4v or the equivalent of an extra battery.

Not sure how the motor and simple vacuum circuit would like that extra voltage.

20

That’s where the improved performance comes from that barkuti was talking about. :slight_smile:

21

But…But….you left out the critical line…….

“Not sure how the motor and simple vacuum circuit would like that extra voltage”.

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One way to find out…

23

One big problem with those Efest cells, Zebretta, is they're low drain. Big no! If the vacuum cleaner really pushes current a couple 7+A continuous cells in parallel is going to be required (extra rpm requires extra torque).

Not sure how the vacuum cleaner circuit will deal with the extra voltage? What :-D circuit?

All I had to deal with for my hairclipper mod was, essentially, the removal of some cell recharge current limiting components and rewiring plus resistor value adjustment for a power-on red led. ;-)

Originally posted on Mon, 10/30/2017 - 06:44; little fix.

24

Yeah, but he’s trying to use 2 Tenergy Blue NiMh to power it. I seriously doubt those cells have a lot of amp output. I’ve got some OLD ones (very old so very tired), but they are lousy. I had some NEW Tenergy Blue D-cells and they were lousy too.

25

yea, blue cells are not that good, premium or lsd centura are better.

there is no need for any circuit with nimh cells, assuming your cells can supply current needed. when voltage drops below 1v they supply almost no current, and your device simply wont work.
also if you need to pull 7A from aa cells forget about tenergy, you need elite

26

A little story worth being told:

For my hairclipper initially I replaced its dieing stock low capacity AA NiMHs, but there was a catch: the stock AAs were rugged overcharge tolerant industrial cells, the lack of a true charging circuit inside the appliance killed the newer high power Tenergy AA 2500mAh cells I stuck inside at first FAST (overcharging).

If Zebretta's vacuum cleaner does not have proper -dV/dt Ni-MH charging logic inside, the newer AA cells' life is going to be rather short.

If high voltage is a concern, another alternative could be using two 14500 LiFePO4 cells in parallel, there are 1S BMS circuits available for this (a couple of these would do for ≈10A combined).

Example: Soshine 14500 LiFePO4 700mAh (gray) @ lygte-info.dk

Above 500mAh of capacity even if discharged at 5A, with more than twice the voltage output of the best Ni-MH AAs when discharged at 10A. Sounds like a noticeable performance increase, even if the effective capacity would only hover between 1000 - 1100mAh.

FastTech has Soshines and Powerlions in stock, Soshines with a lil bit more capacity and Powerlions with a tad better discharge rate if I do remember right, the long ago published review in this regard on the forum is now missing the graphs: Test / Review: Coolook, Powerlion and Soshine 14500 (AA) LiFePO4

Hope this is of help.

Cheers :-)

27

Thanks for ALL the replies !

Ok, today I actually measured the current draw.

So, my “HIGH current drain vacuum” uses………

1.5A startup
0.7A running

lol
“the sky is falling”….“the sky is falling”…… :person_facepalming:

Sry guys, I was estimating. I thought it would be more.