Yep Totally agree. I use several of these to monitor voltages and currents in my DIY EV. Nice thing about them is that they work both ways and will take into account regen and charging as well as discharge. I found them to be as accurate as shunt based meters at a similar price range BTW.


On 13/03/2019 17:39, Jay Summet via EV wrote:
I would recommend buying an inexpensive amp hour / voltage / watt hour meter and using that to monitor the battery. (The one I use records the data it has logged when power is removed, so that when you apply power again the AH counter keeps the last reading.  You can also buy them with relay outputs that allow you to program a "low voltage disconnect" to act like a very basic BMS protection circuit...but the low voltages is based off of the entrie pack, not the individual cells....)

This is the one I used on my last project:

(It does not have relay outputs, but does support up to 200AH with it's current sensor...which was important for my project).

You may wish to choose one with a 100 AH or lower current sensor if you will be testing at lower currents, as the accuracy of the current sensors is usually a percentage of their max rating. (Also note that a shunt based current sensor is more accurate than these magnetic sensors that you put the wire through, but if you are trying to get a very accurate measure you probably are not buying $30 meters.....)


On 3/13/19 10:21 AM, Dan Baker via EV wrote:
I have been communicating with a couple sellers now on Aliexpress.  Prices
seem quite varied and reviews are mixed on these batteries.  I suspect
there isn't a lot of standards or testing on actual claimed capacities.  I would like to try a 12v pack or 2 before buying more and perform some tests to verify capacity.  Has anyone done this testing before?  I assume the ah
rating is based on a 1amp draw for x amount of claimed hours. So would I
hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
till below 12v?  Or would I measure it till the BMS protection cuts in -
(9-10v?).  Some reviewers have found packs listed at 100ah capacity to
actually have only 30ah cells inside, lots of misinformation.

Thank you,

On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV <> wrote:

On 3/12/19 9:59 AM, Dan Baker via EV wrote:

If I don't charge with my Sevcons and use the included individual 12v
chargers, would there still be worry of connecting too many in series?
it charging,discharging or both the issue when connecting in series?

That depends entirely upon the battery model/manufacturer and the specs
for that specific battery.  If there is an issue, it would most likely
be an issue for both charging and discharging.

The thing to watch out for is if the batteries have a MOSFET (solid
state switch) that is used to disconnect the battery when charging (done
charging, voltage too high) or when discharging (voltage too low).  In
many cases, the MOSFETS are not rated for super high voltages. It may be
twice the working voltage or much higher (24,36 or perhaps 60 volt
rated).  If your series pack goes above the MOSFET rating, it is likely
to fail spectacularly (short closed in the worst case) when it is asked
to disconnect the battery.

If the batteries use relays or contractors, they may or may not be rated
for higher series voltages, you need to verify.

In short, the electronics that are making these batteries "drop in
replacements" for a 12 volt battery are designed to work at that voltage level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the
system was not designed for high voltage (72-144 or higher) to be seen
by the battery.

The BattleBorn batteries for example use 60V electronics, and are rated
to be used in series up to a 48 volt system (They were designed this way
to be a drop in replacement for 12, 24, 36 and 48 volt solar power
systems....but many "auto starter" or RV replacement batteries gave no
thought about using more than one in series, or if they did, it was only
up to a 24 or 48 volt level.)


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