Battery calculation

[Nixtoo]

Hi,

Someone posted in a thread a calculation to work out how much of the battery had been used. It had something to do with timing how long it took to recharge, but I can't find it. Can anyone help me?

Thanks

 

[D8ve]

Simple find the A charge rate of your charger. One hour of one amp is one Ah in the battery. (Slightly less but it's a rough guide)
So 2 amp charger will half charge a 12 Ah battery in 3 hours

 

[Alan Quay]

Simple find the A charge rate of your charger. One hour of one amp is one Ah in the battery. (Slightly less but it's a rough guide)
So 2 amp charger will half charge a 12 Ah battery in 3 hours

That assumes that the charge current is constant, which it isn't. A 2A charger will be putting out 1A for fair time depending on where you catch it in the cycle.



Sent from my HTC One_M8 using Tapatalk

 

[D8ve]

Yup a rough guide. The last half hour of some bms,s can be balancing. But the man wants a simple approximation. We can measure the milli watt etc.
Still quick ish is to time flat to full and then decide by time but I,m not a pedant

 

[Nixtoo]

That's really helpful thanks. It's a 2A charger. I noticed it had gone green after 3 hours (wasn't watching that closely). So that's a max of 6Ah back into the battery. It's a 10Ah battery, so the indicator showing 2 out of 5 bars was fairly representative.
I'm still learning what it can do, but really don't want to push it as the final bit home is always up a big hill! Not a place to run out of juice!

 

[awol]

You can also use one of those plug-in energy monitors which gives you the total watts used to charge the battery, I then knock off 20w per hour of charge as that seems to be what the charger itself uses. Probably first drain the battery to totally empty and see how many watts it takes for a full charge first as a benchmark.

 

[Fordulike]

If you're handy with a soldering iron, why not wire in a precision power analyzer.
Then you'll know exactly how many amp hours you've used:

Precision Power Analyzer

It's a bit of a poor man's Cycle Analyst, but it does the job.

 

[Kinninvie]

If you're handy with a soldering iron, why not wire in a precision power analyzer.
Then you'll know exactly how many amp hours you've used:

Precision Power Analyzer

It's a bit of a poor man's Cycle Analyst, but it does the job.

Ignore the words "high precision" though,I have 3 of these and at 48 volts, one reads 46.2v,the second reads 47.1V and the third reads 48.4V.
They are perfectly adequate as a rough guide though and I use mine on Meanwell power supplies to keep track of charging levels.
I have a Cycle Analyst on my bike now but they are a bit expensive at £115 delivered to the UK and dont forget the import duty either.....FedEx just sent me a bill for £29 !!!

 

[Fordulike]

Ignore the words "high precision" though

High precision to Chinese standards

The Cycle Analyst is an awesome bit of kit. More suited to hardcore modders, than the casual cyclist though, due to the cost.

 

[Nealh]

I had a 150a power meter and it was truly awful on 10s charged to 41.6v it over read by 7v and told me I had 48.6v, I now use the blue 60v/100a watt meters and they are spot on.