Battery question.

[korky]

I have always been a light power user, until now, with 2x100ah Yuasa Efb leisure batteries, backed up with 120w solar panel and a recently fitted 70a battery to battery charger.I also have a NASA BM1 battery monitor and 600w inverter.
I want to charge my E-bike batteries when off-grid and stationary. They are 36v and rated at 16.7ah and 13.4ah repectively and use a 6a charger.
What's confusing me is the 36v bit. If everything was 12v it is easy to see there is plenty of reserve power in my leisure batteries. When I have tried limited off-grid charging the battery monitor shows a 20a discharge rate at the start. I know I can use the monitor to prevent me taking the leisure batteries too low but would be grateful if some one more knowledgable could provide the calculation, i.e. what state of charge would my full leisure batteries show after charging the largest bike battery from flat? I would not normally need to charge both batteries on the same day.

 

[wildebus]

I have always been a light power user, until now, with 2x100ah Yuasa Efb leisure batteries, backed up with 120w solar panel and a recently fitted 70a battery to battery charger.I also have a NASA BM1 battery monitor and 600w inverter.
I want to charge my E-bike batteries when off-grid and stationary. They are 36v and rated at 16.7ah and 13.4ah repectively and use a 6a charger.
What's confusing me is the 36v bit. If everything was 12v it is easy to see there is plenty of reserve power in my leisure batteries. When I have tried limited off-grid charging the battery monitor shows a 20a discharge rate at the start. I know I can use the monitor to prevent me taking the leisure batteries too low but would be grateful if some one more knowledgable could provide the calculation, i.e. what state of charge would my full leisure batteries show after charging the largest bike battery from flat? I would not normally need to charge both batteries on the same day.

I don't fully understand your question, but if it is about understanding the numbers, the maths is quite straightforward ...

Power (watts) is Power regardless of voltage.
you have a 36V battery. With X voltage, you will need Y current to add up to Z Power == > X * Y = Z
to get to that same Z power on a battery a third the voltage ie. a 12V battery, you need 3 times the current. In other words X/3 * (Y*3) = Z
in actual numbers, you have a 36V battery that uses a 6A charger. If that was a 12V battery, it would use an 18A charger to output the same Power.
with losses in conversion in a charger, seeing a 20A discharge when trying to charge a 36V battery with its 6A (@36V) charger makes perfect sense.

If you want to do a simple conversion, you have 2 36V batteries with a total capacity (at 36V) of 31Ah (16.7+13.4). the equivalent of that in 12V terms is 93Ah (31*3). If you used your full 200Ah Yuasa battery bank to charge these two eBike batteries from fully flat, you would use around 50% of the total possible capacity, and for those Yuasa batteries you have, you means you would use 100% of the total usable capacity as you wouldn't want to drop them below 50% od total capacity.
if you want to work out individually, just do the same maths e.g. Big ebike battery is 16.7Ah@36V, which is like 50Ah@12V, so a 1/4 of the leisure battery bank total, and 1/2 the leisure bank usuable - but add in losses in charging, etc.

 

[korky]

Thanks for that, just what I was looking for. Looks like a big enough safety margin when charging the largest battery. Most rides this will still be showing 2 bars out of 5 state of charge at the end of a ride, I don't foresee charging from flat ever but put that scenario forward to get the total state of discharge for my leisure batteries. It also explains the 20a discharge I was seeing on the monitor which had me puzzled.Much appreciated. If it ever stops raining I might ride the bleddy thing.

 

[r4dent]

How are you powering the 36v charger? I assume the ebike charger is 230v AC input. If so the simple method method will be to use an inverter which will add about 10% to the power drain.

To charge the smaller ebike battery from flat requires 36v x 13.4 ah = 482 wh, allowing 10% for the inverter = 520 wh
To charge the larger ebike battery from flat requires 36v x 16.7 ah = 600 wh, allowing 10% for the inverter = 660 wh
The usable capacity of your battery bank is (2 x 12v x 100 ah) x 50% = 1,200 wh.

For your 120w solar to provide 600wh (50ah) to replenish the 12v batteries. will require a day in Marbella in July / August or 10 days in Aberdeen in January.

 

[guerdeval]

Is it just me?, I’ve read the question, I’ve read the answers, I still haven’t a clue

 

[r4dent]

what state of charge would my full leisure batteries show after charging the largest bike battery from flat?

Charging the large ebike battery from flat takes 660 wh = 55 ah @ 12v

Nominal Capacity of the two leisure batteries combined is 2 * 100 ah = 200 ah
You will have (200 - 55) /200 % of your nominal capacity remaining = 145 /200 = 77 %.

Usable Capacity of the two leisure batteries combined is 2 * 100 ah / 2 = 100 ah
You will have (100 - 55) /100 % of your usable capacity remaining = 45 /100 = 45%.

.

 

[Sharon the Cat]

Is it just me?, I’ve read the question, I’ve read the answers, I still haven’t a clue

I can never ever get my head round this sort of discussion either.

 

[1 Cup]

How long have you had 36v bikes, But do you like the bikes ? If so a second battery . Or Faster charger ie 20 amp instead of 6 amps ! but what if !!!. You buy different voltage bike.

small invertor is opinion. For 20 amps for van ie 600w

I would open bike battery pack. especially if there stackers and charge at 12v I love 1820s

Why is 30 amp at 12v different from 24v or 36v ? The rest of this year will be sunny and like most vans, will not use its battery till night time as solar production will be higher so its charge bike time in daylight hours.

This is me chargein my 2 x 24v teasmaid kettle battery straight from van at 12v so I split it back to 12vs . no safety. Lol

 

[korky]

How long have you had 36v bikes, But do you like the bikes ? If so a second battery . Or Faster charger ie 20 amp instead of 6 amps ! but what if !!!. You buy different voltage bike.

small invertor is opinion. For 20 amps for van ie 600w

I would open bike battery pack. especially if there stackers and charge at 12v I love 1820s

Why is 30 amp at 12v different from 24v or 36v ? The rest of this year will be sunny and like most vans, will not use its battery till night time as solar production will be higher so its charge bike time in daylight hours.

This is me chargein my 2 x 24v teasmaid kettle battery straight from van at 12v so I split it back to 12vs . no safety. Lol

Had the bike nearly 3 years.Yes I like it very much.As stated it has 2 batteries.Bosch don't make a faster charger than 6a,it is plenty fast enough.

 

[korky]

How are you powering the 36v charger? I assume the ebike charger is 230v AC input. If so the simple method method will be to use an inverter which will add about 10% to the power drain.

To charge the smaller ebike battery from flat requires 36v x 13.4 ah = 482 wh, allowing 10% for the inverter = 520 wh
To charge the larger ebike battery from flat requires 36v x 16.7 ah = 600 wh, allowing 10% for the inverter = 660 wh
The usable capacity of your battery bank is (2 x 12v x 100 ah) x 50% = 1,200 wh.

For your 120w solar to provide 600wh (50ah) to replenish the 12v batteries. will require a day in Marbella in July / August or 10 days in Aberdeen in January.

The charger is powered by 600w inverter.

 

[trevskoda]

One thing you should do is double the solar, you only have half what you should have for the battery bank.

 

[colinm]

If you want to do a simple conversion, you have 2 36V batteries with a total capacity (at 36V) of 31Ah (16.7+13.4). the equivalent of that in 12V terms is 93Ah (31*3).

Is it just me?, I’ve read the question, I’ve read the answers, I still haven’t a clue

The clue is there, if you have 12v bike batteries they will take the same Ah out of you leisure batteries plus a bit for invertor/charger losses. 24v will be x2 (plus a bit) 36v x3 (plus a bit), 48v x4 (plus a bit)

 

[korky]

One thing you should do is double the solar, you only have half what you should have for the battery bank.

No,not doing that.The set up has been perfect for 6 years for my use. It is only now I have an ebike that the equation changes. Arriving at a destination with both bike batteries charged will give me 2 days riding, not accounting for some recharging of the leisure batteries while I am out for the day(in summer). Then when I move I have the B2B to top them off. Shoulder seasons and winter I will look at EHU if away more than 2 days or not travelling any distance between stops as solar is of little use then.

 

[1 Cup]

Solar runs your invertor OR THE B2B .so you have to go fast charging the quicker it charges bike battery's the longer the solar has to charge van Bank AT MAX HARVEST

Had the bike nearly 3 years.Yes I like it very much.As stated it has 2 batteries.Bosch don't make a faster charger than 6a,it is plenty fast enough.

Multi charger One hour or yours 6amp 3 hours or more. Bosch are not the only charging units for 1820 / LITHIUM cell

 

[merl]

Is it just me?, I’ve read the question, I’ve read the answers, I still haven’t a clue

I can never ever get my head round this sort of discussion either.

The OP essentially wants to know 'how many small batteries worth are there in his big battery'.
He can't work it out because they don't use an identical quantification system, one uses 12v and the other 36v, a bit like working out how many apples at 50p each you can buy with 10 euros, you need to convert either euros to pence or pence to euros or indeed convert both currencies to USD (which is what the suggestions above are doing when they convert both figures to watt hours).
You can get a very rough idea from the physical size of the batteries though, 10 times the size will very roughly mean 10 times the capacity.
(Heads down prepare for incoming remarks about power density, specific capacity etc etc) I said very rough ok!

 

[r4dent]

The OP essentially wants to know 'how many small batteries worth are there in his big battery'.
He can't work it out because they don't use an identical quantification system, one uses 12v and the other 36v, a bit like working out how many apples at 50p each you can buy with 10 euros, you need to convert either euros to pence or pence to euros or indeed convert both currencies to USD (which is what the suggestions above are doing when they convert both figures to watt hours).You can get a very rough idea from the physical size of the batteries though, 10 times the size will very roughly mean 10 times the capacity.
(Heads down prepare for incoming remarks about power density, specific capacity etc etc) I said very rough ok!

Incoming.

How many small batteries worth are there in his big battery?
Using the wh methodology
Useable wh of MoHo battery bank = 2 x 12 x 100 x 0.5 wh = 1,200 wh = 2
------------------------------------ ----------------------- ------
Usable wh of e bike battery 36 x 16.7 wh 600 wh

Using the volume comparison methodology
Volume of MoHo battery bank = 2 x 394 mm x 110 mm x 285 mm = 12,351,900.00 cubic mm =5.5
---------------------------------- ------------------------------------ ---------------------------
Volume of e bike battery 416mm x 84mm x 65 mm 2,271,360.00 cubic mm


Very rough indeed. The MoHo bank is over 5 times the size of the ebike battery, but only twice the capacity.

 

[merl]

BOOM
That'll be a 5:2 superior energy density of lithium over lead acid captain.

 

[Juan39]

Charging your larger e-bike battery from flat will use about 55 Ah from your leisure batteries, leaving you with around 45% usable capacity.