Battery: association and reloading

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Boris591
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Battery: association and reloading




by Boris591 » 22/06/08, 21:01

Bonjour à tous

I'm working on an electric bike project.

its motor would be (for the moment) a 1200W 48v

the desired autonomy being of one hour, it would therefore be necessary (at least) a capacity of the batteries of 25 Ah

This is where it gets harder : Cheesy:

first question about the capacity of the batteries.

Unless I'm mistaken, I can put a battery of 48, or two of 24v, 4 of 12 v .... (in series)

So I would like to know first, do the capacities add up too? (Basically can I put two 24v 15Ah batteries in series, or 4 12v 8Ah batteries for example in order to respect my "specifications")

then concerning the reloading

in the case of the use of several batteries in series, can we
connect each battery to independent "sources"?

ex: with two 24v batteries in series, recharge the first with solar panels, the second with a wind turbine (bah what on a bike it can be beautiful : Cheesy: )


here I hope you can help me, but do not worry if it may seem crazy to you, but for the moment I am looking for theoretical solutions and I am trying to understand the basics

thank you :D
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crispus
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by crispus » 22/06/08, 22:40

Hello,

I am far from being a specialist in VAE, although it does tempt me a lot for short trips.

1200 W seems huge, a quarter should be enough, right?
In addition the power is not used continuously, unless you always go up : Mrgreen:

So for your energy calculation take an average value based for example on 3/4 of the nominal power multiplied by the rolling time, without forgetting the engine efficiency. Unlike heat engines, red light stops don't count: cool:

For batteries, whether in series or in parallel, the capacities and energies stored are always added: 8 Ah x 4 = 48 Ah.

An 8 Ah battery under 12V corresponds to an energy of 8x12 = 96 Wh. Or 384 Wh with 4 batteries.

Then, series or parallel, it depends on the motor: the more you go up in tension the more the current decreases, and the section of the cables too. So mounting batteries in series is preferable.

Another advantage of the series connection is that each battery can be recharged separately by a "floating" charger. The most sophisticated compare the voltage of each cell (2V for lead) and recharge the weakest by taking the energy from the most charged, which balances discharges and seriously prolongs battery life. It's the imbalance that kills them.

When the motors were supplied by contactors, a nominal motor voltage was taken which was identical to that of the batteries. Now, to give the electronics sufficient margin, the motor nominal voltage must be slightly lower than that of the batteries. It also allows to have an "overboost" function which gives a temporary supplement of power. It can still be used ... And even at the end of charging, there is sufficient voltage for the motor.

Ex for 48V of batteries I would take 42V motor "with the ladle"
The dangerous limit for humans in direct current is 60V DC in a humid environment, better to stay below and limit yourself to 4 batteries in series.

That's still a first answer, but there are user-designers on this forum who will be happy to complete or even rectify all of this ...

Good project! By wishing that it succeeds ...
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by Woodcutter » 22/06/08, 23:25

Crispus wrote:[...] I am far from being a specialist in VAE, although that tempts me a lot for short journeys.

1200 W seems huge, a quarter should be enough, right?
In addition the power is not used continuously, unless you always go up : Mrgreen:[...]
Well, it's mostly totally illegal! : Shock:

An eBike cannot see a motor of more than 250 W and, in practice, since we are talking about pedaling assistance, it is indeed more than enough and in any case more important than what a man can provide " normal "continuously over a long period.

For comparison: E-Solex 400 W
Scooter "50 cm3 equivalent" from 800 to 2000 W approximately
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by Christophe » 22/06/08, 23:30

Woodcutter wrote:Scooter "50 cm3 equivalent" from 800 to 2000 W approximately


Uh, I don't know a lot of 1hp scooter on the market, it's 4 to 5 now.

The 103 was 3.5 if I remember correctly ...
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by Woodcutter » 22/06/08, 23:53

Christophe wrote:
Woodcutter wrote:Scooter "50 cm3 equivalent" from 800 to 2000 W approximately


Uh, I don't know a lot of 1hp scooter on the market, it's 4 to 5 now.

The 103 was 3.5 if I remember correctly ...
Yes, now and in thermal, but electrics are very powerful. The 103 was more like 2.2.
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by chatelot16 » 23/06/08, 02:45

in series the capacities in Ah are not added: it is with the addition of the voltages that the capacities in wh are added

so you need 4 battery 12v 25ah in series

but the duration of 1 hour will be very theoretical: a battery gives its theoretical capacity in very slow discharge

in 1 hour it is too fast the capacity actually available will not be even half, and the battery will wear out quickly

it will be necessary to put bigger to have a reasonable lifespan

you must recharge all the batteries in series with the same current

if the battery was charged separately, it would be necessary to monitor the voltage of all the batteries during the discharge to stop as soon as one of them is almost empty
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by crispus » 23/06/08, 09:03

chatelot16 wrote:in series the capacity in Ah is not added

Oops! Too much relaxation on the WE ... Thank you for correcting this gross error. : Oops:
it is with the addition of the voltages that the capacities in wh are added
However, reread this sentence, it contradicts the previous one : Lol:

if the battery was charged separately, it would be necessary to monitor the voltage of all the batteries during the discharge to stop as soon as one of them is almost empty

This is the whole point of a "floating" charger, but it was actually beside the question.
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by Boris591 » 23/06/08, 11:14

Crispus wrote:
An 8 Ah battery under 12V corresponds to an energy of 8x12 = 96 Wh. Or 384 Wh with 4 batteries.



thanks for his answers

so first a note: I will certainly be able to target less than 1200w, but in reality it's more than pedaling assistance that I want .... in fact it's a scooter if you want ^^


so then if I understand correctly, the Ahs are not added, which means that 4 batteries in series do not have 4 times the capacity of a battery in terms of ampere (it seemed a little too good too. ..)

here like 4 battery in series gives me 384 Wh, so I would actually need 16 8 Ah batteries to have the desired autonomy ?? (regardless of the voltage at the moment, I'm only talking about autonomy)

I would be roughly in the 50 kilos of battery there not cool
: Mrgreen:
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by chatelot16 » 23/06/08, 12:56

yes not light the batteries

and in addition this result is only theoretical: to discharge in one hour it is too short for lead acid batteries it uses them too quickly and they would not even give half of the theoretical energy

nicd or nimh batteries are a little more efficient in rapid discharge, but much more expensive

and lithium batteries are too expensive for me ...

to make something durable with lead you need much bigger batteries and try to compensate for the additional dead weight by a good energy recovery in the descents

you also need wheels that support the load without loss of energy: the small scooter wheels are worth nothing: it is better to have large and narrow wheels on a real motorcycle
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by Boris591 » 23/06/08, 14:00

so the idea would be mainly to recover energy.


is it possible to charge a battery (from a source like solar panel or other) while using it to power the engine?

I don't think it's possible ... :frown:


the idea would then be to have two separate power supplies: one that would power the motor, another that would recharge (powered by dynamos, solar panel and I don't know what else)

and as soon as one of the batteries (or group of batteries) is too low, the assembly will switch to the second power supply group

(and the first set of batteries will recharge in turn)

is it easily achievable? how would the editing be done?

please :)
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