Chargers on a timer

Batteries, Chargers, and Battery Management Systems.
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KarlJ   100 W

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Chargers on a timer

Post by KarlJ » Mar 20 2014 5:51am

Can anyone confirm if this will / wont discharge the battery if connected without being connected to the mains?

to be specific
http://em3ev.com/store/index.php?route= ... uct_id=139

I ask as i'd like to have the charger on a timer so it only runs during off-peak times.
Peak rate for power for me is 48.8c/kWh and off peak is 14c/kwh.

difference of which is worth 16c per charge (assuming 100% efficiency which im sure its closer to 70% given the fan in charger etc) over say 1000 cycles is 1/3 of the way to the next pack!

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friendly1uk   10 MW

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Re: Chargers on a timer

Post by friendly1uk » Mar 20 2014 6:08am

I can't be specific, but generally the pack won't discharge through the charger during a power cut. The led light may remain on though, causing a very minimal drain.
bmsbattery sent me broken and incorrect stuff, and won't even talk to me about it.

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dogman dan   100 GW

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Re: Chargers on a timer

Post by dogman dan » Mar 20 2014 6:11am

I wouldn't worry about it unless you bring the battery back completely drained. If that is the case, plug in for half an hour without the timer, then put it on the timer to finish later.

Hillhater   100 GW

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Re: Chargers on a timer

Post by Hillhater » Mar 20 2014 7:58am

KarlJ wrote:....which is worth 16c per charge (assuming 100% efficiency which im sure its closer to 70% given the fan in charger etc) over say 1000 cycles is 1/3 of the way to the next pack!
Seriously ?...you are worried about 16c per charge ?
You could probably save more than that just by changing your brand of toilet paper !
This forum owes its existence to Justin of ebikes.ca

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alsmith   100 kW

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Re: Chargers on a timer

Post by alsmith » Mar 20 2014 4:00pm

Stick an ammeter in one of the charge wires and measure any current flow when it is connected but switched off at the mains.

Gregb   100 W

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Re: Chargers on a timer

Post by Gregb » Mar 20 2014 11:27pm

unless you have a relay in it there will be slight discharge but I can't imagine it will be much. (that is why they are called semiconductors.. :). Do as suggested above. Even the cell log uses some power from its source unless you read the hack thread.....

deardancer3   10 kW

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Re: Chargers on a timer

Post by deardancer3 » Mar 21 2014 9:03am

alsmith wrote:Stick an ammeter in one of the charge wires and measure any current flow when it is connected but switched off at the mains.
If you calculate the discharge to be too much you can insert a properly spec'd Schottky Diode on a heatsink to prevent the discharge. you might have to increase charger voltage by one volt to compensate for the diode IR drop.
I had to do this on one of my chargers.

Or get a timer that delays turn on, but, does not turn off.



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KarlJ   100 W

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Re: Chargers on a timer

Post by KarlJ » Mar 21 2014 9:16am

16c a charge is 1/3 the way to next pack!
-but hey most of the time charging it FREE by the sun so you probably have a good point.

Solar panel FYI.....definitely does discharge the pack albeit slowly.

Now doing constant current constant voltage charging with it too, panels on a pallet and pallet jack, using 2 panels, simply push one or more into the shade and voltage will sit very close.watts up VERY handy here, in fact almost impossible without it to have any idea of what's up!

RACE on Sunday :) https://www.facebook.com/Freewaybikehike

backed off the controller to max 20A and dropped max speed to 95% 90% and 85% on the three position switch,
A)80km = cant got that far flat bikkie
B)charity event -everyone is a winner but don't want to thrash them excessively nonethe less.
C) probably guys fit enough to do the extra 500 odd W/hrs battery offers over 2 hrs anyway
D) main game is to find out

dnmun   100 GW

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Re: Chargers on a timer

Post by dnmun » Mar 21 2014 9:22am

the led will use a few mA, maybe 2-4mA and there is a draindown resistor across the caps on the output. the draindown resistor is about 5kR usually so for a 60V battery that is about 12 mA so maybe 15mA total.

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skeetab5780   10 MW

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Re: Chargers on a timer

Post by skeetab5780 » Mar 21 2014 10:07am

add a 120v coil 1 or 2 pole contactor off the load side of the timer and break the batteries positive connection to the charger. Or I guess you could just use 2 timers, whatever is cheaper. Some contactors are under 10 dollars.

dnmun   100 GW

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Re: Chargers on a timer

Post by dnmun » Mar 21 2014 10:54am

no need to do anything. 15mA is nothing to worry about.

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alsmith   100 kW

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Re: Chargers on a timer

Post by alsmith » Mar 21 2014 11:26am

It can seem quite surprising how quickly 'a few' mA adds up

15mA x 24hrs= 360mAh loss per day.

360mAh x 7days = 2.5Ah loss per week

A 10Ah battery will be flat in a month. Is that acceptable for usage patterns?

ie (depending on your battery capacity) don't leave the bike standing unused for much more than a couple of weeks, and charge it before riding if you've got a long ride ahead unless you enjoy pushing/pedalling.

For long periods of no use then charge periodically (based on your current draw and your battery capacity) or remove the source of any current drain during storage.

Punx0r   100 GW

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Re: Chargers on a timer

Post by Punx0r » Mar 21 2014 11:33am

I think the idea is to use it to charge overnight, so it will only be sitting idle and draining for a few hours until the morning.

dnmun   100 GW

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Re: Chargers on a timer

Post by dnmun » Mar 21 2014 3:01pm

you can open the charger and remove the drain down resistor if it bothers you.

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friendly1uk   10 MW

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Re: Chargers on a timer

Post by friendly1uk » Mar 22 2014 8:02am

It could actually be nice to drain down a fraction. You can have your charger balance them all up at full voltage, then the bleed down will just skim the surface charge a little. Sat at full voltage does them no good anyway.

As peeps have said, a relay or contactor that is driven by the mains electricity could be used to connect the battery too the charger. Thus when the power turns off, the battery is disconnected.

As well as saving a few quid, your helping the environment by using power off-peak. Sometimes power is just dumped at these times of day, so it is better to use that than have some made in the daytime just for you.
bmsbattery sent me broken and incorrect stuff, and won't even talk to me about it.

dnmun   100 GW

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Re: Chargers on a timer

Post by dnmun » Mar 22 2014 11:28am

if you are even more lazy and even more bothered by the loss of 12mA then you don't even have to remove the resistor, just cut one leg open and it won't conduct. how much easier can it be?

Gregb   100 W

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Re: Chargers on a timer

Post by Gregb » Mar 22 2014 8:02pm

I think alsmith (above) analysis of the situation is a very good point. We don't all use our setups the same way.

dnmun   100 GW

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Re: Chargers on a timer

Post by dnmun » Mar 22 2014 9:51pm

the original poster was talking about putting his battery on a charger overnight and then the other guy cooked up this thing about leaving it sitting on the charger for month and months. i think it has nothing at all to do with the OP's question.

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alsmith   100 kW

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Re: Chargers on a timer

Post by alsmith » Mar 23 2014 8:45am

just adding some scale into the question to aid perspective when making the decision...

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