24V to 36V overvolting

[rahulgupta32]

Hi all,

I recently posted a thread about the Yescom 24V 500W kit not working and am happy to announce that it works now. The controller seemed to be bad.
I replaced the controller and everything is fine.

I guess i really am a newbie, and have experienced a below satisfactory performance out of my kit. I bought the 24v Kit because i did not want to spend too much into the batteries. I have two 12V 12Ah batteries in series. I only have to go 4 miles total in a day and range is not an issue for me.
I am young and recently married and want to save some dough for my future.

I would however want to increase the performance of my ebike without spending too much money.
I am thinking of buying another 12 v battery and putting that in series with my setup to get 36v.

I am pretty confident that the motor can take it as i do not have hilly areas for my commute.
I do not know how the controller will behave. I need some advise on this.
I am not worried about the LVC as i will not drain the batteries to cause damage as they only have to go 4 miles before i charge them.

I do not know if the controller has a maximum voltage cutout.

I seek any veterans with advise. I searched the forums but did not find a similar post for help.

Thanks in advance.

 

[rahulgupta32]

Really no-one has tried this?

 

[arkmundi]

I advise limiting battery size to the voltage/amperage rating of your motor. There is some tollerance of the motor/battery to handle out-of-spec ranges, but I wouldn't press it. Why? You're usually not improving performance much and may well decrease the longevity of one or the other.

 

[d8veh]

I've over-volted nearly every bike I've had and not had a problem yet. Over-volting can't damage the motor, but you have to be mindful about how much power you put through it so that it doesn't over-heat.
My guess is that you just add another battery and enjoy the extra power, but if you want to be sure, you have to open up the controller and check that you have capacitors rated at 50v or more (writen on them) and try and read the number on the FETs so that you can look up the data sheetfor their voltage rating, but having said that, every one that I've checked has always been OK.

Some controllers have a high voltage cut-off, so if the voltage is too high, it won't work. You can test by connrcting any 12v battery in series with yours. You can run some jump leads from a friend's car.

The only downside is that the low-voltage control will be too low for your batteries so that the system will try to over-discharge them, which is not good for their long life. You can get round it by mounting a voltmeter on your handlebars and switching off manually at about 31.5v.
http://www.ebay.co.uk/itm/Waterproof-Digital-Voltmeter-DC-15V-To-120V-Red-Led-Voltage-Digital-Panel-Meter-/180888615101?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1dcd38bd

 

[Gregory]

Agree with d8veh.

And just in case you have one of those throttles with battery LEDs, obviously they will not work correctly at 36V.

 

[Jeremy Harris]

My guess is that this will be pretty safe to do, as it's very unlikely that a 24V controller would have any components rated at less than 40V. As you're running on SLA batteries, the voltage will drop very quickly under any load, plus even the hot off charge voltage will only ever be as high as about 43 V or so at the most, and I've not yet seen a 24V controller that uses components with ratings lower than this.

Allowing a 50% increase in battery voltage is a specific case for a low voltage controller like this though though, the higher voltage controller most certainly do run into problems when the voltage is increased significantly. The less than obvious problem in many of them isn't the component ratings (they are easy to check), it's that the first stage voltage regulator is often only rated for 40V absolute maximum input. Most of these controllers use a series resistor to drop the battery voltage to a safe level for the regulator and the value of this resistor is highly dependent on rated battery voltage. If the battery voltage is increased significantly on one of these higher voltage controllers (pretty much anything rated at 36V or more) then it is very likely that the first stage voltage regulator will receive too high an input voltage and either fail, or suffer from greatly reduced reliability. It's an easy fix though, one that's been documented here on the forum years ago. Just change the big resistor for one with a higher value and this brings the regulator input voltage back into spec.

 

[arkmundi]

Its not voltage that matters but current and current delivery. Over-volting an e-bike is usually undertaken to improve current delivery and the performance improvement in most cases is due to that. A high C battery (like my A123 AMP20) does that for me and the performance improvement was significant compared to my old SLA battery. No lag going up those hills at full throttle. Great continuous C and burst C.

All electrical circuits, whether they are at home, on an e-bike, in a computer or whatever are built to an amperage specification, so the wires, the connectors, and in this case a controller. Yea, you may be get away with it, but why? Some say its safe and OK, but in their experience. I'm sure there are cases, often not reported where some component or other was fried, over time by passing too much current through a component where the wires can't handle it.

Then there's the cost factor of adding in more cells to get to the voltage. If a bike has a motor and controller built to 24 volt specs then its built to deliver some current level, 20 amp or whatever - its usually explicitly stated, in the manual or on the component label. Save youself long term cost of ownership and hassel but staying within spec.

 

[Jeremy Harris]

Increasing the voltage won't have any effect at all on the controller current limit though, so the motor won't see any more current and won't run any hotter. Rather than the motor BEMF limiting current under some conditions the controller will be able to do it (and likely allow the motor to draw current to the limit under a wider range of conditions). This is how it should be for an efficient system, especially when you factor in that battery current will be reduced for any given power output with the higher voltage system (because the controller works as a very efficient buck converter).

 

[arkmundi]

My guess is that this will be pretty safe to do, as it's very unlikely that a 24V controller would have any components rated at less than 40V.

Perhaps, perhaps not. If in doubt and it matters, then find out if you can. Remember, once you've over amped a component and it fries, you usually looking at replacement rather than repair. Safe, pretty safe, not-so-safe and unsafe are attributions in hind-sight. Foresight is better.

 

[dogman dan]

Go for it. Worst thing that can happen is you have to go buy a 36v controller. But it's unlikely that they have 30v caps in that controller, so very likely it will be fine.

Brace yourself though, you won't stop spending money till you reach 40 mph if you are like many of us. Somehow, you just keep going, "this is nice! but I still want more ".

 

[Jeremy Harris]

My guess is that this will be pretty safe to do, as it's very unlikely that a 24V controller would have any components rated at less than 40V.

Perhaps, perhaps not. If in doubt and it matters, then find out if you can. Remember, once you've over amped a component and it fries, you usually looking at replacement rather than repair. Safe, pretty safe, not-so-safe and unsafe are attributions in hind-sight. Foresight is better.

Even better is knowing that components come in a limited range of maximum voltage ratings. The capacitors, for example, will be either 50V or 63V, as they are the preferred values above 25V (they'll probably be 63V, as more often than not they are cheaper). The chances of having a weird value are low, as these things are built right down to a budget and the preferred value components are cheaper than oddball ones,

 

[d8veh]

The less than obvious problem in many of them isn't the component ratings (they are easy to check), it's that the first stage voltage regulator is often only rated for 40V absolute maximum input. Most of these controllers use a series resistor to drop the battery voltage to a safe level for the regulator and the value of this resistor is highly dependent on rated battery voltage. If the battery voltage is increased significantly on one of these higher voltage controllers (pretty much anything rated at 36V or more) then it is very likely that the first stage voltage regulator will receive too high an input voltage and either fail, or suffer from greatly reduced reliability. It's an easy fix though, one that's been documented here on the forum years ago. Just change the big resistor for one with a higher value and this brings the regulator input voltage back into spec.

Is there a way of working out the new resistor value? I heard that the regulator uses it on a divider somehow to get the right output voltage. Is this right?

 

[Jeremy Harris]

Is there a way of working out the new resistor value? I heard that the regulator uses it on a divider somehow to get the right output voltage. Is this right?

Yes, it's pretty straightforward. Many controllers have a quiescent current of around 50mA when powered up and everything connected, but with no throttle signal (you can measure this to check it easily enough). The maximum allowable input voltage into the first stage regulator is 40V, the minimum is around 16V to 18V to ensure good regulation. The voltage dropped across the power resistor (or resistors, some controllers use two or three resistors in series/parallel to reduce the heat per resistor) is given by Ohms Law. Here's a worked example that may help:

Say you have a 62V maximum input voltage from the hot-off-charge battery pack. The voltage drop needed across the resistor(s) has to be at least 22V to keep the input to the regulator under 40V. If the quiescent current is 50mA (0.05A), then the resistor value needed to drop 22V would be 22 / 0.05 = 440 ohms. The nearest preferred greater value resistor is 470 ohms, which would give a voltage drop of 470 x 0.05 = 23.5V, which is OK.

As a double check, you need to make sure that the resistor value won't cause the voltage at the regulator input to drop too low when the battery runs down. Say your minimum battery voltage on this 62V maximum pack is 52V. 52V, less the resistor voltage drop of 23.5V gives 28.5V at the input to the regulator. This is above the minimum of around 16V to 18V and so is fine.

Finally you need to check the power dissipation in the resistor, to make sure it isn't going to run too hot. Ideally you want no more than around 1 to 1.5W per resistor to keep things just tolerably warm, maybe a little less if your controller tends to run hot in use. The resistor power dissipation is just the voltage drop, 23.5V in this case, times the current, which gives 23.5 x 0.05 = 1.175W, which is just about OK for a single resistor. The resistor should be over-rated with regard to power, as it's inside the sealed controller case, so use a 2W, or even 3W, rated one to be safe.

 

[rahulgupta32]

THANKS TO ALL FOR THEIR REPLIES. I WILL TRY THE 36V AND POST MY RESULTS

 

[rahulgupta32]

I have added the 12v battery to my 24v pack to make it 36 and ran on the same controller and motor. No problems whatsoever. The additional power is awesome.

I guess the 36V systems has enough Umph for me.

I just need to figure out how to balance my batteries now. 2 are at 13.6v and the third is at 12.6.

Thank to all for their help.

 

[Lucifer]

I have added the 12v battery to my 24v pack to make it 36 and ran on the same controller and motor. No problems whatsoever. The additional power is awesome.

I guess the 36V systems has enough Umph for me.

I just need to figure out how to balance my batteries now. 2 are at 13.6v and the third is at 12.6.

Thank to all for their help.

Hi, I know this is an old thread, but I'm thinking of doing the same thing, (but with Lithium batteries, cos I got them) I wondered how it worked out in the longer term?

 

[Lucifer]

My guess is that this will be pretty safe to do, as it's very unlikely that a 24V controller would have any components rated at less than 40V. As you're running on SLA batteries, the voltage will drop very quickly under any load, plus even the hot off charge voltage will only ever be as high as about 43 V or so at the most, and I've not yet seen a 24V controller that uses components with ratings lower than this.

Allowing a 50% increase in battery voltage is a specific case for a low voltage controller like this though though, the higher voltage controller most certainly do run into problems when the voltage is increased significantly. The less than obvious problem in many of them isn't the component ratings (they are easy to check), it's that the first stage voltage regulator is often only rated for 40V absolute maximum input. Most of these controllers use a series resistor to drop the battery voltage to a safe level for the regulator and the value of this resistor is highly dependent on rated battery voltage. If the battery voltage is increased significantly on one of these higher voltage controllers (pretty much anything rated at 36V or more) then it is very likely that the first stage voltage regulator will receive too high an input voltage and either fail, or suffer from greatly reduced reliability. It's an easy fix though, one that's been documented here on the forum years ago. Just change the big resistor for one with a higher value and this brings the regulator input voltage back into spec.

Hi,

I know this is an old thread, but it came up on Google, when I was looking to do this to a 24v bike (but with Lithium batteries, as I have 36v Li batteries) Not tried them on the 24v bike, though, the 24v bike feels underpowered. As you replied to this post on various considerations (but using sla batteries), anything you would change or ad if I was doing the same thing Li Batts.

Keith AKA Lucifer