Extending the length of wire on the charger

[stone]

Would I be able to extend the length of cable ( the output side ) on a standard battery charger for a 48v bike by about 15 -18 meters?

I am trying to charge my ebike from third level up and leaving the power cord is not possible.

Is there any safety issues in doing so? Its a small walkway downstairs and the wire would not block the 2nd level windows. I was thinking of fusing it to 1 or 3 amps and it can be monitored from upstairs and the wire dangling from upstairs would just be a charging plug.

Would there be any resistance issues etc, electrical problems?

thanks in advance

 

[ZOMGVTEK]

15-18M?!

It would 'work', but it's most likely the battery won't be quite as charged. How much of an issue this is depends on the charger, and resistance of wire used. At 1-3A it shouldn't be too bad, but thats a lot of cable to add on to a charger.

Is this a SLA battery? You can try it out and see what kind of voltage drop you get. If the charger tapers off towards the end of charge and sits at float voltage for a while, the impact should be minimal, but it will take a little longer to charge.

 

[dnmun]

yes, it will work. the voltage drop will fall to nothing when you get to the final charging voltage and it is using just the balancing current. if it is a 5A charger you could go as small as 18-20 gauge 2 wire even, but reduce if you push more current than 5A. imho

 

[Chalo]

If you look up the resistance rating for your chosen wire, and you know how long the leads have to be, you can calculate the voltage drop for any given amp load. As the load tapers off towards end of charge, so will the voltage drop.

48V is not considered low voltage from a building code standpoint, so your wire installation would probably constitute a violation of local ordinances. It sounds like a super hokey setup to me. Why not encase your batteries and bring the case inside to charge it? That would make your bike less theftworthy too.

Chalo

 

[stone]

Thanks for all the replies. What if I shorten the amount needed to 8 - 10meters? I have a patio and I could try to put it just by the corner of the yard. Would that work then or is it still too long? I know nothing about resistance but I can buy thicker 2.5mm 10awg cables if it is going to help.

I do not think it is a good idea to dangle a power strip, there could be people who might overload it, steal it, get hurt by it, etc.

 

[cal3thousand]

If you are going to increase the length of that wire, you had better increase the copper too.

The added length is just added resistance. Mitigate that with a lower gauge cable like 8 AWG or 6 AWG.

 

[ZOMGVTEK]

You definitely don't need 6 or 8 AWG for a few amps at that length. 12-14 gauge should be fine. The shorter the better, but at the length you need and the currents involved, it won't matter that much.

If you have 10 gauge on hand, that would work great, but I would swing for 12. If the charger is 'smart' enough, it will work fine even with 18-22 gauge or so, just take longer to charge... Possibly much longer.

 

[cal3thousand]

You definitely don't need 6 or 8 AWG for a few amps at that length. 12-14 gauge should be fine. The shorter the better, but at the length you need and the currents involved, it won't matter that much.

If you have 10 gauge on hand, that would work great, but I would swing for 12. If the charger is 'smart' enough, it will work fine even with 18-22 gauge or so, just take longer to charge... Possibly much longer.

He's right. I just checked a calculator:

http://www.cirris.com/testing/resistance/wire.html

for 30 feet of 14AWG, the resistance is only .076 Ohm. Not enough to worry about.

 

[ZOMGVTEK]

We can look at a few numbers to express the losses a bit better...

Assumming worst case, 18M, or 59.0551ft, 20 gauge will be about 0.599 ohms, and it would be realistic to assume the additional wire will be soldered on to bare wire, possibly adding .025 ohm or so. Total is .625ohm. Assuming worst case, 24 cell PB at a float voltage of 2.55V/cell, we have 61.2V coming out of the charger. The line loss would be 1.875V at the full 3A current. I would consider this substantial since it would shift the chargers stages dramatically earlier, taking longer to charge or charging to a lower SOC which tends to be bad for SLA. Along with likely lower durability from the thinner gauge cable...

12 or 14 is probably about right. But yeah, thinner or thicker WILL work to varying degrees. You don't want to have super thick cables hanging that far, and thin stuff can be just as bad.

 

[dnmun]

if the parking spot is 60' away, you have 120' of wire.

so if using the 20G calculation, using 1.2ohm total resistance at 50 mA of balancing current the voltage drop would be .06V between the charger and the battery.

if this is a 16S BMS on a lifepo4 pack then that is .004V/cell difference in the cell balancing voltage.

of course you could adjust the charger voltage up by the .06V if you need to.

 

[dogman dan]

That is a long wire. I do agree that it wouldn't take huge 8g for that amps of DC.

You might look at wire for DC outdoor lighting setups. It's plenty thick enough, and more importantly, designed for outdoor exposure for its entire service lifespan. Don't get cheap indoor speaker wire.

Even If heavy sla's I'd just lug the battery up to the house.

 

[dnmun]

if you look inside your charger you will see that they use 18G wire for the charger leads. that will work for the drop down to the courtyard. use solid, 2 wire, and maybe it will cost about 12 yuan for the entire length. if you can find a deal, or maybe up to 20 yuan. if you go to 8 gauge wire like these guys say it will weigh about 50kg and you need a lot of support to hold the wire, and it will cost about 300 yuan.

 

[stone]

thanks for the replies, I went to to look for cables yesterday, the thick ones are aluminum coated with a layer of copper. They do not have pure copper wires. I think I would try online. A pity cat 5 cables wont work because it got 300meters of it.

The battery I have are SLA and the elevator is too small to fit a larger bike ( who would have thought).
I did not consider bringing the battery up because it is over 25kg and if the casing cracks, I cannot get a replacement because this bike is brought from another city and cannot be found in peking.

I cannot find those good prices in shops somehow.

 

[tony67]

I have done this with my 48v 4 amp lifepo4 charger. I added approx 10 metres to the output side of my charger using a standard garden extension lead. It takes slightly longer to charge the battery. I've not done the calculations but its obviously to do with the resistance in the wire. I would advise making an extension with andersons or some other connector so you can still use your charger in its standard length in case you need to take it out with you in the future. I've been using it this way for almost a year now with no issues.

 

[999zip999]

Put a timer on it so as not to leave 48v live to long downstairs.
Save money for a lifepo4. Then carry it up for safety. Lead is dead.