48V Series Parallel LIFEPO4

[Sturdly]

I would like to split the pack and run parallel 24v discharge and 48v series for charging due to material on hand (got a Foxxpower pack and charger using an ebay coupon for an excellent price). Using 48v 8a BMS balancing charger on a 16 cell 48v 10a LIFEPO4 pack, cells rated for 4c continuous no battery BMS for discharging. Finding an affordable reasonably sized high amp DPDT switch is proving difficult and I like to keep things simple so I can understand what is going on. So am not really interested in relays and the additional circuitry they would require.

Would it be safe to use Anderson power poles to manually connect/disconnect the series and parallel circuits? Provided of course that I disconnect the controller as a first step in the switch over. Or is this a bad idea? Maybe someone can recommend a decent alternative. Would like to use this pack with my current 24v BB drive until I save up enough to get a BMC hub motor or maybe a cyclone 650 w if they prove efficient.

Thanks.

 

[Link]

Yeah, you could rig up a series/parallel harness with PowerPoles. I did this with one of my old packs, only it was for charging a 24V and 48V pack stuck together.

Though, really, a relay isn't much more difficult than a switch. Assuming the coil is the right voltage, it's only got one more pair of wires.

 

[Beagle123]

Hi:

I used Andersen's power poles to make a big plug where It connected 16 batteries in series then when I unplugged it, I charged at single cell level(4.2v). The biggest advantage is that you can't mess-up and connect it the wrong way because when you unplug it it dosconnects the batteries. It becomes physically impossible to have a mishap. It should be fairly easy to make your set-up:

You would create a square plug with 4 connections.

1) Make a fork in the leads from your controller so you'd have two potitives on top and two negatives on the bottom of the plug from the controller.

2) Likewise have each 24v battery have its positive lead on top and negatives on bottom. So when the battery plug and controller plug are connected, they are connected in parallel.

3) Make the matching charger plug so that there is a jumper wire connecting the negative of one battery to the positive of the other (series), then connect the remaining positive and negative to the charger. To charge, you unplug the battery plug from the controller and plug this charging plug into it.

Note that there is no way to mess-up and make a wrong connection because you can't plug in the charger until you've unplugged the batteries from the controller. You can't plug the plugs in backwards because the andersens connectors won't allow it.

This method of "sharing" a plug is excellent in my opinion because it is so foolproof.

The next issue you'll encounter is that you'll get sparks when you connect the batteries to the controller each time. This is because the controller has big capacitors in it that charge the instaant that you connect the batteries. You can get around this by installing a switch as a cut-off. Then when you plug in the batteries it won't spark. However, now the sparking will happen within the switch itself. This sparling is like welding and it will burn away the contacts of your switch quickly. So the solution is to mount aa button on your bike that bypasses the switch but has a 500 ohm wirewound resistor in it. This resistor will act as a shock absorber for the burst of current. So you'd press the button for a second or two allowing the caps to charge, then turn the switch on.

Get it?

Good luck

 

[Sturdly]

Thanks guys.

Beagle I really like your ideas but the charger actually has a built in BMS and separate circular connector with 17 wires and active connections, basically 1 wire per cell plus one extra for the final ground. The discharge is just single wires attached to each of the cells that start and terminate the series. So I can't make it totally monkey proof. Too bad as I'm sometimes a monkey.

I'm guessing that the switch for the resistor is to keep the battery from drawing when hooked up but the motor is idle. What gauge wire and amp rating momentary switch do you recommend?

Thanks again for the input.

 

[Beagle123]

I'm using this swich:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92688

It's very cheap, and I was very suprised to see how high-quality it is. It can handle any current I'm sure.

I'd reccomend using 10 guage wire for 30-35 amps or 12 guage for 20-25 amps. I know from experience that running 40 amps through 10 guage wire makes it pleasantly warm, but 40 amps would certainly heat up 12 guage wire. With a 20ah, 24v battery, you could be using up to 30 amps, but perhaps keeping it in the 20 amp range would be healthier for your batteries.

The purpose of the resistor and switch is to releive the high-voltage condition betwee the batteries and the caps. They "warmm-up" the capacitors with a constant charge so theyprepare to touch each other. YOu wantthe terminals be charged equally so they won;y create sparks.