Increasing my 36v battery to 48v with booster battery

[steverebo]

my bike has a 10.4ah 36v battery my controller is a 24/36/48v one, i want to put a booster battery a lifePO4 12v 8ah one in series to increase my voltage to 48v as I don't really have £300 to send on a full replacement battery.

My commute is only 6 miles each way so battery won't drain and I charge daily.

I wanted to know if this is possible and is there a guide on how to do it.

 

[E-HP]

Yes it’s possible. You need to make or buy a series harness with connectors that match your battery.

Spektrum SMART Series Harness: IC5 Battery with 4" Wires, 10 AWG | Horizon Hobby

The Series Harness: IC5 Battery with 4" Wires, 10 AWG by Spektrum SMART is a quality built accessory. See all our remote controlled accessories online at Horizon Hobby!

www.horizonhobby.com

 

[steverebo]

Yes it’s possible. You need to make or buy a series harness with connectors that match your battery.

Spektrum SMART Series Harness: IC5 Battery with 4" Wires, 10 AWG | Horizon Hobby

The Series Harness: IC5 Battery with 4" Wires, 10 AWG by Spektrum SMART is a quality built accessory. See all our remote controlled accessories online at Horizon Hobby!

www.horizonhobby.com

Thank you, are there any guides on how to do this?

 

[E-HP]

Thank you, are there any guides on how to do this?

Here’s a YouTube video on the basics, but depends on your battery setup. If you have a Hailong pack, you’d need to adapt, but still the same thing conceptually.

 

[calab]

Series adapter from hobbyking uses XT60's and 12?awg, hobbyking sells XT60's with wire already soldered to the XT's that you could just solder the wires the way you want. They sell series adapter in a couple different flavors, connector based (does not use any wires) and wire based (uses wire) to make the adapter. Series and parallel, series for the extra voltage (for more rpm) and parallel for the extra Wh or Ah to get more distance.

If making one yourself using XT's connectors and soldering wire on then use the copper bowl cover that clicks in, I like install a bit of heat shrink over the bowl as far down as you can get (to protect it), and lots of heat shrink on the wire side, I try to keep the heat shrink even lengths (for looks) but I dont try all that hard just make sure the bowl is covered with no wire showing (stripped too much insulation or cut to small a pc of heat shrink)

I wouldnt use any of their other connectors, only the big bullet connectors 4mm or bigger. I find soldering the big connectors easier, but if your doing it yourself, pay attention to heat management as you will melt the housing if your not careful. A pc can or air is helpful to cool things down but dont shock the solder. A small fan blowing on the connector will help cool it down. Generic irons the 40w is good, but I like the 60w generics from Harbor Freight.

I have a couple techniques I use. I touch the inside of the bowl to heat it up, move iron to the outside of the bowl while solder is being applied into the bowl.

Make sure the connector wont move, I like locking pliers and the XT sits in the curved section of the grip real good. They do sell adapters to hold connectors but dont waste your money. For bullets I drill holes in wood to hold the 4mm or bigger bullets.

One connection is fine, but as soon as you have to start unplugging multiple adapters (like Lipo bricks) every charge, mistakes happen when your tired after a day of riding, when you dont have much light, dark or your rushed.

One little "Ooops I connected it the wrong way" and you'll see why! Just hope you dont have to buy a new cheap generic or expensive controller or new battery.

 

[steverebo]

So it's as simple as plugging the extra battery into a series Harness and setting my voltage to 48v?

 

[calab]

Match the parallel batteries

I dont know about series. For example in a series connection (absolutely dont do this in parallel) if you had 36v 10ah 360wh and a 12v 1ah (12wh) battery in series to make 48v then would one drain quicker?

 

[E-HP]

So it's as simple as plugging the extra battery into a series Harness and setting my voltage to 48v?

Since your packs have different capacities, you will have to monitor them (mostly the smaller Ah pack), to make sure you don't over discharge them.

 

[Hillhater]

What chemistry is your 36v pack ?
does it have a BMS ?
what is the max current draw from your controller ?
what is the rated max discharge of the LiFePo4 pack ?
what will you use to recharge this 36/48v pack ?
If you do not fully understand the implications of what you are planning to do,..you are flirting with risk of a battery melt down or fire.

 

[steverebo]

Since your packs have different capacities, you will have to monitor them (mostly the smaller Ah pack), to make sure you don't over discharge them.

I'm using lifepo4 8ah as ny second specs are:

Battery Type:	Lithium Iron Phosphate(LiFePO4)
Cycle Life:	4000+
Voltage Range:	9.5-14.6V
Nominal Voltage:	12.8V
Capacity:	8000mAh
Wattage:	102.4WH
Max Charge Current:	7.5A
Max Discharge Current:	10A

My main battery is a 10.4ah 36v lithium ion battery. Both have bms and I will charge them with thier own chargers

 

[E-HP]

I'm using lifepo4 8ah as ny second specs are:

Battery Type:	Lithium Iron Phosphate(LiFePO4)
Cycle Life:	4000+
Voltage Range:	9.5-14.6V
Nominal Voltage:	12.8V
Capacity:	8000mAh
Wattage:	102.4WH
Max Charge Current:	7.5A
Max Discharge Current:	10A

My main battery is a 10.4ah 36v lithium ion battery. Both have bms and I will charge them with thier own chargers

Charging separately works, but you should have at least one voltmeter monitoring the smaller pack voltage, and preferably one on the other pack too when discharging.

 

[docw009]

I've done this in the past, putting a 36V and 12V batteries in series. Each had their own BMS and I would take them apart for charging separately. Either battery would shut off via its BMS if they dropped to their respective minimums, but this never happened because I never ran the combo much past 50%.

One thing I did not realize at the time is the risk of battery damage if either of the batteries is shut off by its BMS. If one of the BMS circuits shuts off, its output transistor will see the entire voltage from both batteries. Those transistors must be able to withstand the voltage. In the case of a 36V and a 12V battery in series, the max voltage is 54 volts, while a typical voltage that might happen if one battery happened to shutdown would be around 40V volts of both batteries drain evenly.

Here's a picture of the BMS in my 12V battery. Just a nice little 3S BMS for li-ion cells. It was my first battery that I built. It was ugly, because I soldered 12 Li-ion cells together to make it.


Take a close look at the power MOSFET's. There are FDD6030L's. These are only rated for 30V maximum, There is a real risk that they could be damaged by a nominal 40V.



If they blow up, the worst is if they short circuit, which would keep my 12V BMS always turned on. Then I lose the BMS protection, which is dangerous.

For me, nothing happened. I never had either battery shutoff. But it's happened to other people, although they had higher voltages, and one guy posted here about a fire. And now that I know about the issues, I don't put batteries with BMS in series .

I just want to add a little science to the discussion. I doubt there are many 12V batteries with BMS transistors rated for 50+ volts. That would suggest that series arrangements have some risk of battery damage, which means a risk of fire.

There are ways of avoiding this, but other guys can tell you about them.

 

[steverebo]

So if I attach a voltmeter to the booster battery I can keep an eye on the charge level of just that battery even though its in series?

If that's the case my main battery already has a button I can press to check charge level and my only concern should be the booster battery which has the slightly lower ah level. So if I put a voltmeter on it I can Check before my commute each time what the charge level is.

Is it safe to store the battery in a small pannier bag at the rear of the bike directly above the main battery?