Using 48 V 14Ah battery offline for power to Convertor

[sunnymike]

I am trying to use the bike battery off-line to power a trolling motor for my kayak. It is from my RadCity bike 48V 14 Ah. I can connect to the power output and get a 53V output when the key is on. When I connect the battery to the convertor input this voltage drops to zero at the convertor. This of course doesn't happen when the battery is on the bike. Are the 3 smaller connections on the battery used to control the batteries power on and off?

[SQFRad]

You should check out this video of someone doing something similar https://youtu.be/vP13pjChTB4?si=IbGcigNGjZATX8BI

[sunnymike]

Thank you.

I did check this out. He had the same problem I do on an older battery of the same size. He did purchase a spare battery and it is different. The power stays HIGH when he hooks the new battery to his convertor. I would rather understand why the older battery goes LOW when a load is applied so I can use it to power my trolling motor when kayaking. It is 24 Vdc. So, 2 new high Amphour batteries would be very expensive.

[SQFRad]

Sounds like a neat project in any case. Was your battery part number the same as his older one?
I'm also curious, do the three pins on the battery connect to anything on the bike?

[sunnymike]

Yes his older one matched my part number.

[DickB]

I would guess that the BMS in the older battery is shutting the battery down because of excess current draw or unbalanced cells. Try test connecting a lesser load, such as several automotive batteries in series.

The three smaller pins are not connected to anything.

How are you connecting these batteries in parallel? This is potentially problematic.

[sunnymike]

Thanks for the reply,

The batteries shutdown without any load on the output of the converter.

I have leads from the neg. and pos output on each battery. I then connect both neg leads to the common lug on the convertor and both pos leads to the pos lug on the converter. It doesn't matter if I connect one or both batteries, they shut down in both cases.

I am a little surprised that the 3 little connectors go nowhere. There are 3 little pins in those spots on the connector. I was betting they were for that 3 button switch on the handlebar that turns the power on, selects the PAS setting and other switching functions. Oh, well. That's why I am asking you for help because guessing just gets me into a lot of trouble.

[DickB]

Thanks for the reply,

The batteries shutdown without any load on the output of the converter.

I have leads from the neg. and pos output on each battery. I then connect both neg leads to the common lug on the convertor and both pos leads to the pos lug on the converter. It doesn't matter if I connect one or both batteries, they shut down in both cases.

I am a little surprised that the 3 little connectors go nowhere. There are 3 little pins in those spots on the connector. I was betting they were for that 3 button switch on the handlebar that turns the power on, selects the PAS setting and other switching functions. Oh, well. That's why I am asking you for help because guessing just gets me into a lot of trouble.

You may be getting a current spike into the converter even if the converter is not connected to a load. Hard to determine without an oscilloscope.

Connecting batteries in parallel as you described is problematic if the batteries are not at the same charge voltage. The batteries can be charged through the load connection, as happens with a regen bike. If the voltages are different, you're going to get current flow from one battery to the next which, depending on the difference, could be a sizable current. You should be using a Datex2 or similar device.

Do you have any specs on the current draw of the converter and of the trolling motor? Or at least pounds of thrust specs? You may be asking too much of the bike batteries. With inefficiency of the converter I suspect that you're not going to get a lot of run time with the bike batteries. I need some info on the converter and trolling motor.

[sunnymike]

Thanks again,

The 2 batteries were recently fully charged. One was at 53.7Vdc the other at 53.8Vdc. Also remember I hooked only 1 battery to the convertor and it still went to zero volts.

I have 2 matched 22.2Vdc 4Ah Heavy Duty r/c batteries I am going to try with them in series.. I need to get some connectors first.

The trolling motor has 86lbs of thrust is 24Vdc Has 5 forward and 3 reverse speeds, it draws 48Amp max.
So that's about 1200 watts and the 2 batteries in parallel are about 1300 watts capable.

The converter
Specifications:
Input Rated Voltage: 48V DC
Input Voltage Range: 30-60V DC
Output voltage: DC 24V 60A
Output Rated Power: 1440W
Efficiency: 97% (half load); 95% (full load)
Ripple: 200mVp
Line Regulation: ±0.2%
Load Regulation: ±0.2%
Voltage Accuracy: ±1.5%
Enclosures: IP68
Case Operating Temperature: -40~85°C
Weight: 2200g
There is an external resettable 50 amp circuit breaker supplied on the output of the converter

I will buy a Datex2 as suggested is a 60Amp rating on that good enough?

Also I do have a Tektronix Oscilloscope I haven't used in 15 years. I know I have a set of probes still hanging on the wall. I hope I can find the manual. I'll give that a try to see if I can see a current spike.

Thanks again for the help.

[sunnymike]

I connected 2 22.2Vac 4Ah batteries in series giving me 46.3Vac at full charge. Hooked the trolling motor up to the converter output. Plugged the batteries into the input of the converter. Voila it worked. Rather than try to make the Rad Power batteries work I ordered 2 new 48Vac 16Ah LiPo batteries from EBay which have a BMS and charger but only 2 power leads to an XT60 connector. Hopefully they work OTB like new Rad Power batteries would and come with a circuit diagram for the BMS. Wish me luck.