Feb 21

Pino update

Adding a second battery

The International Tandem Rally in 2022 in the first week in August, was near Tecklenburg, South West of Osnabrück in Germany. We thought it would be good to ride from home, using the Stena Line Ferry from Harwich to the Hook of Holland. Once in the Netherlands the going would be mostly flat but between us and Harwich and in Germany there would be a fair amount of climbing.

The route from home to Harwich (North leg) and the return route (Southern leg), planned to collect BCQs along the way.
Hook of Holland near Rotterdam and the International Tandem Rally site near Osnabrück.

At the time, the 17.5Ah battery fitted to the Pino was good for around 30 miles with reasonable use on the unloaded tandem, but I was a bit anxious that hauling the loaded bike and trailer would reduce the range as the motor would be needed more, especially in hilly terrain. With this in mind I looked at either obtaining a second ‘reserve’ battery or another to add to the bike.

The type of connector in the mounting bracket on the current 36 volt 17.5Ah (630Wh) battery, then 3 years old, which I bought from China has been changed and I thought it unlikely to be able to buy a second identical ‘spare’ to match the existing bracket, so I looked at connecting a second battery.

The logical choice was a rack mounted battery. I wanted a system that would allow me to use just one or both. Two batteries for a shortish local ride would be overkill and unnecessary weight. However, on a longer ride, in much hillier terrain or on a fully loaded tour, the ability to have both batteries providing power would drastically increase our range. An advantage to using both batteries at the same time rather than one then the other, is that at maximum draw by the motor, each battery is only providing 50% of the power, so the batteries are not stressed nearly as much as a single battery providing all the power.

Looking for more information on the web, I came across ‘Area 13 e-bikes‘ and some useful videos on battery care and how to add a second battery to an e-bike. With the advice from this video I ordered the Dual Battery Parallel Connector. This would allow me to safely use the two 36 volt batteries of different capacity on the same system, or either battery individually. Something similar is available in the UK, but costs a lot more. Delivery from the ‘States took a little over a week. I ordered some XT90 connectors to match the ones on the Dual Battery Parallel Connector. Because the original battery did not have an isolating switch, I also bought an inline on/off switch so I could isolate the exposed connector on the down-tube battery bracket when we were using the bike without that battery fitted. Without the switch I am pretty sure the connector would be live and very prone to shorting out if it got wet.

The Dual Battery Parallel Connector with XT90 connectors, bought from Area 13 e-bikes in the USA. Something similar is available from UK suppliers, but at double the cost. Even with shipping, the US type I bought was way cheaper.
My soldering left a lot to be desired and after losing power on a ride, due to a loose connection I swapped out the XT connectors for a more basic type above. The connections are protected with self amalgamating tape.
The original down-tube mounted battery and bracket, showing the exposed connector which would be live without an isolating switch if we were just using the rack-mounted battery.
The finished set-up, as it is in September 2023.
The end result… The Pino with the original down-tube mounted was 17.5Ah battery but after 4 years its performance was no longer acceptable, so I recently replaced it with a 13Ah in the same size casing. The new tube-mounted battery has an on/off switch and recessed connections. Both batteries now provide a total of 35.5Ah or 1278Wh which is enough for a day ride with a touring load.
Just visible at the top, behind the seat tube is the waterproof rocker switch which allows me to isolate the down-tube battery bracket. The rack battery has a switch and USB outlet, plus a rear light.
A rather distorted view. The Dual Battery Parallel Connector is tucked between the rack struts and rear mudguard, covered with some old inner tube which I cut along and opened out. It works a bit like extra wide bar-tape and is held fast with some velcro.

The beauty of this system is that either both batteries or just one can be used, without the other being on the bike. The large capacity rack mount battery weighs 5.8kg (12.7lb) and the down-tube battery weighs 3.5kg (7.7lb).