Bolton Ebikes Dual Battery Parallel Connector causing random sudden over volting?

[zeddrick]

Bolton Ebikes are selling a Dual Battery Parallel connector rated for 30a current, my ebike has a 30a controller and I have two 48v batteries that I'd love to put in parallel so I wouldn't have to manually swap batteries all the time. They say the connector has smart features that will save your batteries from damage if you were to connect them in parallel with different levels of charge, that it would only drain from the higher charged battery first until it reached the same charge level of the other battery and then it would use both at once.

I was wondering how charging would work with it once connected though. Would I just charge one battery now? Could I charge both at once for faster charging or would that be dangerous? Once the two batteries become one through the parallel connector I would assume I would just need to charge one right?

 

[john61ct]

Dunno but Wattwagons used to sell a dual-battery "converter" struck me maybe the same

 

[ben2401]

Bolton Ebikes are selling a Dual Battery Parallel connector rated for 30a current, my ebike has a 30a controller and I have two 48v batteries that I'd love to put in parallel so I wouldn't have to manually swap batteries all the time. They say the connector has smart features that will save your batteries from damage if you were to connect them in parallel with different levels of charge, that it would only drain from the higher charged battery first until it reached the same charge level of the other battery and then it would use both at once.

I was wondering how charging would work with it once connected though. Would I just charge one battery now? Could I charge both at once for faster charging or would that be dangerous? Once the two batteries become one through the parallel connector I would assume I would just need to charge one right?

I’ve been running two 13s3p batteries in parallel for two years and hundreds of charge cycles by now. You only have to plug the charger into one. I leave them connected with no issues and both charge. My batteries have a separate charge connector on each along with the XT90 connectors. I leave the two batteries hooked up to the parallel XT90 harness I made and plug the charger into one of the small “laptop-style” connectors. I only charge at 2A. If you want to charge at much more than that (since the thin wires can only handle that much) you will have to charge through the main power connector which means disconnecting it every time.

 

[fechter]

It will depend on how the BMS for each pack is configured. If the BMS boards are "two port" style, then charging them connected may not give overcharge protection to the second pack. If they are the "single port" style, then just charging one will charge both at the same time safely. A single port style will only have one pair of wires coming out of the pack and both charge and discharge go through this pair. Dual port will have a separate pair for charging and discharging. For dual port, the safe way to charge both would be to separate the packs from each other and charge each pack separately (or use two chargers). The "smart" parallel connector may change things but without knowing how it's designed you may need to test a little to figure out how it works.

 

[zeddrick]

Ever since using this Bolton parallel connector to put my two 48v batteries in parallel I have been getting random split second over volting when climbing some steep hills (a sudden split second acceleration with my display showing 65 to 70+ voltage for a second and then going back down to a normal voltage for my batts, 54v being the max my voltage should be). It must have something to do with the parallel "smart" connector because I tested each battery independently today without the parallel connector and there was no over volting at all.

When the parallel connector causes a short sudden over volt It feels like it happens most when I'm reaching the peak of the hill when it starts to become less steep and flatten out, I naturally let off on the throttle a little and then the power slingshots up beyond what it should for half a second while the voltage reads something like 72 for a split second, and then it returns to normal. But it has also done the same thing when the gradient is unchanged and the throttle is consistent at 100%.

I've messaged Bolton Ebikes about this but I'm waiting for a response. There's a lot of really smart ebike people in here so I figured I'd ask here too. My ebike is from an Ebikeling 48v 1200w DD rear wheel kit, controller is stock and rated for 30a, voltage settings are default and safe in S830 display, both batteries are 48v20ah (one LG rear rack, one UPP triangle, I believe both are rated for 30a continuous but the UPP I think has a "max" discharge of 50a while the LG says "max" discharge of 40a).

 

[E-HP]

What is your charging routine?

 

[zeddrick]

What is your charging routine?

I turn off the bike and I use the wall chargers that each battery originally came with, charging at the same time. I've read that some people charge through the xt60/xt90 battery cables? I don't do that, I just use the generic wall charger that each battery came with, and I don't mix them up because they have different style ends. I charge them at the same time to keep the voltages closer together at the start so the "smart" feature of the parallel connector doesn't have to drain from the higher voltage one first for very long before they are both being drained equally.

Also a thing I just realized is that when I first got the parallel connector everything was fine for a week straight when I started off using the batteries from 54v charge down to around 51v charge, but the first over volt the other day was when my batteries were at around 50v or less.

 

[E-HP]

Trying to think of what conditions could cause a spike. For instance, if one battery was 2 or 3 volts higher than the other, then that would provide all of the power, but as you start going up the hill, the voltage will start to sag under load, and at some point the second battery kicks in. Normally it wouldn't, but the sag makes it happen. When you crest the hill, the load drops, and the lower voltage battery drops off. Maybe the display is reacting to spikes, and not necessarily reading the voltage? Seems like it could be connected to the switch over.

 

[zeddrick]

Trying to think of what conditions could cause a spike. For instance, if one battery was 2 or 3 volts higher than the other, then that would provide all of the power, but as you start going up the hill, the voltage will start to sag under load, and at some point the second battery kicks in. Normally it wouldn't, but the sag makes it happen. When you crest the hill, the load drops, and the lower voltage battery drops off. Maybe the display is reacting to spikes, and not necessarily reading the voltage? Seems like it could be connected to the switch over.

The only thing that really concerns me is the split second surge in power that happens, I can feel it kick in for sure regardless of what the display might be saying, it's slight and very very short but it's like someone pushed me forward for a split second. The first time it happened it did it two times in a row; like I felt a power surge push me forward like a quick jolt and then 5 seconds later another power surge, then I pulled over and turned the bike off.

I think you're right (if I understand correctly) that it happens when it isn't draining from both equally at the same time, but the reason I bought this "smart" parallel connector was because it's supposed to prevent stuff like this from happening even if both batteries are at vastly different levels of charge.

 

[E-HP]

but the reason I bought this "smart" parallel connector was because it's supposed to prevent stuff like this from happening even if both batteries are at vastly different levels of charge.

I can see them claiming it wouldn't cause it from happening, but probably not prevent it. I'm guessing the primary benefit is to prevent accidentally frying the batteries when one is charged more than the other when you connect them. Otherwise, a straight parallel cable would make things more seamless under use, and not introduce another problem. Basically a trade off, seamless under use vs safer if you accidentally skip a step.

 

[zeddrick]

So do you think the random power surges are doing any lasting harm to the batteries, controller, or motor? If it's just a weird harmless quirk of the parallel connector that isn't effecting anything else negatively then I'd be fine with it.

 

[Klauts]

You still alive?

 

[lnanek]

Not sure why thread is being resurrected, but worth pointing out I had similar issues with a battery combiner until I turned off regen on my controller. Some of them don't support that.

 

[ZeroEm]

by lnanek » Jan 21 2023 5:48am

Not sure why thread is being resurrected, but worth pointing out I had similar issues with a battery combiner until I turned off regen on my controller. Some of them don't support that.

Was wondering how he was getting 72v, regen makes sense. Wondered if his controller was a 60v max and how it could handle 72v. Lots of questions, few answers.

 

[amberwolf]

A battery combiner using diodes to isolate the batteries from each other cannot support regen, because the diodes also isolate the batteries from the controller's regen.

So when you engage regen, or the motor speed (like downhill) exceeds the drive from the controller so it generates a higher voltage than the battery voltage, there's no load on that so it just spikes inside the controller, and can destroy the controller FETs and LVPS, at minimum, if it exceeds their ratings.


If the battery combiner uses FETs or physical switches to connect the batteries to the controller at the same time, and does not isolate them from each other, then it also doesn't isolate them from the controller, and regen would work with them essentially as if the batteries were directly connected.