switching to a new 4 prong battery from 2 prong?

Hello,

I need an answer ASAP. I am attempting to switch to a "new 4 prong battery" from "2 prong battery."
The old battery is a "silverfish" design that is vertical just behind the seat tube, 36V 10ah with a positive and negative female connector. A friend wants to sell me a "new" battery of identical volts/amphr specifications, EXCEPT this battery has 2 positive and 2 negative female connectors.

My question is that is it OKAY to just use 2 of the 4 connectors? Will this allow enough amperage to supply the bike? It only a 250w motor. I just don't want to damage the "new" battery by perhaps only pulling current from 2 of the 4 connectors.
Please any feedback would be appreciated.

Thanks,
C

It depends on the connector, it's capacity, and the system power.

It will probably be ok with a 250w motor, but most 250w motors aren't actually 250w.

my real concern was that BOTH positives were needed, and BOTH negatives needed, instead of just the 2 on the bike controller. Thinking that maybe each of the positive slots and each of the negative slots, would drop the battery capacity to half by only utilizing 2 instead 4.

Anyone know what I am asking?

Just FYI I am getting full battery voltage (42) when measuring a pair (+ and - ) of only 2 slots.


I just do NOT want to only discharge half of the battery by only using 2 of the 4 slots...

I've never seen a pack wired as you fear, only in parallel.

Most likely a BMS with "separate port" design, so charging can be cut off independently of discharging.

One side may be protected against overcurrent by the internal BMS, while the other side bypasses that function to allow higher rates.

Two ways to know for sure

break open the pack and look at the BMS and how it's wired

put it through some cycle testing with an ammeter

More connectors are usually put for better power transfer. Load better spread = lower temperature.

Both sides of the connector have to have 4 for it to matter. So 4 on one side + 2 on the other = 2 connectors.


In short, NOTHING CHANGES.

Tommm said:

More connectors are usually put for better power transfer. Load better spread = lower temperature.

Both sides of the connector have to have 4 for it to matter. So 4 on one side + 2 on the other = 2 connectors.


In short, NOTHING CHANGES.

Click to expand...

Thank you that makes perfect sense. Since this 36v battery came from a 400w bike, and is now being out onto my 250w "townie" I will sleep a little better. However the previous owner had a dullard do the last battery swap and just flattened a positive and negative spade connector and jammed it into the existing battery. So in turn I took the "new" battery with 4 slots, and used my two wires into 2 of the 4 ports. I had thought to further reduce the chance of any of the considerations mentioned in previous replies to this thread to make my own parallel harness and utilize all 4 ports... However, I will take it out for a short 6 mile ride tomorrow, and then measure the voltage on each pair of the 4 ports, and report my findings here (instead of opening the battery). I hope this will give me a more concrete answer, or I will build the parallel connector before my ride. Either way I will report back on this thread.

Thank y'all for all of your timely feedback, and I hope to be able to contribute answers when I have knowledge to do so definitively.
C

Are you sure you're not talking about two wires for discharging (to the controller), and two other wires for charging (charging through the BMS)?

E-HP said:

Are you sure you're not talking about two wires for discharging (to the controller), and two other wires for charging (charging through the BMS)?

Click to expand...

No I am not sure. The battery just has + + - - whereas my old battery just has + -

They both show full battery voltage. The "new" battery did come off a 400W bike, and is being installed onto my 250W prodecotech "townie."

I am going for a 6 mile short ride later today and will check voltage and temperature of those conductors and report my findings here in this thread.
I am only hesitant to open up the battery because my friend is just letting me borrow it for now to see if it will work for my bike. once I own it I may very well do that and post photos here, just in case other people encounter the same question.
Thanks.

I have a bike with one of those silly silver fish packs. Mine has space for four terminals but only populates two,and the socket on the bike only has two terminals. I'm running it with a 20A 36V controller. It came with a 17A controller. So it's two prongs and 500-600 watts.

Nothing to worry about, in my opinion, although four prongs would be better for maintaining contact. The pack, as you know, just sits on the socket with no allowance for the contacts getting loose. In fact, mine would rattle, so I put some rubber padding between the battery base and frame. Also strapped it with an elastic strap.

docw009 said:

I have a bike with one of those silly silver fish packs. Mine has space for four terminals but only populates two,and the socket on the bike only has two terminals. I'm running it with a 20A 36V controller. It came with a 17A controller. So it's two prongs and 500-600 watts.

Nothing to worry about, in my opinion, although four prongs would be better for maintaining contact. The pack, as you know, just sits on the socket with no allowance for the contacts getting loose. In fact, mine would rattle, so I put some rubber padding between the battery base and frame. Also strapped it with an elastic strap.

Click to expand...

Thanks. I missed my ride today so I will try again tomorrow.
Also photos.

E-HP said:

Are you sure you're not talking about two wires for discharging (to the controller), and two other wires for charging (charging through the BMS)?

Click to expand...

Hello, Thanks for your reply and query. I just tested the "new" battery on a 20 mile PAS ride. When I detached the battery I was only able to measure any voltage on the "outer" + and - slots... as shown here.


The "inner" + and - slots read zero volts. Any Idea what they may be for? Just the extra stabilization of 4 prongs?

Hello here are the photos I promised.

The first is my old battery.

This is my new battery. The only terminals I read any voltage on have probe wires inserted.

The ride with the new battery was 20 miles. Pretty flat Florida terrain. Pedaling but full throttle and PAS. The simple battery display on my ebike only has 5 red LED's . When I got home from the ride, the display showed only 2 LED's and the battery volatge had dropped from 42 down to 35.5 according to my volt meter.

The bike is a Prodecotech "Road King 2500" 36volt 250watt motor. I made the saddlebags myself. They are plastic, waterproof (O-ring), and lockable. They weigh less than 2lbs each.

Am I crazy, I'm in the same boat as you OP. But according to your photos, these batteries are opposite polarities. How is this possible?? In your old battery photo, with the rail section facing down. Negative is on the right side. Then on your new battery photo, if you place the battery the same way as the old one, with the rail section down. Negative would be on the left side. What am I missing here??

The photos should be placed like this:

Maybe he flipped the second picture left-to-right. On my Silverfish pack, the terminals are like the top picture you showed with the "+ S -". In other words the positive terminal is nearest the drive chain.

I only have the one pack, but it only uses the two outer positions.

docw009 said:

Maybe he flipped the second picture left-to-right. On my Silverfish pack, the terminals are like the top picture you showed with the "+ S -". In other words the positive terminal is nearest the drive chain.

I only have the one pack, but it only uses the two outer positions.

Click to expand...

True, he might have, but if so he should have been clear. Someone with the same problem might see his post of success and think using the opposite polarities is fine, as I almost did -_-. Maybe OP can clear it up.

For those who have an issue about polarity. Be vary careful and make sure the battery is off, and probably wear rubber gloves for safety. You can open the bottom of the battery (taking out 4 screws). Then there are 2 more screws holding the terminal case to the bottom, these might be covered by glue or foam padding. Then there is one finals screw which you can remove which lets you move around the ports themselves.

docw009 said:

Maybe he flipped the second picture left-to-right. On my Silverfish pack, the terminals are like the top picture you showed with the "+ S -". In other words the positive terminal is nearest the drive chain.

I only have the one pack, but it only uses the two outer positions.

Click to expand...

Here is a better photo. Yes the previous photos were not rotated and shown side by side. Here you are:



You should be able to tell that the polarity is opposite. Not shown is also the charging port and key switch are on the opposite side than my original battery.

I made it work, and did a 20 mile PAS ride and came back home with 3 out of 5 "bars." These bike have a very simple battery display, just a series of 5 LED on the handlebar display. They also have a minature display on the battery itself, but has even fewer levels.