Gold Bullet Connectors - Which size for 18S? 4, 5.5, 6, 8mm?

ryan

ryan

10 kW
Joined
Dec 3, 2009
Messages
638
Location
California Bay Area
I'm planning a 18S4P pack with 6S1P 8Ah 30C Zippy LiPos. They come with 5.5mm bullets, but is that enough? I also have a hundred or so 4mm connectors laying around.

HobbyKing lists their ratings accordingly:
4 = 93A
5.5 = 100A+ (I can't find anything more specific)
6 = 120A
8 = 170A

I like the 4mm bullets because the protector housings are pretty foolproof. Like Andersons, they're pretty difficult to short them out because it's impossible to put them in backwards. The others don't come with housings.

What is the equation to guide me here?
 
The voltage of the pack means little as to what connects you should run. There's terrible connectors out there, but the bullet HXT's are OK. You should be fine running anything from 4mm on up.

The 4mm's get hot enough at 90A to melt the solder, and there is going to be essentially no mechanical connection to hold the wire once that solder melts. For brief periods, they will do 90A+ no problem. If you plan on running them at something like 80A for a several minutes to hours, look at something a bit bigger.

All you really need to worry about is what size wire you want to run, make sure it fits into the connectors. As long as your continuous current is 1/2 of the max current rating of the connector, it will be fine.
 
Stick to the stock connectors unless you're gonna go crazy and draw over a hundred amps.

My 4mm bullets stand up to frequent constant 55-57a discharge, 5.5mm would of course have less resistance.
 
Take a look at Icecube57's harnesses. In forsale new. Even if you build your own he has some nice ideas, and he will do custom if you need something special.

I'm using bullets at the battery, whatever is supplied, and then paralleling/seriesing with PowerPole 75's. Dual connectors are either PP75 or SB50, varying the connector so things don't plug together wrong.
 
How do you cover these larger bullets? Just heat shrink? That seems too permanent. Is that the purpose? That once these bullets are connected, they stay that way?

I saw AussieJester's YouTube video on soldering the bullets. I can do that just fine. But what about covering them? Protecting from KFF?

Do they make larger plastic housings like the 4mm ones? Those are great.
 
Or, is it worth upgrading to 6mm XT50s? Rated to 250A.

XT150.jpg
 
So many choices.

Requirements:

shrouded for safety
not able to plug in wrong, or at least color coded for correct setup
carry current without heating
not too hard or too easy to plug and unplug
handle wire sizes
fit batteries without changing battery connectors
easy to install

here's my plan:

LiPo%2525203P%252520cable%252520section%252520V1a.jpg


The basic idea is to use the connectors to parallel the wires so I don't need more connections. This is a 3P plus a balance charging connector so four wires coming into the connector. Since the connector is a PowerPole 75, and it will take 6 gauge, I can bring in four 12 gauge wires to the one connector. PowerPole 75's have a few colors of bodies so I can snap color coded covers on them. It doesn't prevent mating wrong but makes it easy to tell. I'm not going to be taking them off for charging so they don't have to be handled often.

In my case the batteries take 4mm bullets in shielded connectors, but whatever the battery has is what I'll use. Minimize changing connectors. Minimize connections. Parallel first, then series. With a 2P setup I would probably go to 10 gauge for the batteries and 12 or 14 gauge for the charge line, so it would fit together in #6.
 
I really don't think anyone here is going to have issues running 4mm bullets.

Ok I take that back. You can't as easily use 8 awg or 10 awg wire in them. Which means you'll be looking at some bigger resistive power losses in your cabling. But I don't think 4mm bullets are gonna melt first in a hub motor setup. I mean 90a? Your hub motor is gonna melt first.

I bought 50 pairs of 4mm bullet connects on ebay for like $20. Great deal.

The 4mm bullets between the parallel groups of batteries see 55a continuous and don't get warm at all.

Then I use 8mm bullets for phases, and main battery connections. This is mostly so I can use 8 awg cables.

The difference in power losses between 8awg and 12awg is between 30 watts and 140 watts.That's a huge loss of power. And most wiring harnesses are 14 awg. Honestly, you wanna know the secret to eeking out the most performance from your ebike? Upgrade your damn battery and phase harnesses.
 
auraslip said:
The 4mm's get hot enough at 90A to melt the solder,
Click to expand...

REALLY?
Click to expand...

The ones I got from HK can. The wire wicks away the heat for a while. With very short wires, very high currents, or a long period of time, the 4MM HXT's fail before the wire does. At least, the ones I used. They're probably made out of some semi-conductive super cheap Chinese metal. They were quite inexpensive. The gold plating probably makes up a significant portion of the cost.

They never get remotely warm on my bike, but when the limits are tested, 93A is a bit questionable for a continuous rating.

That said, the 4MM HXT's are a good connector for most. They are quite cheap as well. One major downside is it's possible to make improper connections with them, and they can not be 'reversed'. If you had HXT's on something like a Watts Up, the meter could not be reversed to measure charge current, unless you like reverse polarity. Thats the major reason why I only use them to interface to a battery equipped with them stock. Everything else tends to be PP's.
 
From what I've seen, the 4 mm bullets are actually bananna plugs. That is to say, the contact area is not the entire barrel on the male side. It's just the 4 springs on the male side that actually contact.

So if you are pulling serious juice, get the 5.5 mm. Cover em with heat shrink and then if you want better protection, find some plastic tubing that fits over the bullets. Or just multiple layers of shrink.
 
dogman said:
From what I've seen, the 4 mm bullets are actually bananna plugs. That is to say, the contact area is not the entire barrel on the male side. It's just the 4 springs on the male side that actually contact.

So if you are pulling serious juice, get the 5.5 mm. Cover em with heat shrink and then if you want better protection, find some plastic tubing that fits over the bullets. Or just multiple layers of shrink.
Click to expand...

Yep. All of the current needs to flow through the thin little spring, before it gets into the body of the connector. At the end of the day, a few of those won't make any noticeable impact on anything <40A or so. Especially if the thing is wired up with 12 gauge or thinner, then the wire would add far more resistance than the connectors.

I've never had any real problems with 10 gauge on my harness. I used the 4mm HXT's to plug into Turnigy packs, and then 45A PP's elsewhere. The wire is fairly thin, and not terribly expensive. It's just a lot easier to run the thickest wire you can get into the connectors and forget about it. The cost, weight, and time difference between using 12 and 10 gauge is minimal. I have heard of some people having issues with 10 gauge fitting into 4mm HXT's, but the HK ones worked fine for me.
 
Out of curiosity how many amps should I expect to use? In my 72v20Ah 10C Headway pack with a Crystalyte 5304 and 5305 I only saw peak Amps up to around 40, when pulling up a steep hill at full throttle, with a trailer.

How will/should this change with a 18S4P setup and a 5404?
 
ryan said:
Out of curiosity how many amps should I expect to use? In my 72v20Ah 10C Headway pack with a Crystalyte 5304 and 5305 I only saw peak Amps up to around 40, when pulling up a steep hill at full throttle, with a trailer.

How will/should this change with a 18S4P setup and a 5404?
Click to expand...
Amps shouldn't change at all (or very minimal) using the same controller.
 
The controller limits the current in almost all cases. The motor's limit varies with the speed of the motor, but tends to be very high.

The only real reason why the peak current might go up, is if your old battery was struggling to meet the demands, and you replace it with a battery capable of much more current.
 
I'm a big fan of the HXT60s.... the yellow polarized connectors. I migrated to them for all my charger plugs. They can fit any size wire on them.

But they sometimes are a PITA to unplug. I've tried using a needle nose to bend the plugs in, and filing the outside down with limited success.


What I've been thinking about recently is how to parallel packs easily, cheaply, and with out a lot of messy wires.

4cc13b91a4647_181543b.jpg


I was thinking that for more permanent situations you could install these, and then bolt them together. Actually, it wouldn't be too hard to undo the connection. Keeping them from shorting might be an issue though.
They have the advantage of being inexpensive, easy to work with, readily available. Also, they would take up MUCH less room. You could cut the wires on the packs down very, very short.
 
auraslip said:
Keeping them from shorting might be an issue though.
Click to expand...

You got that right! Whatever you do, make sure you don't have unshrouded positive and negative battery connectors at the same time, no matter how careful you think you are being. :)
 
Grinhill said:
auraslip said:
Keeping them from shorting might be an issue though.
Click to expand...
You got that right! Whatever you do, make sure you don't have unshrouded positive and negative battery connectors at the same time, no matter how careful you think you are being. :)
Click to expand...
Although not as neat as having connectors side-by-side, I usually put them with an offset along the cable, such that they will never have a chance to touch.
 
Dig down to Aussie jesters old thread on his buss bars for a really good method of paralelling a lot of packs.

But you could do a buss bar setup that bolted the connectors. Just have boots to put on them till you bolt up!
 
Normal bullet connectors on battery leads...no wonder people have accidents with their RC lipo packs. Leave the factory leads alone, they're made for the rated current, which you are unlikely to be running.
 
Normal bullet connectors on battery leads...no wonder people have accidents with their RC lipo packs. Leave the factory leads alone, they're made for the rated current, which you are unlikely to be running.
Click to expand...

This is true.

But it destroys one of the main advantages of lipo over lifepo4: volumetric density. Even a 2p pack has enough wires to make a serious mess. Try putting it in a tight space, and you'll see just how messy it can be. For my next build I may just deconstruct the packs and rebuild them as 1s4p. IF I can find a method that works.
 
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