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Old 06-25-2012, 02:10 AM
sabahtom sabahtom is offline
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Default Cell terminal connector - white spots

Just got my terminal connectors made out of galvanised mild steel and tinned copper. Any comments on these white spots? A lot of the connectors have them.
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  #2  
Old 06-25-2012, 06:07 AM
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Default Re: Cell terminal connector - white spots

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Originally Posted by sabahtom View Post
Just got my terminal connectors made out of galvanised mild steel and tinned copper. Any comments on these white spots? A lot of the connectors have them.
Do NOT use connectors made of steel.

edit........Looking again at that photo, it appears that the tab is just crimped on to the braid. This might be acceptable for automotive engine grounding or other 12 volt chassis connections. But in my opinion is totally unacceptable for battery or cell connections on an EV battery pack. Such braided strap connectors for EV batteries are copper all the way, plated with tin or nickel and soldered at the tabs.

Last edited by major; 06-25-2012 at 08:14 AM. Reason: addition
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Old 06-25-2012, 08:34 AM
sabahtom sabahtom is offline
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Default Re: Cell terminal connector - white spots

So they're supposed to be copper the whole way? I'm using stainless steel studs since this is suggested elsewhere on the forum. I see most adverts for LiFePO suggest tinned copper for the terminal and tinned copper braid for the bridge between the terminals. Somehow managed to miss that in my reading.

The reason for not using steel is that even 2mm of it is going to heat up under high current?
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Old 06-25-2012, 08:44 AM
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Default Re: Cell terminal connector - white spots

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Originally Posted by sabahtom View Post
The reason for not using steel is that even 2mm of it is going to heat up under high current?
Among other reasons, yes. Ferrous metal will become magnetized with current flow through it and attract other bits of metal possibly causing a short circuit or ground. And then the whole thing about corrosion
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Old 06-26-2012, 07:23 AM
sabahtom sabahtom is offline
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Default Re: Cell terminal connectors

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Originally Posted by major View Post
Among other reasons, yes. Ferrous metal will become magnetized with current flow through it and attract other bits of metal possibly causing a short circuit or ground. And then the whole thing about corrosion
I ended up with these because I'm a long way from an EV parts shop, and shipping tends to be half the price of anything I buy online. Is it worth taking the steel tabs off and replacing them with copper tabs for welding, suitably rated at 250 amps? My controller is good for 250 rms.

The other possibility is to use the steel tabs for testing at low speed. I'm making a trip to Australia in August so I plan to buy any parts I need at that point.
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Old 06-26-2012, 08:23 AM
swoozle swoozle is offline
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Default Re: Cell terminal connector - white spots

Ya, those look ugly from a corrosion standpoint. You can somewhat easily deal with the exterior exposed surfaces, but the surfaces inside the crimped lug will be a severe problem. And they look to already be rusting.


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Originally Posted by major View Post
Among other reasons, yes. Ferrous metal will become magnetized with current flow through it and attract other bits of metal possibly causing a short circuit or ground. And then the whole thing about corrosion
Seriously, steel becomes significantly permanantly magnetized from current flow? Seems like the permanent magnetic field can't be anywhere as strong as the one created while the current is flowing and I haven't heard that EVs have a problem with that.
I would hope that there aren't enough iron bits flying around to cause a short circuit. If there are, he's got worse problems.
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Old 06-26-2012, 08:24 AM
jeremyjs jeremyjs is offline
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Default Re: Cell terminal connector - white spots

Those steel tabs look like they'd make nice resistive heaters. :/
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Old 06-26-2012, 08:46 AM
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Default Re: Cell terminal connector - white spots

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Originally Posted by swoozle View Post
Seriously, steel becomes significantly permanantly magnetized from current flow? Seems like the permanent magnetic field can't be anywhere as strong as the one created while the current is flowing and I haven't heard that EVs have a problem with that.
I would hope that there aren't enough iron bits flying around to cause a short circuit. If there are, he's got worse problems.
It can happen

Not that EV conversions pay much attention to agency regulations (such as UL), but for battery powered industrial trucks (UL583), ferrous metal is not allowed to be used as a conductor in the power circuit in any form. They don't go into the reasons and perhaps I speculated about the magnetic attraction being a problem. But you can take it or leave it............don't use steel as a conductor in your EV

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