Looking for High Amp, Low Insertion Force DC Power Connector

There are quite a number of options for DC current in this 50-100A range, far too many for me to mention here in fact.

You could try looking at the websites for general component distributors such as RS Components, Newark, etc. You should be able to find something you like and the data sheets are generally available off the distributor websites.

You should also look at their range of solar disconnect plugs and sockets too.

That might be a tough one, but I'd like to add that in some ares such as a airplane DC connector, there exists two pins that get inserted last, thus in a simple form those pins are shorted. Thus the plug is not inserted in a powered condition.

I think the same happens with airplane APU units.

The plastic CPC connectors are relatively easy to insert, but you have to turn a ring which means they won't pass the test.

These guys http://www.multi-contact-usa.com/products/combitac have been advertising here.

So, if you can find one, the charger could provide a current limited say 12/24 V continuous on the receased pins, This would drive a relay in the chair, thus connecting the charger. The chair pins would end up not being live either,

Hearty welcome to CR4.

To make/break the actual power connection, some sort of spring or other high-force mechanism probably has to be involved somewhere.

I don't know if such a device exists commercially, but I am imagining two halves of a contactor that can be positioned with little force, and then actuated by a solenoid with low-level control power. A split relay, so to speak.

You don't actually need a special make and break mechanism in this case as it is unlikely that the connection is going to be made or broken under load (ie- with the power chair DC motor running).

"You don't actually need a special make and break mechanism in this case as it is unlikely that the connection is going to be made or broken under load (ie- with the power chair DC motor running)."

Good point, although if you watch YouTube enough, ANYTHING is possible!

But I don't think the manufacturers of DC rated connectors will manufacture to that issue. In other words their product ratings will assume the worst case.

But I don't think the manufacturers of DC rated connectors will manufacture to that issue. In other words their product ratings will assume the worst case.

I think you will find in general that most are NOT designed for high current DC (or highly inductive AC) breaking, it is just too expensive to design in for standard connectors and in most cases users don't need that load-break disconnection functionality.

_{Jack - Damaged quite a few connectors and contactors switching DC.}

It's a tough problem to be sure. At the heart of the problem is the fact that it is DC. AC power, when you start to disconnect it under load, is crossing the zero-volt line twice per cycle, so on a 60Hz system, 120 times per second. When an arc forms as you pull connectors apart, that arc is much more quickly extinguished by the very nature of AC power. Not so with DC, because it always stays the same. So as you pull apart a DC connector under load, the arc that starts will continue on for a (relatively) long time, which damages the surfaces of the connector. So to compensate, the connectors have longer contact surfaces, and that means more physical force to make and break them.

But there are some connector systems that offer mechanical level operation that may help, call it mechanical advantage. Harting Connectors are the best known and in fact even when made by competitors, people still call them Harting Connectors.

It's a very flexible design system and that means it's also somewhat complex to select, their catalogs can be very confusing at first. But what it boils down to is that you pick the housing style, then the pin inserts you want. But in your case, you almost have to start with the pins, because you need only a few pins of high current rating (Harting is better known for multiple low current pins), and DC, all of which will limit your choices. So my suggestion is to find yourself a good local Harting dealer and work with them.

Good suggestion (if there's one available with a high enough current rating - I've only used them to 10A) - but the latches need quite a lot of force, and are rather fiddly. May be possilbe to modify the latches with longer levers tho'.

Edit - there's a link to 100A contact inserts for then Harting Han Modular range.

Have a look at ECB A or E battery connectors. Which is a European industrial battery connector. Have seen them used on some lift trucks here in the US. They had lower insertion forces then the SB type.

Thanks for the many suggestions, I will certainly be checking them out ASAP.

As further data, a bit more about the circuitry involved -

The way most power-chairs are wired is to use two 12V lead-acid batteries (sealed, gel or AGM types) wired in series for 24VDC, with a breaker in the line between the batteries. The output leads go to the controller (both sides are wired, the frame is NOT used as a ground) that powers the drive motors and other functions of the chair. Part of the wiring is a three pin XLR connector. Two pins are the +/- 24VDC lines, which are connected directly to the batteries, and are always live. The third pin supplies an "inhibit" signal to tell the controller not to let the chair move if the charger is plugged in. The charger is "live" if it is plugged in and turned on, and many users leave it this way and just plug and unplug the unit from the chair...

The modification that we use consists of removing the internal line connecting the batteries in series, and bringing the +/- terminals of each battery out to the side of the chair, to either a pair of Anderson SB-50's or a block of 4 PowerPole-75 connectors. To operate the chair normally, one plugs in an external "link" connector that replaces the internal series connector. Charging can be done with either a 24V charger and line that uses a similar link connector to charge in series, or a 12V source (such as a car, wired with matching connectors) by removing the link and putting the two plugs in parallel. \

Having the plugs on the side also allows the option of plugging in things like 24V power tools, or an inverter to power 110VAC tools without needing to drag extension cords around. If you are willing to temporarily immobilize the chair, you can also drive 12V accessories (It is important to avoid pulling 12V from just one battery as this causes the batteries to be unbalanced, which can cause major problems w/ battery life...)

In addition, some folks are considering switching to the use of a robotics controller and a 45V LiFePO4 lithium battery pack. This would give higher speeds, and either much higher power storage in the same space as the lead acid batteries, or a similar size storage in a much smaller space, and considerable weight savings (on the order of 50%)

Since the plugs on the side of the chair go directly to the batteries, they are ALWAYS live - depending on the power supply the supply lines may also be live. Thus there is always the possibility of doing a "hot plug" connection, with the actual current flow depending on the state of charge of the chair batteries and the difference in voltages between the chair and the connected item...

Since both ends can potentially be live, both ends need some kind of shield or guard to prevent any possible shorting, or contact w/ the chair user or caregiver, etc... The XLR plug does fairly well at this, though you can stick a finger in the end of it. The Andersons are extremely good at this as their design is proof against pretty much anything short of deliberate probing...

Cost is not a total barrier, but it is a consideration (The Andersons are relatively inexpensive, if you shop around they can run $1-2 / pin) This and the limitations on space and so forth would probably rule out the use of any sort of signals to control power supply switching and such that some folks have been suggesting. The simpler approach seems to work well with the Andersons, so I'm hoping that it would be possible to find a lower insertion force alternative that can just be dropped into place...

ART

Have you looked at the RC Communities favourites?

A plug/socket set that comes to mind is the XT60. I have used these and they have low insertion force and excellent low-resistance connection.

You can check them out by searching for XT60 on eBay.

Here's a pic of the sort of setup Art is refering to with the various link configurations for charging or just driving.



It might be worth having a look at the Radsok range

http://www.amphenol-industrial.com/images/catalogs/RADSOK.pdf

Web link http://www.reblingplastics.com/QuickDisconnect.htm

There are a few versions available. they have a worm screw knob which has a low torque value to insert the connector . there is a cover which clips on the battery side when disconnected . Trouble is as they are mill spec they are expensive.

You could try the aircraft surplus stores as these items have a short life in service but are still in good condition.

I used to have some of the battery side connectors taken off old units but unfortunately they have gone out in the scrap.

I was going to suggest you consider using a 4P2T switch with center off to configure the 2 batteries to 12V, 24V or off (disconnected). That way the input/output connection to the chair does not need to be re-cabled for charging or external use and connections don't need to be hot plugged. Still need the 12V lock out to the drive motor and a fuse or breaker (or crowbar circuit) to prevent damage if someone accidentally tries to 24V charge the batteries switched to the 12V configuration.

If you can afford the weight & cost of a 50-100A on board charger, it is sure a more convenient solution, and could still easily give you a 24V external output if desired.

I have seen some electromotive vehicles that would incorporate a lever actuated micro switch with the plug. So that when the two halves mate the switch is closed to make a contactor.That way the connector isn't hot unless some things plugged into it.

Maybe this is 'left field' but two plugs of less fiddly bulk might be worth a look at

link

Did you try calling a local forklift repair shop? They charge (the electric models) every day and may have a good lead on what is easy for insertion.

If it were my jury rigging I would use a L6-30r and plug. Not sure what the insertion and twist resistances are but most I have ever used are pretty easy to turn and lock. I have seen them with special keying so to prevent average mistakes of wrong cord use.

They do make a 50 amp version but I know they are hard to twist and lock.

How about scaling up the multipole jack socket concept? A stereo jack plug has a set of sleeves which make contact with a row of socket contacts. If you wire resistors between each of the socket contacts, and use a single solid probe for the plug, the current on first insertion is limited by the resistors, and is maximal only when the plug is fully inserted, so avoiding a serious spark. I know of no commercial design like this, but it should be fairly easy to make.

Consider this option:

Locate the charger on the chair, connected at all times to the battery, but only energized when charging. Just make certain the charger has a reverse-flow diode to prevent discharge when not powered up.

I am sure a charger can be designed to fit available space, if a standard unit is not available.If you need help, contact me.

This will add a small amount of weight to the chair, but should not be prohibitive.

Your amps will be reduced by a factor of 10, and a low insertion force connector should be easy to find for 120VAC.

If a standard receptacle is not to much to handle, then problem is solved.

Note:

In addition to the aforementioned advantages, it enables the user to charge whenever they are within reach of a receptacle, such as in a waiting room, etc.

This will extend the life of lead acid batteries by keeping the charge level up and preventing sulfating of the plates.

Retractable power cords are available, as well as the "curly Q" slinky shape rubber cords.

I don't know exactly what you feel is low insertion.

Have you tried the connectors used on golf carts? I have a john deere gator that charges with 42V at close to 20 amps. The connector is fairly large, but is designed to last for years, and cannot be plugged in backwards.

As usual a lot of very good answers addressing the problem as stated. At the moment all wheel chairs whether European or American use the same charging plug. Why would you want to go down the road where the time will come when you will be stranded and unable to charge your chair. I know that here in Australia a stranded person can be got going by our road services people as the power plug is standard for all chairs. Many power chairs have at one time or another had onboard chargers and then gone away from them. I don't know why but if it worked as well as it should on the face of it they would still be built in. As you said, you are using gel batteries, 8amp is maximum charging rate for them. See previous forum threads.

I am employed by The Center For Cerebral Palsy in Australia and i agree that that the current connection is not the greatest but the fact that it universal ( at least in the western world ) far outweighs the disadvantages.

I'm active on a website that deals with people wanting better chairs, run by a fellow that builds chairs in his bedroom that put the mobility industry to shame.

Our organisation also made our own chairs at one time but we no longer do so because we can't afford to crash test them. As a spinal cord injured person i would think that you would agree that crash testing a chair should be mandatory.

"As you said, you are using gel batteries, 8amp is maximum charging rate for them. See previous forum threads."

I think that you should revisit those threads.

Re:- Mandatory crash testing ....

An individual is not an organisation and thus may build or modify how he or she wants for their own benefit / requirements or enjoyment.

G'Day Woody. I have just revisited those threads and i still maintain that recharging at 8 amps is the maximum for gel cell batteries.

Re:- Mandatory crash testing ....

An individual is not an organisation and thus may build or modify how he or she wants for their own benefit / requirements or enjoyment.

The OP said that a guy was building wheelchairs in his bedroom, being the plural tense i assumed that these were for sale, and thereby illegal in the US and AUS. without crash testing.

Charging Amps depends on the batteries internal resistance.
http://www.mkbattery.com/images/VRLA_TechManual.pdf
page 3
BM's 3rd and latest ... in progress ...wheelchair.
http://www.wheelchairdriver.com/BM-MK3-lithium-battery-powerchair.htm

g'day again Woody, i have just looked at your links and i must say i am impressed. I also like the chair. It looks like the sort of chair the OP wanted. It certainly should sell well and help a lot of people meet their needs.

regards

Jim

His reasons for requiring a 50 Amps capability in the connector is that it is also used during discharge and the chair motor may draw a lot of current when starting from stall.

All the chairs we are getting nowadays do come with switch mode chargers, indeed the chairs that had chargers built in were also switch mode. The cord used the IEC socket and so was universal, at least at the charger end. So there is no price advantage.

Most of our clients take their chargers with them anyway so i do not know why they are no longer built in. I guess that the ingress of water may be the biggest problem.

The motors in most chairs are rated at between 50 and 80 amps.

As a spinal cord injured person, I think the safety Nazis are the worst thing to ever happen to chair design! They are the biggest reason I can't BUY a decent chair that meets my needs, and am forced into building my own... (fortunately I CAN build my own, I feel really sorry for those who are unable to do so, either because of handicap or lack of knowledge / skills / etc.)

The safety "we can't allow any kind of accident to happen" mentality means that I end up with an obese tank of a chair that can't get into tight spaces, doesn't maneuver decently, weighs a ton, built with obsolete battery technology, that beats me half to death on any surface rougher than a perfectly smooth floor, and gets stuck on a regular basis...

I want, and am building a compact (seated width by seated length) chair, with soft squishy ATV tires that soak up bumps instead of passing them through to my body , and giving better all terrain travel ability, with handling like a "sports" manual chair, and potentially using modern LiFePO4 battery technology, with it's greater power density and weight savings potential. I am willing to accept the fact that the "cost" of such a chair is that if I get stupid it WILL flip me over and spit me out...

I would also add that I'm a paraplegic with good upper body strength and hand control, along with a strong demand for a chair that restricts me as little as possible, and lets me do as much of what I could do pre-injury as possible. A person with a different set of handicaps, especially ones that leave less ability and reliable control will have different needs and priorities... For instance I do not need or want the support and functionality that a quad would find essential....

As to charging sockets - at least as long as I keep using a mobility controller and joystick pod, the XLR connector is still there and usable if one wants a slow charge. However according to the technical data sheets on MK gels, Odyssey "red top" AGM's etc. it is DESIRABLE to charge at much higher rates than 8A, as long as you don't exceed a certain voltage, and don't allow the battery to exceed a certain temperature. This can be well in excess of 50A initially, though it will rapidly drop down to a lower value.

Ideally one should initially charge with a CC (Constant Current) bulk charge that holds the current at the maximum recommended value or the maximum charger output, and lets the voltage go to the maximum voltage for the battery type. This will quickly restore at least 90-95% of the battery charge, usually in less than an hour. Then the charger should switch to a CV (constant Voltage) mode that holds the voltage at the recommended value, and lets the current float (it will be at a very low value) for the next several hours, bringing the battery up to about 99% charge. When the current drops to about the 0.1C value, the charger should switch to a lower "float" voltage which acts to both bring the battery to 100% charge, but also acts to counter the loss from self-discharge (and possibly any parasitic current drains) and keep the battery at 100% charge indefinitely.

My understanding from various sources is that the reasons the chair makers got away from the on-board chargers was that they proved to have bad reliability problems - vibration from the poor suspension and hard tires was a problem, so was water ingress. If potted and sealed sufficiently to prevent vibration and moisture issues, then overheating was a problem, especially if trying to keep the package size reasonable... Far easier just to do an external charger that doesn't need to be as robust or environmentally protected, and can be larger, fan cooled, etc...

If you have no objection i would like to pass your post on to the local ( Western Australian ) manufacturers to see if they can help.

I suspect that most people in your physical state self propel and so the demand has not been seen.

Given the huge variety of wheel chairs that come from the US i am surprised that you cannot find one to suit. Perhaps, as you say, stability and litigation issues have stopped manufacturers from going down that path. Maybe the Segway people could branch out? Maybe you could modify one yourself?

regards

Jim

No problem at all with sharing my posts, I'd love to see any of the chair companies start building a chair like what I'm working on. After double checking the rules it looks like it is OK to point at another site, so I would also suggest pointing folks at WheelchairDriver.com. It's the place where I've gotten much of my information and design ideas from - LOTS of information there, with some strong opinions, which I tend to share...

While I don't hold any of the various OT/PT/MD types personally to blame, it seems a common thing in the rehab industry to do everything possible to stick paras in manual chairs, as if loosing the ability to walk isn't enough of a handicap - they want to take away your arms as well, by forcing you to use them for propulsion. In addition the long term prognosis for any manual chair user is rotator cuff / shoulder failure, requiring expensive, painful and only somewhat effective surgery to repair. On wheelchairdriver, we get at least one or two new users every week who start their first message with "New power chair user, due to shoulder problems caused by 'n' years of pushing a manual chair...." In effect the manual chair has turned them into "functional quads" by leaving them with little or no ability to do anything useful with their arms...

Even ignoring that, a manual chair greatly limits the distance and terrain one can travel over, is physically exhausting, and limits what you can do - anyone who says otherwise, I say to get in the manual chair, hand them a cup of hot coffee / bowl of soup, and tell them to cross the room, and maybe try going through a door, or across a threshold...

For more fun, try doing a bunch of errands with a manual chair, doing the suggested drill of transferring to a car seat, and taking the chair apart and stuffing it in the back seat, then putting it back together again at each stop to repeat the process....

My opinion is that arms are to precious a resource to waste them on propulsion! Instead, I want a power chair, coupled with a drive from the chair accessible minivan or equivalent for distance... I will shortly be getting a van (with the help of Mass. Rehab) but even now, it is no big deal for me to do multi-mile trips in the power-chair that I would never even want to attempt in the manual.

I've seen some of the modified Segway style chairs, and not been all that impressed - the nature of the platform limits the ability to run wide tires, and seems to also have problems with overall width. It seems to me like they are looking for a lot of "cool factor" without really getting a lot of benefit from it. As a side note, John Williams (aka "Burgerman") who runs WheelchairDriver did some early testing on the IBOTs, and was far from impressed. A few weeks ago I encountered a lady who owned one, and said that she was afraid to use the standing or stair climbing modes after it had jumped her off a second floor porch, and done a few "face-plants" without warning.

ART

This sounds like a neat project. Can you post pictures as it progresses?

Are you aware of these guys: http://fandl8020.com/index.htm and other industrial "erector-set" suppliers?

Odd thought. Since this is almost a brainstorming session, I'll suggest something:

Ever thought about some sort of "assist mechanism". Say something like, put connector here and in your case, push two buttons, one in each hand that would finsh placing the connector?

And it would work manually without any power. It just would require more force?

I'm thinking on the lines of an RC servo.

Remember that these are random thoughts for stimulation.

Here is a better page for the 80/20 stuff: http://stevenengineering.com/tech_support/8020.htm