OpenEVSE - Open Source Charging Station

[JeremyW]

Question for Chris or Glenn or anyone who's an OpenEVSE expert:

I had a chance to get a calibrated amperage reading of my vehicle draw the other day and it showed 15 amps dead even, while my current meter connected to my OpenEVSE showed 16.2 amps. Where can I change the calibration settings for the current transformer?

Been very very happy with my OpenEVSE. The charge timer works great and never fails to charge my car!

[GlennD]

If you are using the internal current metering then modify the calibration factor. the default is usually good but it is easy to modify and reprogram. Try a value of 240 first. Go up or down from there.

It is easy to mod but you must reprogram each time. I think Lincomatic has a utility to set the value but I have not used it.

[camasleaf]

I decided that I will need a portable EVSE. I ordered some parts from OpenEVSE (board, display, CT and J1772 cable). I have two Crydom D2450 50A solid state relays and I will first try to use them, if they get too warm I will switch to a contactor. I have some questions about how the board will come set up: for one contactor or for two relays. I will do some reading about that later.
My main question right now is if I need to use 240V fuses or not. My goal is to keep everything safe and as small and light as possible. 40A fuses and fuse block will take some space. I was thinking of finding fuses that will bolt one end directly to the relays, eliminating the block and some wiring. I will still need to support the fuses properly. The 50A OpenEVSE does not seem to have fuses included in the kit. The 30A does. What is the rationale behind the decision? How important are those fuses?

Thank you.

[jpadc]

The 50A OpenEVSE does not seem to have fuses included in the kit. The 30A does. What is the rationale behind the decision?

Not an expert on OpenEVSE just an owner, but the 50 amp kit has a 50 amp contactor/relay which then leads directly to the 50 amp J1772 cable so all the components that are ever connected to the 50 amps can handle the load. The 30 amp kit has only 30 amp relays. if you are traveling with an EVSE (like I do) to campgrounds where you might plug into a NEMA 14-50 outlet but only have 30 amp capable relays, you can see why that might be less than safe without the fuses.

I wanted my OpenEVSE setup to be able to be used at both 120 and 240 volts (unlike their 50 amp kit) so I got the board (and display) but used a 120 volt 50 amp contactor to avoid the problem. The solid state relays you mention are only good for 25 amps (I think) which at about 28 amps continuous load (assuming a car with a 6.6 kW charger) would be overloaded by a good bit. Of course you could set the charging amp limit lower. However, you might still want to fuse protect that setup if you plan to use 14-50 type outlets.

[GlennD]

I decided that I will need a portable EVSE. I ordered some parts from OpenEVSE (board, display, CT and J1772 cable). I have two Crydom D2450 50A solid state relays and I will first try to use them, if they get too warm I will switch to a contactor. I have some questions about how the board will come set up: for one contactor or for two relays. I will do some reading about that later.
My main question right now is if I need to use 240V fuses or not. My goal is to keep everything safe and as small and light as possible. 40A fuses and fuse block will take some space. I was thinking of finding fuses that will bolt one end directly to the relays, eliminating the block and some wiring. I will still need to support the fuses properly. The 50A OpenEVSE does not seem to have fuses included in the kit. The 30A does. What is the rationale behind the decision? How important are those fuses?

Thank you.

The 30A kit is rated for 24A continuous and has the max fuse size available at 30A in that form factor. 80% of 30A is 24A. The 50A (40A continuous) relies on a 50A external circuit breaker sense 50A fuses are generally very large.

Solid state switches may be used but they are dangerous sense the failure mode is shorted. I also doubt you will find room for the large required heat sinks. The OpenEVSE checks for shorted contacts and for that matter a shorted switch. It will give you a failure but there will still be voltage at the plug. If you exercise some common sense and unplug the unit upon a failure display you will be all right. The standard assumes you have no common sense and it try's to protect you from yourself.

[camasleaf]

Thank you both for explanations. I does make sense. The EVSE would not need fuses if only used within the right circuit. But with all the variations of plug adapters a 30A rated EVSE could easily end up on a 50A circuit.

I will still think about using the SSRs and heat sinks since I have them already. I also like the flexibility of having the 120V option. Still need to figure out how to put the heat sinks outside a waterproof enclosure and still transfer the heat.

One could take a contactor unwound the coil, split it in half wounded back and have a switch to parallel the two the coils to work on 120V when needed. Are there any 50A electro-mechanical relays that will work with the limited current supplied by OpenEVSE board? I would sell my SSRs and buy those.

[eHelmholtz]

There some Chinese made relays that are supposedly rated for 80A with a 12V coil so they work with OpenEVSE. The wires don't look anywhere beafy enough to use at 80A but appears to work fine at 40A. They appear to be the same relays that are used in EMW's Juicebox. Here's an ebay listing for one.
http://www.ebay.com/itm/1PCS-12VDC-80A- ... xyNThTdwIM

[camasleaf]

I have a 40A Eaton contactor that I just took apart, the contacts overheated because of a bad wire connection. Came from a Blink that was charging at 25A.

After looking at those relays on eBay, my idea with rewinding the coil on a contactor does not seem that crazy anymore . I am not sure I trust those relays even at 40A for very long. Any idea how big they are?

Thank you for the link. It is an option to consider.

[GlennD]

There some Chinese made relays that are supposedly rated for 80A with a 12V coil so they work with OpenEVSE. The wires don't look anywhere beafy enough to use at 80A but appears to work fine at 40A. They appear to be the same relays that are used in EMW's Juicebox. Here's an ebay listing for one.
http://www.ebay.com/itm/1PCS-12VDC-80A- ... xyNThTdwIM

I have used the Chinese relays that the JuiceBox uses. The 80A rating is a poor Chinese joke unless you also need a room heater but they work fine at half that or 40A. They are quite large. I doubt that they would fit in any of Chris's enclosures.

Chris's best option for portable use is the 30A (24A) unit. The two relays he uses are small and the unit is fuse protected for portable use.
Remember it does not really matter what circuit you are plugged into since the EVSE limits the current via the pilot duty cycle. Also the car charger only takes what it needs. An enhanced Leaf will draw 27.5A and not use any greater current. It also follows the J1772 protocol and if it is connected to a 24A EVSE that that is all it will draw even though the car charger could draw 27.5A.

A stock OpenEVSE unit will supply at L1 120V twelve amps. At L2 240V the default is sixteen amps but it can be set in 2A steps to match the available current source.

Remember the car sets the charging current as long as there is enough. A 30A EVSE is the same as the 80A spec max. The car only takes it max current. Thea is why first generation Leaf's were able to use Solid State Relays. Even at 240V they maxed out at 16A.

Currently the only cars that can charge at 40A are Tesla's and Tesla power train cars like my Mercedes B Class or the discontinued Toyota RAV4 EV. Everything else is 30A or less. As I said, An enhanced Leaf charges at 27.5A at 240V.

[camasleaf]

Thank you Glenn. I will likely go with a 40A contactor and sell my SSRs and my 40A semiconductor fuses (they are big). I know that the car dictates the current, but if I spend the money and put the effort into building an EVSE I want to have the full 40A continuous capability. I am not sure how I will make it work at 120V, I am still brainstorming about that.