[GoElectric]

Hi. We are using a Curtis 1238, which has pre-charge protection, but have been told there could still be damage to the charger and/or DC/DC when switching pack voltage. I'm willing to go with this, but wonder if anyone has any comments, especially regarding resistor size and power rating. I was thinking something like 100ohms and 10 watts.

Thanks.

 

[GoElectric]

Hi Tony,

The HV doesn't touch a lot more than that, unless you include the contactors themselves, lol. Yeah, there will probably be some heating elements, but as you say, no-worries there.

What is the 5X rule (for overload protection?)

I came up with 100ohm/10W from the spec on another build, which needed it for the controller. That one was 25W and as big as my thumb. I think since the controller is already protected, that would have been the bulk of it. So, 10W sounds good and safe as long as it doesn't set off any alarm-bells for anyone here.

The 100ohm value I think I would keep the same - the resistor is still doing the same job, just not as much of it - again, unless someone says otherwise.

Thanks.

 

[GoElectric]

Being an EE does give you some cred but it all depends upon experience. I know guys with engineering degrees who are smarter than me, but have no practical grasp of anything outside of their specialty. It helps if you have a great memory, which I don't.

Speaking of practical then, you are saying some resistors have a better overload rating than others? I'm guessing the little white ceramic ones are not the best then.

When you say PTC, I think of positive temp coefficient resistor, is that right? I thought you meant something to do with the heating elements, but I think not. I see what you mean - that is a cool way to pre-charge, very safe.

As far as overload goes, worst-case I will have 150V (pack voltage) across the resistor, or 1.5A, which is a ton of watts, and maybe it will cause a failure. I guess I can wait and see how long the pre-charge takes, but I'm guessing less than a second. It will all be set up on the bench soon.

Thanks.

I will look and see what I can find on here about pre-charge failures. I expect all of them will be protecting the controller too.

 

[GoElectric]

So far, nothing which applies to the question of the difference in pre-charge between cars which need it for the controller and not. Actually, I haven't seen an actual value for pre-charge yet (?).

 

[GoElectric]

Hi SS,

Thanks.

As I understand it, inrush current can damage the DC/DC and/or the Charger. I don't know how common this is, but if a single passive component can prevent it, then unless someone can convince me otherwise, I'm up for something. I just wonder why these components, which are built for such an event wouldn't be ummm, built to WITHSTAND such an event.

I like your idea of using a light so I can see what is going-on. I wouldn't use it permanently, but I should have thought of that. Should be able to scrounge-up a halogen light somewhere.

I squared R means 1.5 amp across a 100 ohm resistor is 225 watts, not 25 watts. I can imagine that might cause a cheap resistor to fail eventually, even if it is only on for a second.

 

[GoElectric]

Sorry, I suppose there are people who don't know that. I should have said "for a fraction of a second."

Is there nobody out there who has a precharge?? What size (and why)?

 

[GoElectric]

Hi - Mr. P. and that is good to know. I assume you are talking about a Soluton(?) controller?

Anyway, the max current you are getting is roughly the same as what I will get with 150V and 100ohms, so that is good. And 10 watts sounds reasonable.

Awesome, I think I'll go watch some porn (just kidding).

 

[GoElectric]

Hi. Yes, I know the 1238 has precharge, but am not sure about the charger, or DC/DC. I am thinking 50-100 ohms, and like the idea of the PTC, but don't know if it is necessary - I guess it could be considered a safety feature in case of a failure? Otherwise, if designed correctly, I'm not sure why the precharge would ever go on too long.

Thanks,

Jim

 

[GoElectric]

I guess what I was thinking was I might prefer to have a fuse which just blows, so I know where the problem is. I can see the use of a resettable fuse for a motor or something which might draw too much current. When it re-sets, one can adjust the motor controls or load (not thinking of an EV here), but if my charger or DC/DC draws too much current, I don't want it to turn on again until I fix it (?).

 

[GoElectric]

Thanks Tony - I appreciate it!

Jim