I'm not going to use it on a Ferrari. You connect the switch to the negative pole of the battery. Then you connect the negative cable to the switch. I don´t know how much the switch weighs so don´t know how much force there will be on the connections.
No way this is likely to sustain 200A let alone 800A. 200A require a 70mm² copper cross section. I even doubt this relay is any beefier than the old-school Bosch 40A. You may toggle the accessories through this, but not the starter.
Much clearer with those photos, and those specs are quasi-appropriate for a battery disconnect application (200A continuous, 800A surge), but I'd still agree with Ian that the terminal studs on the "relay" (and the relay itself) seem a little smallish. Typically, a battery cable terminal would mount to a 3/8" or 8mm stud (while those seem more like 1/4" or 6mm studs). That price does seems amazingly low, but this is always a problem with specs on relay contacts -- where the current capacity is inversely proportional to number of cycles (so it can pass a high current but for fewer cycles). If used on a moderate-compression 4-cyl Honda with a small starter, I'd be less concerned, but, on a big, bad 8-cyl or 12-cyl, the lifetime may be short IMO. Compare to this typical manual battery cut-off switch size (with no internal relay stuff nor internal electronics) and its terminal stud size (the overall dimensions are given down in the comments): https://www.summitracing.com/parts/joe-46200
I'm a noob when it comes to car electronics. Would something like this be better suited for a V8 (it's for my Porsche 928)? https://www.summitracing.com/parts/sms-t3-12v#overview
This one is probably much better. As far as I am concernee I do not disconnect the starter. From the positive terminal of the battery you usually have one dedicated cable for the starter and another cable for the other ancilaries. my switch disconnect only the later. As a result it does not have to bear the bulk of the amp draw. Even the cheapy relay could work if it does not have to crank the engine.
Do like the higher current ratings of this unit and the mounting lug is maybe larger diameter and thicker (but not 100% sure about that). This is a bit of a different beast being able to automatically disconnect at 11.8V if you (a human) forget . The instructions also have some good specs like its current draw being only 100 microamps in the disconnected state (the prior manual one didn't seem to have any such specs). I will say that I don't like "hanging'' any unit directly on the battery terminal and would suggest using a "chassis mount" arrangement like shown in the instruction -- but is this your project or mine? You jumped into this without giving any background, and I wonder if you aren't trying to solve a problem that you shouldn't be having in the first place. What is you present parasitic current draw when the key is "off"? Is it quasi-reasonable, and you are just so rarely using the car that you need to disconnect the battery?
I'm looking for a permanent and convenient solution to prevent a dead battery. I currently have the 928 on a Ctek trickle charger, but because the battery is stowed away below the spare tire, it's a pain to connect the charger. Also, there is no easy way to connect the charger. I have to crack open the sunroof in order to guide the charger cable to the battery. I used to have the manual disconnect in my previous hobby cars, but those were easy to reach. This remote controlled disconnect looked like a very elegant way to solve the problem. I don´t know (yet) if there are any drains, but you may know that the 928 has a lot of electrical stuff that could go wrong. I will also drive it sparingly. And if there's something I don´t like it's a flat battery. Thanks for the information on this topic, I really appreciate it!
I overlooked your post, but your suggestion might work too on the 928. Will have to check if the starter has a dedicated cable.
I received the switch from Ebay, but I won´t even bother installing it. The Ebay ad claimed 800A instantaneous current, but the manual in the box states 250A. So no use for my 928 (which according to Rennlist requires 650-670 CCA). The terminals on the switch/relay are tiny, I guess 4 or 5mm. I'm going to send it back.
First I will have the whole electronics checked by a mechanic. See if there is any parasitic draw at all. What are common causes for that in a car?
Improperly added electronics (alarm, radio, amplifier, etc.) or maybe a defective alternator/regulator. Don't know what would be a "normal" parasitic current draw for a 928, but anything much over 50 mA might need a tender (or disconnection) for 3~4 weeks disuse.
Ebay and Amazon have all kind of counterfeit junk. Counterfeit Electrical Components - Just Say NO! - Marine How To
