Automotive electrical solenoid question

[russrmartin]

Hi all. Hoping someone out here has some experience with the automotive industry and sizing battery supplied energy conductors and solenoids.

I have a client who has asked that we essentially install a contactor which will act like a solenoid on a unit such that when they press an estop, battery power is killed to the unit. The battery system is remote to the unit, so I don't have information yet on the length of the cable, I only know at this point that the unit is supplied with 2 12V 1400CCA batteries.

I am struggling to determine how big is big enough on the contactor. I'm not sure even what questions to ask at this point. Is CCA a rating I can base my sizing on? How do you derate things? At 1400A battery cables would be in the MCM range or larger, and they are not, so there clearly is some way to derate based on lenght, or cycle time. If you have sized a solenoid for the automotive industry, you probably know exactly how to go about sizing a contactor for this purpose.

[dleakey]

Idk if it helps, but Borg Warner makes replacement automotive solenoids. The old standby that most people call a "Ford External Solenoid" is just a relay (4 pin, NO). It is Borg Warner part number S5049. I know that O'Reilly carries these. You may be able to find info on Borg's website or go to a local auto parts store to look at their books. This solenoid was used on many fords. I know for sure 1988 Mustang GT 5.0 had one if you need an application. Happy hunting.

[kittydog42]

Go with an Albright SW series or Kilovac EV series contactor. The Albright is open and the Kilovac is sealed. They come in sizes from 80 amps on up, but can handle more than that if it isn't continuous. You can get many different coil voltages as well. An SW200 with a 12VDC coil should work for you. You can usually get these from electric vehicle suppliers (such as golf carts or forklifts). They run around $150.

Stay away from actual automotive products like a Ford starter solenoid; they aren't continuous duty rated and if used as such they will weld shut. There are similar solenoids that are rated for continuous duty made by White-Rodgers (and others) that are sold at places like Grainger. These are only good for around 40 amps. These run around $25.

[leitmotif]

OK so you have batteries rated at 1400 CCA. That is your supply. Let us not worry about that for now.

Now let us talk about the load. This is starting point of fuse selection and cable size.

Dont let the "automotive" thing confuse you -- Ohms law still applies.

KNOW THY LOAD

So tell us what the load is and what current it draws. How are you turning it on and turning it off?

Dan Bentler

[keithkyll]

Don't want to break rules here, so please PM me for more info.
I have some surplus Albright SW series. New in box. 250 Amp. 24 (rated 28V) and 48 volt (rated 56V) coils. I assume you need 24 volt.

[russrmartin]

Thanks for the responses. Sorry, I was out sick Friday.

I failed to stipulate, this will be a safety relay, so ideally I'll provide a forced guided relay. I'm just struggling to determine how to size the relay such that it's sufficient and not overkill.

As Dan alluded, load is the critical base point. I am still trying to determine the load from the client. I think the load is going to consist mostly of the starter, which is intermittent load, and some very small continuous load for gauges, etc. As additional info, this is for a generator testing facility.

The purpose of the relay is dual, it will act as an immediate shutoff if an E stop is pressed and kill the engine immediately, and also disable the starter until Estop is reset. My big concern came with the length of conductors etc, since such low volate and high current could create some enormous contacts. I think these are minimized on vehicles because the cable runs are very short, but mine will be much longer comparably to a car or truck, so I'm worried that I'm really dealing with MCM cable and ridiculously large relays. I'm hoping that doesn't prove to be the case, but it has been awhile since I did anything outside the norm sizing conductors and components so far from the norm.

[leitmotif]

It sounds like you are building your own engine or building one up.
OK so this is an engine starting relay.
I dont know if you can get that in a safety relay configuration. However the current rating should be fairly easy to determine - talk to whoever built the starter. Dont forget there are other options
Air start - see Ingersoll Rand they have made starters for decades
12 V run 24 start. Cole Hersee has a relay for this and they have "regular" starting relays also. This seems to be going away and trucks are switching to air start.

Keep batteries as close to engine as possible to avoid voltage drop. On automotive and truck engines I would start with 2/0 at a minimum and increase as needed. This is critical on starter relay and less critical for control relays - in that case you may need to upsize wire for volt drop but there will be a big cost difference in the control size changes (12 to 10 etc) than on starter sizing 2/0 to 3/0 etc.

Since you are testing I would not do too many interlocks and safeties. Keep it as simple at this stage as possible.

Uh is this manual start or automatic start ie on a standby generator or pump? Check with Cat and see if they have an engine control package.

Dan Bentler

[todster]

The cranking current shouldn't pass through your contactor. It's already controlled. This should be direct from the battery to the starter solenoid. The current to energize the starter solenoid will be controlled.
The charging current if used, may want to be kept on a seperate circuit so that you do not risk powering the engine controls after the safety relay is activated.
The batteries sound like 8D's and probably were sized for duration rather than cranking power.
Instead of 12 volts, figure the current at 9 volts and that will cover start conditions when available voltage is lowest. Will the control voltage be 120 or 24? Either way, you should be able to find an estop relay that will fit the bill.

[russrmartin]

Dan, you are uncanny.

The application is an engine test cell for none other than the very Caterpillar you refer to.

In this application, they disconnect the charging circuit and connect to a remote battery pack. This is why the need to actually interupt the power, and also why opening said relay will kill the engine and also disable the starter.

Many test cells we work on have the air start, but many also have both to allow for flexibility in testing.

I am aware that the wire size is going to be large, it just would appear that I've forgotten how to correctly size conductors for load when one has to consider voltage drop. I've had it too easy for too long. Once we have the load information, I need to select a location for the relay, identify the conductor lengths, and determine the right size. I think then and only then I'll be able to know how big the relay needs to be. I'm thinking now the relay will be more a function of conductor size than anything else.

Do you think I'm in left field?

[leitmotif]

Originally Posted by russrmartin

Dan, you are uncanny.

The application is an engine test cell for none other than the very Caterpillar you refer to.

Many test cells we work on have the air start, but many also have both to allow for flexibility in testing. Do you think I'm in left field?

NO I do not think you are out in left field. Test setups can be dangerous especially so if a new unproven product. Saw video of diesel that came apart during dyno testing.

Let us "divide" your DC into two circuits and go from there.
CONTROL AND STARTER MOTOR CIRCUITS

CONTROL This is all 12VDC that is say 30 amp or less. I fully agree with placing batterie(s) for this outside the cell is a good idea. IF you are running grounded 12 VDC wiring I would consider Cole Hersee battery disconnect switches as an emergency disconnect - I believe these are Coast Guard and aircraft approved. If ungrounded I would use two switche or a single double pole I dont think Cole Hersee makes double pole.

STARTER MOTOR
I am going to assume this is 24 VDC since a diesel. I would put two or 3 batteries in test cell and the starter solenoid in there (it may be incorporated in the starter motor anyway ??).
Yes you could put batteries outside the cell and yes you can parallel conductors BUT how are you going to terminate them on starter motor?

The starter motor relay should be sized to handle max current from motor at about 10 VDC (ideally 12 VDC but batteries do droop). Now then assuming you are pulling 400 amp on starter and ASSUME the correct wire size is 4/0. Now all you need to do is get the resistance per foot value for your conductor (I assume SO type aka welding cable) and calculate voltage drop at the 400 amp at teh length of cable. You want this less than 3 to maybe 5% ie about 0.6 VDC. If you get more than .6 V then go to next larger conductor.

- Cat should know the current draw value on the starter motor.
- Do not forget to use total conductor length for volt drop calcs. The "gos in" and "gos out" ie + and - add together.
- IF you are testing engine under freezing temperature or less then you are going to need minimal voltage drop for sure.
- I would use NEC table for volt drop calcs.
- Weld cable sizing is for 50% duty and higher than that in NEC. Rome makes this plain on their weld cable tech sheet.

Dan Bentler