"Simple" Electrical question. - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 04:37:56 pm
content: Ok, I am a beginner, and amateur.I am wiring a 12v engine coolant pre-heater into my truck.This is a device that features 4 glow plugs, each of them is 300w, for a total of 1200w.I have two 80a relays and I have 2 glow plugs wired to each relay.So each relay controls two of the glowplugs and is 600w each.I also have a three way switch.This switch is 0 in the middle, and 1 in the other two positions, with a red & blue LED.I want one side of the switch to provide 600w, and the other the full 1200wSo I need a diode of some kind between the remote input (86) on the two relays.I made a drawing below.Question: What kind of diode should I use? I can't imagine it will see much current. I'd say max voltage is 15v, but I'd go 16v just to be sure.Any other way of doing it? In advance, Thank you

author: Morgoroth
author_rank: Regular Contributor
timestamp: February 08, 2016, 05:04:33 pm
content: I'm no familiarized with automotive environment but seems like you only have control signal over the switch lines, so probably will only run few mA, in worst case, 50mA or 150mA to feed the coil of the relays. Anyway check relays datasheet to be sure about coils currents, they will tell you how much current the diode must handle under this criteria.One more thing, as far I know, trucks and automotive environment in general could be very nasty for electronics, meaning a bunch of noise, huge voltage transients and backwards voltages all around, so probably is not so simple as add a diode and 'that's it', probably a good design involve more protection.A 1N4007 should do the job, handle up to 1A and have a forward voltage of 1.2V at 1A.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 08, 2016, 05:06:27 pm
content: It would only carry the current of one solenoid so almost any diode would do just fine.1N4004 (Plain diode 4 Amps) would be alright. If you don't have it on hand just rip any chunky looking diode from an old computer power supply.There are other ways of doing it without a diode but I'm not sure if it is worth the hassle.One thing you definitely want to have is pilot lights for both heaters.Also I would wire two glow plugs in series. This would halve the power but it will quadruple the life of the glow plugs. Since they are in contact with water they might not get hot enough, so their power draw would be higher than normal. Wiring them in series eliminates that problem.

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 05:20:14 pm
content: The glow plugs are rated for 300w each, and I have them wired in parallel, Max Power !!!In addition to the LED lights on the switch, I have the switch/relays coupled over the ignition, so they only works with ignition ON.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 08, 2016, 05:22:40 pm
content: Quote from: SantaClaw on February 08, 2016, 05:20:14 pmCarry on then. I'm not your nanny

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 05:35:02 pm
content: It's wired (in parallel) like it is on cars that has this heater stock, they are not ordinary glow plugs.

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 05:39:37 pm
content: Quote from: Morgoroth on February 08, 2016, 05:04:33 pmI happen to have 10 1N4004's can I just put two in parallel to double the current handling? If I wanted I mean, or maybe they don't work that way...

author: Morgoroth
author_rank: Regular Contributor
timestamp: February 08, 2016, 05:53:38 pm
content: again, check relays datasheet to be 100% sure about how many current you will use, and yes, putting two diodes will probably split the current (I never done it before).

author: ZeTeX
author_rank: Frequent Contributor
timestamp: February 08, 2016, 06:05:55 pm
content: Quote from: SantaClaw on February 08, 2016, 05:39:37 pmyou can parrael diode but dont forget power disspation. (voltage drop across diode times the current), divdied by the amount of diodes.

author: john_p_wi
author_rank: Regular Contributor
timestamp: February 08, 2016, 06:19:04 pm
content: Umm. 1n4004 are only rated at 1 amp, 400 volts. Just use a DPDT switch on-off-on. Also, expect the heaters to be near a dead short when cold - they may consume far more current for a short time than the relays can handle.

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 07:24:28 pm
content: I have tried over-sizing everything.My truck has a 185A (idle) alternator 280A high idle.I've got two 80A relays.Each pair of glow plugs are rated 600w @ 12v = 50A for the pair. With 80A relays I have a 30A overshoot, per relay.My truck however, charges at 14.4v, so at 600w that's 41.6A or 38.4A Less than rated per relay. Neary 50%I have soldered most connections. I'm using approx 25cm length 8mm² copper wire for EACH glow plug. Though they are all grounded through a shared single 10mm² copper wire (15cm long).Total wire length from battery to the glow plug is approx 40 cmEach relay is fused separately, with A 80A "maxi" fuse. There is a 25mm² cable from the battery to the distribution/fuse block.Below is a picture of the heating element itself, don't mind the crimp connectors in the pic. I used yellow bullet connectors on the glow plugs that I stripped of insulation and soldered directly to the wires after crimping them. Covered with shrink wrap ofc.The relay spade connector size lies a bit, as they are massive, approx 10mm wide.I will post pics of how it looks in the truck tomorrow, it's too dark and cold outside for it now..

author: rickey1990
author_rank: Regular Contributor
timestamp: February 08, 2016, 10:10:20 pm
content: Remember there no harm in using two switch's, or even four 300watts each. it may not be fancy but its the safest and most reliable. Diodes dont regulate, they dissipate the excess as heat.

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 10:12:44 pm
content: If I'm only putting 150ma through it, will it still heat up as if I was putting 1a through them ?The relays aren't pulling much current at all, I haven't measured it, but I'm guessing 150ma max.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: February 08, 2016, 10:27:23 pm
content: Quote from: SantaClaw on February 08, 2016, 10:12:44 pmif the diodes are passing 150mA then they will be heating much less than if they were passing 1A, roughly 150/1000 as much.Not entirely sure why u need the diodes though. Or are you talking about freewheeling diodes across the coil?

author: Unknown
author_rank: Unknown
timestamp: February 08, 2016, 10:28:56 pm
content: Using a three way switch, The one I've got, how else can I get 1 relay to fire on one position and both on the other ?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: February 08, 2016, 10:33:15 pm
content: Sorry I get it now, I just skimmed the thread, that red line is the diode.I think your diode logic is ok then.

author: rickey1990
author_rank: Regular Contributor
timestamp: February 08, 2016, 11:30:49 pm
content: OKAY! i get your idea and yes it will work, my only problem is this little fort in the back of my mind about safety. i want to tell you the safest way of doing it, well my forts on it. different people have different ways of doing things. call it a curse. diodes are good at blocking reverse voltages. its the same way i build alot of my old school robots. using the same input device to get two different results. however like in the circuit below yours, its being used as a safety device only blocking the reverse voltage if there's something wrong causing the reversed voltage.I do like our idea of splitting up the 4 elements into two. Save the battery from the onslaught of using 1200watts from a cold start. But i am use to motorcycles so please take anything i say with a pinch of salt. Asking a trained mechanic is probably your best bet.

author: Delta
author_rank: Super Contributor
timestamp: February 08, 2016, 11:52:17 pm
content: The current through the glowplugs will not be less at 14.4v than at 12v, it will be more. They are simple resistive devices.Your diode logic plan is sound, it will work fine.Don't worry about the current rating of your diode, it's only powering a relay coil.Will 1200W even make a dent in the thermal mass of your engine? I can't see it doing much at all apart from loading down your electrical system...

author: Unknown
author_rank: Unknown
timestamp: February 15, 2016, 12:06:08 pm
content: Ok, went with a double sided switch as suggested, and dropped the diode idea.Question 2, can I put a constant load of 700a++ through a 1000a current shunt resistor without it overheating ?http://www.ebay.com/itm/281318471555?var=580357103832<--- the 1000a version.I am asking as I planed to fit 1 on the positive going into each of my two 9700w amps. They have a constant current draw of about 750 amps each when running @ max power.I would say that an amp draw in the range of 300-400a would be normal for it. But short term, maybe up to 900 amps.I have no idea how warm that would make it.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: February 15, 2016, 12:29:19 pm
content: I'm going to have to ask... Where is the 1200W at 12V coming from?If it's being supplied from the mains, that will need a hefty and expensive 12 power supply. Wouldn't you be better to use mains voltage heaters?If it's coming from your truck... well if the alternator is running then so is the engine so you don't need the coolant heaters.If you are expecting to warm up your truck engine by drawing 100A from your truck battery without the engine running, you will have a very flat battery in a very short amount of time. Especially if the battery is as cold as the engine which needs preheating to start.

author: Morgoroth
author_rank: Regular Contributor
timestamp: February 15, 2016, 01:17:56 pm
content: the truck if for the battery

author: Unknown
author_rank: Unknown
timestamp: February 15, 2016, 01:36:29 pm
content: Quote from: DenzilPenberthy on February 15, 2016, 12:29:19 pmI do write the answer for you a bit further up. But I will save you the trouble. This heater is not intended for use with the engine shut off, it's for getting the heater going quickly after it's started. It must NEVER be run without the engine running, as the hoses\heater will overheat within minutes due to the size of the hoses, and the location of the heater (top of the engine) As for running it on my batteriesWould you imagine that I have 570 Amp hours worth of AGM batteries in my truck, so in theory I could run it for 6 hours +++ without any problem. However, as stated above, this is only going to be used with the engine running. The truck has an alternator that outputs 185a on idle speed, and 280a on fast idle. More than enough for it to not only run the heater, but even charge the battery at the same time. Though, for the first minute or so, it will be pushed as the engine glow plugs will be doing "after start glowing" for a minute or so, That's the stock 9 glowplugs.8 - 1 on each cylinder, not sure how many watts they are, and one heating element in the intake, just before the turbo. I suspect 800-1500wBatteries:2x Stinger spp1500dc - 65 AH each 110 AH.1x Stinger spp1200 44 AH2x EG 200-12 EUROGLOBE AGM, 208Ah a total of 416 AH570 Amp Hours total.Though, the stinger batteries are insulated from the rest unless the relays\stereo is on. I can override for an extra boost.

author: dwpatter53
author_rank: Contributor
timestamp: March 01, 2016, 11:23:56 pm
content: Do you have properly sized fuses for each pair of heaters??You do not want to have a fault with out protection. You could melt the wiring or start a fire.

author: Unknown
author_rank: Unknown
timestamp: March 01, 2016, 11:25:02 pm
content: Quote from: dwpatter53 on March 01, 2016, 11:23:56 pmyes each pair has a 60 amp fuse.