I am to have a 12v relay used over my awesome lipo4 pack at 36v. Since I balance all cells, I dont want to use power from just few cell to power the 12v relay. (though does anyone know of a cheap 50amp latching relay?)...
What are you switching. You may be able to use an N or P MOSFET which could possibly be configured to take very little power. But if you are switching 50 Amps the choice of MOSFET would be critical.
Otherwise you could use a step down switching regulator which would probably take around 45 Ma to drive your 12V, 110 mA relay. Suitable modules are available very cheaply on eBay.
I haven't found a 50 Amp latching relay at a reasonable price yet.
Can you please explain me how the dropper works. I just need 180 ohm in series with the coil? And then ofcourse a high power resistor? There must be 24v over the resistor so it must be like 24v x 0,15 amp= 3,6watt and then you rounded up till 5watt?
It doesnt matter if it draws wattage from the whole pack. The relay will shut off when the voltage of the cells get too low.
I dont want step up, thought it could step down aswell. Maybe it can...!!! Doesnt matter for now, I should really just use dropper resistor. Problem is... i never get time enough to do the electronics I have some understanding about. I just...dont...have...the...time.....at..all!
What are you switching. You may be able to use an N or P MOSFET which could possibly be configured to take very little power. But if you are switching 50 Amps the choice of MOSFET would be critical.
Otherwise you could use a step down switching regulator which would probably take around 45 Ma to drive your 12V, 110 mA relay. Suitable modules are available very cheaply on eBay.
I haven't found a 50 Amp latching relay at a reasonable price yet.
I will probably use those swithing regulators. Seems to be a good way to do it. This seems to be able to handle the input voltage at 42v and the output voltage and needed current.**broken link removed** Now I just need to know what to do to fix my issue till thursday, when I needed 15 devides done Why my boss sell stuff he knows too little about !!!!
The relay has to be able to handle peak ampere at 60 amps, since it drives a motor etc. 20-60 amps relay is needed.
A pair of 50 A or 75 A power MOSFETs (for redundancy) and a simple latching circuit will cost waaaaay less than an equivalent mechanical relay. You can use about 10 microamps of current from a battery to maintain the latch state, not nearly enough current to upset the stack charge balance. What is the voltage across the relay contacts now, 42 V?
Yes, I agree, but most are SCR and tend to have zero volt switching. I would be interested if you know of any 50A DC switching solid state relays: I could not find any.
For a quick and simple solution Alec's suggestion can't be bettered.
(The resistor will dissipate 3.6W so use a 5 Watt, or more, resistor bolted to a heatsink of some sort, case of equipment for example.)
A pair of 50 A or 75 A power MOSFETs (for redundancy) and a simple latching circuit will cost waaaaay less than an equivalent mechanical relay. You can use about 10 microamps of current from a battery to maintain the latch state, not nearly enough current to upset the stack charge balance.
If you use a buck regulator, the inductance of the coil itself will mean you don't need a separate inductor.
If you use something like an LM2576HV-ADJ, with an output load of an 8.2 Ω resistor, and have the relay coil in place of the inductor.
The LM2576HV-ADJ will control the voltage on its feedback pin to 1.23 V, so there will be 150 mA flowing in the load. All the load current comes through the inductor, so its average current will be 150 mA as well.
If you do that, you must not put any capacitors or diodes in parallel with the coil, and it's a good idea to have the coil close to the buck regulator. The resistor will generate a bit under 0.2 W of heat, so a 1/2 W or more resistor would be best.