DC to DC Charger - Ignition Switch Alternative?

[0truck0]

10+ yrs ago I was involved with alternator sales.... They were set to peak at 1800rpm, so your 130 amp alternator will do 130 amps at 1800 rpm, but not at 1200 for example. You will be driving at closer to that 1800rpm number so nothing to worry about, just keep in mind at idle, 700 or 1100, is not the full output of the alternator. of course, simply changing the pulley size on the alternator will change the speed and the relationship of engine rpm to alternator rpm, so you could run lower engine rpm and have alternator peaking just by using a smaller pulley. I would advise against this unless it is something very important in a specific situation. lol. Probably should not have broached this subject, but there ya go....

 

[justinm001]

of course, simply changing the pulley size on the alternator will change the speed and the relationship of engine rpm to alternator rpm, so you could run lower engine rpm and have alternator peaking just by using a smaller pulley. I would advise against this unless it is something very important in a specific situation. lol.

This is how mine is, I think a 2.5" alternator pulley against a 7" drive pulley. Mine is designed to be used for passenger busses thT have OTR bus air. My alternator rpm is a lot higher than the engine. I had to enter this calculation into mu wakespeed and its still way off. Which BTW wakespeed can control alternator based on rpm so shut off when under 1000rpm. Although I have a detroit S60 so have plenty of power.

I gotta switch this to a 48v alternator though

 

[carpkernel]

I think the idea is perfectly sound assuming that the current on the 12v side is comfortably within the limits of the device.


You can buy adjustable voltage window switches cheaper than the 'battery protect'. For example, any PWM SCC (which can be ~$10) has that on its load ports. The issue is that then has to control a larger current switching device. While you can DIY it all for cheap, you can't really DIY it much cheaper than it already is if you are buying non-Victron stuff.

For example, in the RV world they just generally call this device a VSR (voltage sensitive relay) and i have bought one for as little as $13 on Amazon. Here is one for $16: VSR

If you open that thing up all it is is 2x 70a 12v relays soldered to a circuit board that has some voltage sensing stuff on it.. In other words, it SHOULD be cheap!!

It will be more subject to unreliability from the quality of connections you make on the bottom (heat buildup), than unreliable because it's $16. The only way you could seriously improve the reliability of such a device, in my opinion, would be to use a solid state relay instead of mechanical points. An 'SSR' also sometimes referred to as optocoupler (although that's really only part of what an SSR is) has no points to get damaged from the arcing of inrush currents when it switches. So you could buy a 100a SSR and a $10 pwm SCC (which would make your voltage setpoints adjustable!) and build the equivalent device in totally solid state form for <$40, which i think is what the Victron piece is (and has some other cool functions). If you don't care about the Victron name or it being solid state you could just buy any generic VSR off amazon for <$20 and run it until it breaks, or more likely.. doesn't.

I stumbled across your post and I'm hoping someone can help. I've got a Renogy 20amp DC to DC charger however it requires a D+ wire. My cars alternator isn't exactly in a easy place to pick up th D+ wire and its also a smart alternator.
Can I use a relay/solenoid instead of using a D+ wire ?
I'm looking at an easy way and a safe way to install this without the fear of draining the car battery.
If I can use a relay/solenoid is there a link of what I need and how you go about wiring it up.
Any help would be great.
Cheers Guys.

 

[HarryN]

For a trailer, a possibly better method is to put an inverter at the starter battery and run 120 vac back to the trailer.

A 10 awg wire running 120 vac is pretty strong and can carry - at least in theory - 3 kW. That is challenging to do by by using DC.

If something goes wrong, the arc will also be a lot smaller.

 

[Stircrazy]

I stumbled across your post and I'm hoping someone can help. I've got a Renogy 20amp DC to DC charger however it requires a D+ wire. My cars alternator isn't exactly in a easy place to pick up th D+ wire and its also a smart alternator.
Can I use a relay/solenoid instead of using a D+ wire ?
I'm looking at an easy way and a safe way to install this without the fear of draining the car battery.
If I can use a relay/solenoid is there a link of what I need and how you go about wiring it up.
Any help would be great.
Cheers Guys.

you can pick any source that is hot when the car is running and not when it is shut off. I used an upfitter switch that was only hot when the truck was running in my pickup. that way I have control of when its charging and when it isn't