A better alternator delete

[Daox]

Hurray, the design is now all done. I decided on a method to view the charging dc-dc converter LEDs. There will be holes in the end plate with the plugs you can look through. I'll be making some sort of white light 'catcher' so the LEDs shine on to this deflector and you can fairly easily see blue/red/green.

Here are the most recent pics of the end plate and the whole rig.

[Daox]

Alright, time for another good update.

Time to wire up the output dc-dc converter. I used some 12 gauge wire I had stripped out of an old car for the leads from the pack to the dc-dc converter.







I found my beefy relay and decided where to mount it.





However, I didn't account for mounting the relay before printing the side panel, so I had to drill and countersink the side plate.





Then it got mounted and wired up.





The handle also finished up printing.





And its mounted up.





And, now for the low voltage disconnect. This is wired to cut power to the relay which is inline with the input power to the dc-dc output converter. So, when the switch is turned off, it cuts power to the low voltage disconnect and the output dc-dc converter for no phantom power draw.

Unfortunately, all of the charging dc-dc converters are still hooked up and will drain the pack somewhat (I think, I should measure that).





And here we have it all mashed together like it will be.

[Daox]

Moar building stuff!

Okay, so its basically done. I got the front panel printed out (10 hours), and it again fits really nicely.









Beefy wires soldered up.







Then disaster struck! As I was assembling it, I started seeing smoke come off of two of the dc-dc charging boards. I had no idea what was going on. Finally, I found out the ac power supplies had popped out of their grooves and were touching. I got that fixed and it seems to still work... but we'll see how long it lasts I guess. As long as the top cover is bolted on, this will not happen again as it holds the two side plates together.





And here it is all buttoned up. I ran out of countersunk screws, but its enough to hold it together for now.





Here we can see that its fairly easy to see the status of the charging. Blue is charging and green is charged.







One little touch was adding feet to it. I wanted rubber, but I had these felt ones on hand...

[Daox]

Alright, I think I've explained how this thing works in bits and pieces but I am going to break it down now that it is all together.

The charging side consists of an five AC power supplies that each put out 12V. Each 12V power supply is wired to a DC-DC buck converter which puts out 4V at a max of 4A. This will charge each parallel string to 4V which is roughly 85% of its capacity or ~2.2Ah. Keeping the charge lower than 100% improves battery life. I've edited the charge curve chart to estimate this below. Charging in this manner should give roughly 320Wh (2.2Ah x 8 parallel cells * 3.6V * 5 series cells).





Now lets take a look at the discharging side of things. Lets start with the power switch. It physically cuts off power to the low voltage disconnect. This eliminates any phantom draw, because the low voltage disconnect powers up an LED display as soon as it is connected. This voltage display is great for checking the state of charge as the max pack voltage is 20V (5s x 4V). However, it does draw something like 200mA when its on and powering the relay.

When you flip the switch on, the low voltage disconnect controls an 80A relay. If the voltage is above its set point, that relay is enabled and power is sent to the output DC-DC converter. As the pack is drained, it eventually hits the low voltage setting and the power to the DC-DC output converter is severed. The low voltage disconnect also has a hysteresis setting which stop the relay from turning on/off as the voltage recovers after the load is removed.

[Daox]

I just measured the phantom draw of the dc-dc charge converters. It is 9mA. With 2600mah batteries and 8 in parallel = 20800 mAh. So, it would take ~95 days to self discharge a fully charged pack. I think I can live with that. The alternative would be to put in relays to physically disconnect the dc-dc converters when the AC power isn't connected.

[Daox]

Also a bummer, I toasted one of my 12V power supplies in the incident I had above. Its only intermittently putting out 12V.

I'm also going to be turning down the charging dc-dc converters max current. 4A is still too high. It smells like warm plastic when the charging goes for a while. I'm hoping they can do 3A at reasonable temperatures. I do not want to add a fan to the enclosure.

[California98Civic]

Wow Daox. Your 3D printing skills have increased a lot with experience. I remember an early project was simply shifter knobs, IIRC.

[Daox]

Thanks! This has been a pretty involved project. But, so far it has turned out really nice.

[California98Civic]

I'd say it's impressive. The basic idea is good: a simple "alt delete" for more recent cars with move complex electronics. Somebody along the way in the thread suggested maybe it is a lot of effort for the gains. Maybe so. But wouldn't you say it is a great project for practicing and developing skills you are interested in?

[Daox]

Thanks. It has been a very fun project.

I think this could be done by someone else. There is no reason you couldn't make this out of wood or something else.

I have ordered a new AC power supply.