I lived on / from 12vDC nominal for many years, and still have issues thinking in terms of powering things from ~115vAC. Voltage drop on 12vdc and lead acid batteries Crap cycle life when not truly fully charged promptly after any discharge, made me oversize wires, a habit which has continued even at higher voltages.
When I first got my Junky 7s esk8, I found the 29.4v 40 watt power supply / charger provided, was actually as high as 30.32volts, and I wired up a buck converter to limit this to 29.4v. I also saw when the red light turned green on said charger, it did not cut off output, it only meant the amperage declined from 0.33 to 0.32. It would never shut off, and would happily overcharge, and depend on the battery BMS to prevent this.
I have good 12vdc infrastructure in my garage workshop, and some old but healthy AGMS on my garage floor and decided to just use voltage boosters to charge my ESK8 battery from these AGM’s which I can hold at their ideal float voltage with a manually adjustable 100 amp power supply.
I now basically own almost every 150 watt+ rated booster sold on Amazon or Ebay, with the latest acquisition being Big Red 40 amp/ 1800 watt on the bottom.
The ratings are kind of marketing BS. Some will say maximum output amperage, some will give input amperage limits, some will say maximum wattage. and there are all sorts of dis and mis information regarding their actual capability.
First off is Boosting from 12v nominal to 10S liion charging voltages is a big limiting factor.
The ‘400 watt’ red booster on top, is the least expensive and my least favorite, mainly as the voltage potentiometer is Clock wise to decrease output voltage, CCW to increase, opposite, but the current pot is normal.
The potentiometers are also located on PCB where if one bridges the heatsinks, with a 50MM fan, they become inaccessible with the fan running. I always change output voltage depending on whether I want to charge to 4.1 or 4.2 volts per cell, and always change the amperage depending on if I need to ride ASAP, or in 6 hours. Charge as fast as necessary, as slowly as possible.
I did burn out one 400Red one, asking it for too much juice too, the wire around the toroid turned purple despite a powerful fan blowing over it.
The Blue booster below it became my favorite, even though it just says 150 watts max output. All three potentiometers are normal, and it has a light which one can adjust when it turns from red to green, such as when amperage tapers to less than 0.2, the red light can turn green and it is easy to see at a distance when I need to unplug it. I added a 24vDC fan to it, and when fed 12vdc nominal. It is basically silent, but not enough on its own to keep the booster cool, at 150 watts output
I was using this booster from a 5s power tool battery to portable recharge in the park, and also from my 7s2p premade battery, but the 150 watts maximum rating was the limiting factor whether fed 5s or 7S voltages, and while adequate, I wanted the ability to charge faster. the 24v fan at these higher input voltages was quite effective in keeping it cool.
The White booster claims 600 watts, but this is only possible if boosting from a much higher voltage. From 12v Nominal, I can get about 170 watts without it getting too hot which for me is about 75C, even though electronicas can likely handle more.
One needs to attach it to a heatsink, and drilling and tapping the heatsink is a pain in the keester. I used my 7s2p enclosure and battery to make a portable charger setup using this booster, attached to a thick plate of aluminum which was attached to a finned heatsink. I can reliably charge at 250 watts, but my 7s2p premade battery is only 104 watt hours.
The white booster will have a big old spark when connecting it even to 12vdc, So I put an XT90S on its input.( use an Antispark switch in 7s enclosure) It has a 15 amp fuse on the input, which I blew when testing it on 12vdc input.
It refused to be removed and replaced with a wire, So I bridged it with solid 14AWG and added an Inline ATC fuse on the 10AWG input wire.
Both potentiometers are backwards, and at 42v, are super difficult to dial in say 41.8v, or 41.12, or 42v precisely. At 170 watts with a nearby fan blowing over and under the heatsink it was still getting quite warm at 12v nominal input so was kind of bummed at the effort spent to turn this booster into my new benchtop from 12vdc nominal booster.
I honestly do not need to charge above 150 watts very often, but when I do, I am impatient. My charge port and BMS are rated for 10 amps and I wanted to be able to approach this, on the bench, from 12vdc nominal.
So I ordered Big red 1800. Last night I tried to find its maximum, assuming the heating would be the limiting factor. It has a temp sensor resting on heatsink, and a fan. I first tried it using a 6S1P 50E battery that I made for my TS101. Long story short I kept having to reduce the current potentiometer to keep the cells below 9.8 amps output, and they still reached 58.8C well before the BMS would have cut them off. Big red’s fan was just starting to cycle on and off, and felt only warm to my touch.
i then tried it with 12v nominal input. Big red has a third potentiometer, that is supposed to allow one to set a minimum voltage for protecting input battery. i had to fiddle with this pot in order to get more than 165 watts out of the booster. I did manage to get 9 amps output, which was about 36 amps input, and the input wattmeter was saying 12.22v. I could not get more than 9 amps from this no matter how much more I dialed up the current potentiometer, and output voltage was set to 42v. It did get quite warm and the fan was running continuously.
9 Amps is a 1 C charge rate for my BAK45D 10s2P, and close enough to the 10 amp max of my charge port and BMS that I find it acceptable.
It was turning 50 to 60 watts of power into heat though, at that output level.
I don’t expect to often dial up the charge rate to this level, and the unit itself is big enough that I doubt it will ever find its way into a backpack or Fiona’s chariot to be part of a portable charger.
Since I made the BAK45D 10s2P I rarely have needed more range, so the portable charger factor is not as necessary as it was with my old DMEGC102P.
That battery would just get way too hot, So portable charging at 150 watts in hot Florida was a bad idea, but it was nice to leave the park at near full charge and have more torque on hand.
I am infected with range brain, even though I don’t need more range.
I would however explore further a field if I knew I could easily make it home.
The DMEGC 10s2p in my mini’s enclosure connected in parallel to BAK45D10s2P through charge port is likely the best method of range extension, as opposed to a portable charging source, but I like to have the ‘what if’s’ covered.
The Samsung 50E 6s1P flatpack, and the white booster can fit in my cargo short pocket and should be good for 160 watt rate of charging and return me about 3 miles of range towing Fiona at 18 - 20MPH.
I can load her chariot with all sorts of emergency range 2, 5 and 7S batteries for portable charging if needed, but will I ever need?
I hope her health holds. Rolling with my best friend ever is basically my only Joy these days.
Should take her out on the Kayak soon too.
Gonna go hit up the park right now with her.
