possible to charge bike battery with large external battery pack? while riding?

[melk]

Hi all, new member. I've put about 500 miles on my Rad Mini since April.

I'm wondering if it's possible to charge my stock battery with an external battery pack, while I ride?

Seems like it might not be possible or a good idea for the battery, even if it would technically work?

Here's the specs of each:

Jackery Explorer:
240 watt-hour (16Ah, 14V) lithium-ion battery pack
AC outlet (110V 200W, 400W peak)
---------------------
My stock radmini battery:
672 watt-hour (14Ah, 48V) lithium-ion

I happen to already have this model Jackery. 200W output is not much but they do sell larger models (at corresponding high prices)

I would hope the controller should be smart enough to not allow any damage to the battery or controller, but I just don't know enough.

 

[RunForTheHills]

Sort of. You can't charge a 48V battery with a 14V battery. It is possible to connect two batteries of the same voltage in parallel. You have to make sure they have the same voltage level (SOC) when you connect them together otherwise there could be a current rush between the batteries as they try to equalize the charge.

 

[indianajo]

Possible with a new 48 v battery, but not wise. There are chemical events involved with discharging & recharging that are inefficient. I wouldn't connect (switch on) the auxillary battery until the first one was run downl that involves a diode preventing charging of the original battery, a switch, or a 30 A rated connector to change from one to the other.
Getting into the wiring to splice the spare bat port would be difficult since Rad has hidden wiring. And cutting a splice point would void your warrenty. Kind of a risky business anyway, 30 A connections are not easily made by inexperienced people. Controllers don't come with 2 sets of battery input wiring.
Really, more sensible, buy a spare battery from rad and carry it in a bag. Then when you run down the first, change them out.
The battery looks like a high volume case, you may be able to find other sources of batteries that fit. See parts & accessories forum. Warning, I bought 2 dud batteries, one from amazon, one from ebay, got the money back for only one. A 5 star amazon or ebay rating means nothing when customers don't test the product fully before they rate it.
672 watthour battery is not tiny. My original working 840 wh battery is large enough, my hips are giving me pain before the battery runs out. I'm ready for an easy chair after 5 hours on the bike. The rad mini has a geared hub motor that you can pedal without drag after you run down the battery.

 

[melk]

I need to study up as I have only the slightest understanding of electricity, let alone battery chemistry.

I don't want to fry anything but there is physically nothing preventing me from using the stock AC charger plugged into the battery pack.

The unit outputs normal AC (up to 400 W peak, but let's not get hung up on the number, you can get stronger units that output up to 1000 W sustained or more)

I thought the 'brick' of the bike charger does the conversion to the volts/amps it needs to charge the battery.

I assumed, and maybe this is my flaw in thinking, that the AC being fed by the portable battery unit is essentially the same as from a house wall outlet?

So it's not so much a question of would it charge, which I believe to be true, but rather, what's going on in a lithium ion battery during charge/discharge cycles and is it safe to even attempt such a thing (gut feeling says NO)

 

[RunForTheHills]

I am not sure what you are saying. The output voltage of a 48V charger should be around 58.8V DC and the SOC of the fully charged battery will be 54.6V. The charger will regulate current. The maximum charging current will depend on the C rate of your particular battery, but a slower charging rate is better for the battery.

 

[RunForTheHills]

The AC charger for your battery contains a transformer to reduce the voltage from your outlet to the charging voltage and also circuitry to convert the AC (alternating current) to DC (direct current).

 

[indianajo]

The charger on the rad mini doesn't produce AC anything. It converts 120 vac wall plug voltage to up to 54.6 volts DC.
You can power the charger on the Rad mini with a 120 vac inverter. You could power a 12 vdc input ac inverter with a 14 v battery. Very inefficient. you lose about 40% of energy in the charger and another 50% of energy in the inverter. Plus, my brother that buys inverters for his work, says 99% of them are garbage and last just a few days. He buys his inverters at the big truck stop, Pilot.
Plus in the rain, the 120 vac wiring is subject to shorting to the frame & shocking you. Plus commercial 120 vac inverters are designed to be inside the truck, not outside in the rain. I don't expect one would last long at all in the rain.
Happy riding & shopping.

 

[6zfshdb]

Before I spent money on a larger Jackery Explorer, I'd consider getting a second Rad battery instead. In addition to the inefficiency, there is also a size and weight consideration in carrying the Jackery and your charger on the bike.

 

[RunForTheHills]

Ah! The Jackery Exlorer has an inverter built into it. Yeah, It would probably work with a 2A charger, but I wouldn't carry that thing on my bike.

 

[rich c]

There are endless ideas ranging from solar panels to gas generators on the bike or trailer for charging a stock battery. All of them are pricey and never as lightweight nor easier than just plugging in a 2nd battery when the first one gets low.

 

[retiredNH]

The voltages and currents involved here are impressive, and dangerous. If you don't know electricity, wiring and safe electrical practices cold, (and you say you don't), then shelve the idea immediately.

I should add that using a 240 watt hour battery to charge a 672 watt hour battery doesn't add up, especially when you consider the inefficiencies of converting voltage to something useful. You're looking at a lot of work (and risk) to gain a few percent in range. Example: Let's be optimistic and say your Explorer battery can charge your radmini battery at 50% efficiency. That means you've added 120 watt hours to your battery, or about 18% to your range. In real life, it will be much less.

 

[m@Robertson]

You could take that Jackery, connect an ebike charger to its AC output, and charge the battery thru the inverter on the Jackery so long as your watt/amp draw on the charger is compatible. Yes it will work just fine.

With that said, it would be a horrible idea as there would be enormous losses in more than one kind of efficiency. It makes vastly more sense to buy another battery, or carry along a charger and stop for a sandwich and plug into something while munching. Probably the Jackery is something you already own so you don't want to have to spend more money. Sorry bud wrong tool for the job.

Here is my 2000wh SoGen in the cargo hold of my Bullitt. This 60+ lb monster was there only to be transported home after Amazon delivered it to my office. Its battery is smaller than the one built into the bike and the SoGen as a package weighs like triple that battery. One of its uses IS to charge up my trails bike from a campsite (along with folding solar panels... that weigh 14lbs x 3) but I sure don't ever intend on carrying it along with me ever again.

 

[harryS]

I would estimate that your fully charged Jackery sitting on your ebike, running your charger plugged into the battery will probably give you 150WH at best. and maybe 25% more range. That assumes you have the typical 2A charger, and it will run about 90 minutes before it runs the Jackery flat.

.

 

[retiredNH]

I would estimate that your fully charged Jackery sitting on your ebike, running your charger plugged into the battery will probably give you 150WH at best. and maybe 25% more range. That assumes you have the typical 2A charger, and it will run about 90 minutes before it runs the Jackery flat.

.

Your estimate is way high. See above.

 

[harryS]

Your estimate is way high. See above.

Maybe. I derated the 250WH spec of his Jackery down to 200WH actual, and knocked 25% more for losses, converting to 115AC and back to 54.6V at the charger for a net 150WH. Then I figured the actual WH of the Rad to be 600, and that;s how I got 25%, 150WH on top of 600WH. Feel free to tell me where I'm off here.

I'd like to see him try it anyway. I don't see why he can't transfer 100 WH into his bike. That's one hour of charging with your typical 2A charger.

 

[retiredNH]

Maybe. I derated the 250WH spec of his Jackery down to 200WH actual, and knocked 25% more for losses, converting to 115AC and back to 54.6V at the charger for a net 150WH. Then I figured the actual WH of the Rad to be 600, and that;s how I got 25%, 150WH on top of 600WH. Feel free to tell me where I'm off here.

I'd like to see him try it anyway. I don't see why he can't transfer 100 WH into his bike. That's one hour of charging with your typical 2A charger.

Your estimate of losses is way low. You have multiple sets of conversion losses: conversion from battery voltage to 110v AC; conversion of 110v to charging voltage and rectification to DC; charging the battery. Data that I could find points to each of these steps having an efficiency of 80 percent or so. Sounds great, but the overall efficiency is the product of each: 0.8 X 0.8 X 0.8 = 0.512 or about 51% efficiency. So you only get about 1/2 of the power into the battery, and that assumes you have good components along the way. OTOH, it's relatively easy to use a cheaper component (AC adapter, charger, battery) with an even lower efficiency.

 

[m@Robertson]

Add to the above its not free to carry all that extra weight. Some loss of range will occur there as well.

 

[harryS]

So you only get about 1/2 of the power into the battery, and that assumes you have good components along the way. OTOH, it's relatively easy to use a cheaper component (AC adapter, charger, battery) with an even lower efficiency.

I gave him 150wh out of the Jackery. You're giving him 120 wh at 50%, We're talking about 2-3 miles difference in prediction. I still think it would be fun for melk to test them out.. That way, he's walking home and not me or you.

A similar question came up some time ago, and the gal insisted to the many detractors that she had done it, etc, but never posted details.

 

[BrianK]

I have a Yeti Goal Zero Lithium 1000ah battery with usb, 12v and 120v outlets. I could put it in a trailer to recharge my battery via the standard charger, but it’s heavy and moderately bulky and I’m not sure just how much it would extend actual ebike battery life. I run a BBS02 fat tire bike and use a dual battery parallel wire to run a 48v 10.4 ah and a 48v 20ah battery.

 

[RunForTheHills]

I have a Yeti Goal Zero Lithium 1000ah battery with usb, 12v and 120v outlets. I could put it in a trailer to recharge my battery via the standard charger, but it’s heavy and moderately bulky and I’m not sure just how much it would extend actual ebike battery life.

Yeah, but how much would hauling that thing around on a trailer suck the fun out of your bike ride? The specs say that it weighs 40lbs. A second 10-15lb battery would double your range and you could carry it in a pannier. I guess if you already have the trailer, you could try it.