Ultracap Bike

[317537]

Do a little test.

charge a single cap to power a few led lights and put them on straight and you will see the caps discharge too fast. Add a 1/4 watt resistor to limit the current and you have a light that burns for hours.

Caps for batteries find inefficiency in electronic components and can provide as much current as the component will waist. If the cap can feed inefficiency, as in the led light example, it will. The current peaks could even damage components in some situations. Regen can be chaotic on your fets and adding straight caps over terminals with out current limiters between regen scares me.

Ultra caps leads and terminals are the limiting factor. In audio applications the caps can charge and discharge so fast the terminals all ways fail so they need special engineering to by pass this effect. I do not see terminal failing in EV applications but I do see related issues arising when dealing with big RAW caps straight onto terminals.

Edit.

The surface area of the any cap can absorb much power and to charge a cap as fast as it can be charge you would need lead and terminals that equal the plates surface areas or else heat would be the issue.

Sharing current path ways between the caps and cells through a resistor inside the battery terminals is not an issue. Just so you know I do not plan on limiting the the current outside any batteries cells or terminals.

Running a controller feed for an Ebike through resistors is silly and this is not what I mean.

 

[317537]

There also appears an issue with balancing over a series capacitor too, identical value large value resistors over each cap at 1/2 watt should make the voltage divide stable.

 

[317537]

The internal resistance vs inductance of a capacitor over shoots both batteries internal resistance and inductance.. Most of the available current from regen would direct it self into the capacitors before the battery.

To some degree the battery would soak up any energy at a rate beyond any use for charging. At the same time its not all about providing the all the current to recharge batteries you would want the energy to be used straight off the caps. A balance needs to be sorted IMO. Even with lithium batteries the more farad and available caps by wiring them in parallel could create issues. Lithium is a lot better at soaking up regen and provide more reservoir at any given time for both regen and caps to be useful. However to a different extent similar benefits should exist for SLA's if you approach it correctly.

I would be guessing that the OP's cap bank has current limitation through solid state regulation at the output anyway.

 

[JCG]

I would be guessing that the OP's cap bank has current limitation through solid state regulation at the output anyway.

Unfortunately, I don't have anything like that. These are good thoughts here, because I'm about to be trying another small (2.5 Ah)battery pack (44 V NiMH) to put in parallel with the 48 V cap module. I'm paying attention to a couple of things that I didn't check in to when I used the DeWalt pack in parallel: capacitor leakage at different voltages, and keeping a close eye on what currents will be allowed in exchange between the cap and the battery while in operation.

I've installed a couple of switches, one to disconnect the battery from the cap so that it won't be dumping current into the cap overnight (or over whatever period of time) as the cap leaks. At 44 V, the cap is self-discharging at around 23 mA which is a problem. I'm not sure if this is also a problem with the newer modules, but I'll test them for leakage this week. The second switch breaks the six NiMH packs from series into three sets of two in parallel for charging.

The cap-battery current that worries me during parallel operation is kind of the opposite that you're considering. I imagine starting the commute with a battery and capacitor both at 44 V, with a 23 mA leak. Then, I start to motor around. The cap is the first thing to provide the current needed, which drops its voltage and causes the battery to try and dump current into it due to the new delta V that it sees between it and the cap. But, with even a volt's difference, this current can be really high and could damage the battery by discharging it too fast. Before, I was using regen and pedaling against generator resistance to keep the cap voltage within a given range to protect the battery in both directions. I'm not as worried about charging the battery too fast, since I'd just try to keep the capacitor at or below the constant voltage level used for charging the battery pack in question (for NiMH, around 1.45 V/cell).

Like you guys mentioned, a resistor could stem the current quite a bit (I'd probably use that light bulb I talked about in a previous thread, since it effectively limits current through it to around 2 A, which would be OK for the batteries), but I don't like wasting all that power. Some kind of active current-limiting circuit would be great...

 

[wineboyrider]

BUMP!

 

[mat h physics]

Re Bump!