One of the first problems a new E-biker who wants to add a kit to their bicycle has to figure out is…Where do I mount the battery, and how? This article will help you see what the common methods are, and hopefully to help you decide what would work best for you.
Remember the ebike battery is the most expensive component in almost every ebike and also the most fragile. Which ever method you choose for mounting your battery, remember to use great care. Treat your battery like a carton of fresh eggs…and mount it with plenty of support and padding so that your cells do not become physically damaged. Ruining a few cells can ruin an entire pack. Never charge a damaged battery pack.
Rear Cargo Rack
Mounting the battery on a rear cargo rack is a frequently used method on the most affordable kits. We don’t like them because they make the bike handle odd at the higher speeds, and if you use a common rear hub…most of the E-bikes weight is then located in the back. That makes the E-bike very awkward to lift and move around.
If you are using a large and very heavy Sealed Lead Acid (SLA) pack, the rear rack is often the only place that will fit, but…that is also the absolute worst place to put a large and heavy pack; high up and at the very rear.
If this is for a kit, the cargo rack is usually the type that bolts onto your bike frame. These bolt-on cargo racks are usually too weak for the job they are given, and the bolts often work their way loose and squeak. Some factory turn-key E-bikes have a heavy-duty welded-on rack for a battery. For those, we still don’t like where the weight is located, but at least they are strong and don’t come loose.
The absolute best place to locate the weight of a battery is as close to the center of the frame as you can, and as low as possible. One of the most frequent methods we’ve seen over the last two years to do this has been to use a triangle bag. If you have a hard-tail frame, you probably have a large triangle space, and that means you have a variety of affordable options when it comes to a triangle bag.
Here is where we recommend to buy affordable quality triangle bags made here in the USA: Luna Cycles
Water Bottle Mount Cylinder
When you Google “water bottle battery”, this is the type that comes up. It is a cylinder that holds 42 of the popular 18650-format cells. This limits either the voltage or the range, but it easily attaches to a frame adaptation rail that is bolted to the common 2-bolt water bottle attachment points. The range is dependent on the particular cell that is chosen.
If you choose the 48V version of this pack, the number of Amp-hours (AH) can vary from 8-Ah up to 11-Ah. However, if you choose the 36V configuration (with the number of cells being fixed), having fewer cells that are configured in series means that more of them can be configured in the parallel groups. A 36V pack (as opposed to the same size pack at 48V) can have as much as 15-Ah, if a high-Ah per cell model is used.
This aluminum hard case also mounts to the water-bottle attachment points that are now common on bicycle frames. In fact, in this picture you can see the second set of “2-bolt” water bottle attachment points on the seat-tube. Since the desirable 18650-format cells (cylindrical, 18mm diameter, 65mm long) can easily fit sideways between a riders legs without interfering with pedaling, this 80mm wide (3.2-inches) case is becoming VERY common.
This type of case holds 50 of the 18650’s, and to give you an idea of what’s possible…if you buy one of these cases from em3ev.com, and select the Samsung 29E cell (2900-mAh per cell), the 36V version can hold 16.5-Ah of range. Also, next year in 2016 there will be cells available to the public with as much as 3500-mAh per cell, meaning 20% more range with no other changes.
Top tube saddle case
Some builders have purchased cargo cases from bicycle sites that sit over the top-tube of the frame, with some storage space on either side. Kinaye Motorsports (shown below) puts their brick-shaped LiPo battery packs in a square-ish and affordable saddle-bag, and others who wanted even more volume have purchased a larger (and much more expensive) saddle-case from the German company Additive.
Builders who like these, often have frames with the rear shock absorber located inside the bicycles frame triangle. They also often have a small triangle space, which doesn’t leave many options for battery placement.
Front Cargo Rack
The pic below may look a little front-heavy, but many builders have recently tried this, and its not bad when you are using a large and heavy rear hub, like the Cromotor, the MXUS, or QS. With the overall weight of this E-bike polarised (half in the front, half in the back) it handles fairly well. Not as good as having a central battery and a mid-drive on an off-roader, but it actually isn’t bad…especially for a street bike.
The bike is a 2005 Giant DH Comp from endless-sphere.com forum member “Ohbse” in Aukland, New Zealand. The fork is the well-regarded Marzocchi 888 CR. The box is a Pelican brand, and he found the mounting clamps by searching Ebay for “Accessory Clamp 1.375-inch ID”. The clamps can be found for roughly $15 each. If you can’t find a clamp that is the exact ID of your stanchions, get ones that are larger and just shim them to fit with curved copper sheets made from copper tubing from a plumbing supply.
Our friend Miles uses a backpack for his lightweight eMoulton, and he does that to make this short and light commuter easier to carry into his work and back to the street. Very few riders do this, but it does completely free up the rider to use any frame they like without having to find a way to attach the battery in a secure way.
For builders who ride over 28-MPH, it is highly recommended to use a full-suspension frame, but…that also means that there is usually a shock absorber in the middle of the frame triangle (for most full-sus styles), which clearly makes it difficult to mount a battery anywhere.
Another benefit is that…in the very rare instance that the battery gets so hot that it starts smoking…it is easy to come to stop and dump the backpack, which prevents any damage to the rest of your expensive E-bike from a LiPo fire.
The battery is often the most expensive part of your E-bike system, and sadly…they are occasionally stolen. With a backpack battery, you will likely never forget to take the expensive battery with you, whether you are going into your home, a cafe, or some store.
Plus…if the controller or throttle freezes in the “ON” position (and won’t stop), all you have to do is bail out, and the battery will disconnect automatically when the connectors on the power cable pulls apart.
The pic below is courtesy of our friend Karl Gesslein from electric-fatbike.com
Written by Ron/spinningmagnets, June 2015