Frog Battery Cracks

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Deleted member 4366

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This was mentioned a while ago, but I was reminded while working on my Dahon. This is now the second battery mount that has cracked on this bike, which has suspension front and rear to soften the shocks. I haven't even had to pull this one up, and it was OK less than 100 miles ago. Idoubt that I've done more than a few hundred miles in total. Another good bump and it would have detached completely. It's put me right off frog batteries:


Here's the previous one:

 
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Kudoscycles

Official Trade Member
Apr 15, 2011
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www.kudoscycles.com
Dave....it is a problem with frog style batteries...if you PM your home address I will get Santa to deliver a new bracket. The problem is usually on bikes that are used a lot off-road or when you use the handle at the back of the battery to lift the bike rather than just using it to pull out the battery.
Happy X-mas
KudosDave
 

peerjay56

Esteemed Pedelecer
May 24, 2013
745
199
Nr Ingleton, N. Yorkshire
This was mentioned a while ago, but I was reminded while working on my Dahon. This is now the second battery mount that has cracked on this bike, which has suspension front and rear to soften the shocks. I haven't even had to pull this one up, and it was OK less than 100 miles ago. Idoubt that I've done more than a few hundred miles in total. Another good bump and it would have detached completely. It's put me right off frog batteries:


Here's the previous one:

Would it not be relatively simple to weld a strengthening piece inside the top edge of the bracket? (before the stress builds, rather than after!:))
 

D C

Esteemed Pedelecer
Apr 25, 2013
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Cairngorm National Park
I wonder if the bracket was strengthened it would transfer the stress to the frame and do even more damage. Admittedly mine is a heavier battery, my seat tube cracked from the weight of the battery on a rack attached only to the seat post.
 
D

Deleted member 4366

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It's easy enough to weld up if you have a mig-welder and know how to use it. My warning is more aimed at all the regular guys that buy their bikes from a shop and don't even know how to take the controller out. It would be much easier to buy a bike with a different type of battery.
Frog batteries can break the frame if it's not properly braced. Ones with low cross-bars are the worst. You can improve things a lot by getting an extra long seat pin that goes right down past any bracing, otherwise you get this:

 
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D C

Esteemed Pedelecer
Apr 25, 2013
932
425
Cairngorm National Park
It's easy enough to weld up if you have a mig-welder and know how to use it. My warning is more aimed at all the regular guys that buy their bikes from a shop and don't even know how to take the controller out. It would be much easier to buy a bike with a different type of battery.
Frog batteries can break the frame if it's not properly braced. Ones with low cross-bars are the worst. You can improve things a lot by getting an extra long seat pin that goes right down past any bracing, otherwise you get this:
That's exactly where mine cracked.
I was using a long seat post but that didn't stop it happening though it did prevent it coming apart which would have been a bit nasty.
I've fixed it now by bolting it through.
 

Gdread

Pedelecer
Sep 9, 2012
91
1
Staffordshire
wow, I'm on my third rack now.

Rack one from Greenbike kit snapped at the welds, rack two a cantilever rack fitted on the seat post snapped on a bumped kerb. Rack three appears to be lasting (mounts on the axle).

Whats the best option - Frame bags, dv8eh rack and shoe bag?
 

cwah

Esteemed Pedelecer
Jun 3, 2011
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www.whatonlondon.co.uk
All my seat post rack cracked after few months:
- 2 frogs batteries cracked.
- 2 seat tube mount cracked with 3kg battery althought it was advertised for 10kg charge.

Since then, I never EVER used any seat tube rack on my bikes.
 
D

Deleted member 4366

Guest
There's one cheap seat-post rack that works because it's made of steel. I've been using them on my Giants for over 2 tears with 20aH batteries. one has a Ping LiFePO4 that's very heavy. It's the one in the first photo with criss-cross red elastic on it and that cheap-looking quick release clamp, not the other one. If you search Ebay for it, you should find it rather than this ad, which shows another one.
REAR BIKE RACK FENDER PANNIER MUDGUARD BICYCLE CYCLING BAG CARRIER + REFLECTOR | eBay

If you want a normal rack, make your own like in my DIY rack thread. We've been using these with 20aH batteries too, and never had one fail,
 

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Arbol

Esteemed Pedelecer
Aug 31, 2013
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There's one cheap seat-post rack that works because it's made of steel. I've been using them on my Giants for over 2 tears with 20aH batteries. one has a Ping LiFePO4 that's very heavy. It's the one in the first photo with criss-cross red elastic on it and that cheap-looking quick release clamp, not the other one. If you search Ebay for it, you should find it rather than this ad, which shows another one.
REAR BIKE RACK FENDER PANNIER MUDGUARD BICYCLE CYCLING BAG CARRIER + REFLECTOR | eBay

If you want a normal rack, make your own like in my DIY rack thread. We've been using these with 20aH batteries too, and never had one fail,
Is this one?

http://www.aliexpress.com/store/product/Bicycle-Rear-Rack-Bike-Carrier-Aluminium-Alloy-Panniers-Rack-Fender-Rear-Mud-Guards-Mudguard-Bicycle-Rear/900148_527673483.html
 

Kudoscycles

Official Trade Member
Apr 15, 2011
5,556
5,037
www.kudoscycles.com
There are 2 problems in this thread that really have similar causes and solutions.
1. The frog battery mount will crack where it mates with the seatpost if you incorrectly use the handle on the battery to lift the bike. It will also crack at the same place if you do a lot of rough off-road riding due to the battery being cantilevered on the seat post and having no outboard support.
2. The seat post needs to extend down into the seat tube,beyond the junction of the top tube/rear upper stay/seat tube,ideally by 30mm minimum-but the outside diameter of the seat post is often much smaller than the inside diameter of the seat tube,so the seat post can still float inside the seat tube and cause stress at the point where the seat tube extends above the aforementioned junction-if you look at D8VEH's above photo of failure of the seat tube,this point is obvious.
If you add frog batteries and cantilevered racks this increases the stress at that point.
The solutions are...
1. Fit a rack which is supported onto the rear stay,if possible attach the frog battery to this rack
2. Machine a thin walled sleeve that has an od to fit the id of the seat tube and an id to fit the od of the seat post.,glue this in place.
3. Use the longest seat post available
4. Never extend the seat post such that the lower end of the seat post is above the 'point 30 mm below the junction'and preferably further down in the seat tube.
5. Never pick the back end of the bike up using the handle of the frog battery.
If anyone has damaged their bike like D8VEH's photo,I have designed a solution which I would be pleased to supply..it saves scrapping the frame.
KudosDave
 

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