Giant second battery install advise sort

[Baz the balloon man]

Hi Guys.

In previous posts I said I had a Giant Prime Hybrid it’s an older bike with the Yamaha PW Motor.

Then the wife has now got the Giant Fast Road E +1 with the latest Canbus charger needed which I still not have been able to get a decent S/H one.

Please see attached the photos of the Two Giant battery’s.

Struggling to sell the Prime it’s a good bike if you like this style of frame . Which she has been using to deliver small parcels up to the Evri shop.

I am wondering if I can put the Battery from the prime as a Second battery on the Fast Road E1 so to give the bike a very good range.

As it’s a rear mount battery they are both 36v and both Giant .

Can this work if I wire into the loom after the discharge port ?

would either battery be damaged by this set up ?.

If it can work will I be able to just charge with my standard giant charger through the rear mounted battery assuming that once charged the down tube battery will then take its charge sort of in reverse from the rear rack battery.

SO I would not have to get the second Giant smart charger.

This is for our own use and not for sale.

CHEERS

BAZ

 

[matthewslack]

A very complicated way to avoid buying a battery charger!

The charging aspect will not work safely because that 'backdoor' bypasses the BMS.

Connecting the two batteries in a way the manufacturer did not intend is also likely to be problematic. If both are CANBus chances are it will confuse the system when two batteries are detected, and either one will not turn on and so might as well not be there, or both might not turn on, so the bike won't work at all.

Two batteries that fit the bike is the straight forward way to get more range, and a new charger if a second hand one is not available is the way to charge.

 

[Baz the balloon man]

A very complicated way to avoid buying a battery charger!

The charging aspect will not work safely because that 'backdoor' bypasses the BMS.

Connecting the two batteries in a way the manufacturer did not intend is also likely to be problematic. If both are CANBus chances are it will confuse the system when two batteries are detected, and either one will not turn on and so might as well not be there, or both might not turn on, so the bike won't work at all.

Two batteries that fit the bike is the straight forward way to get more range, and a new charger if a second hand one is not available is the way to charge.

Thanks Mathew.

So what you are saying is a battery sending charge through the back door , even if any electronic handshakes are in place between the main battery and controller are in effect bypassing the safety system of the BMS of the battery that is receiving the charge making it liable for over charging and being damaged or worse ?

I will sack this idear , it was not to avoid buying the charger just thought I might be able to do a work around as both are Giant batteries.

The wife will just go to Giant and buy a new charger .

Going back to fitting Two battery’s on a bike which is also something I am planing on a Carrera /Yose conversion for myself again initially but after watching Panorama last night regarding e bikes I can see the need for very long range road legal bikes people trying to make a living Or ditching the cars.


I have a HL down tube and intend to put a rear rack on too.

So what we are saying is it’s ok to do ? But we should charge each battery individually?

Do we also need to have any other compatibility other than the same voltage and batteries that have a standard BMS .

Should they have the same AH and the same brand and voltage cells ?

 

[soundwave]

if you need to ask id not bother with 2 batts yes it can be done but!

if one batt is lower than the other one then this can go bang esp if you put a flat batt on a fully charged one so they need to both be fully charged and drained at the same time and be within of 0.2-0.5 fully charged to then connect them together as 1 batt.

if you use say 1 batt all week and then use both for longer trips one batt will degrade faster than the other and over years get well out of whack as will only be as good as the first batt to fail when the other can have some left.

and sparks flying when connecting the 2 together and if the voltage is mismatched ie one charged and 1 flat it will dump 20A in to the flat batt in one hit so not ideal if not checking them with a multimeter and a dumb bms

 

[Cadence]

I have two identical Yosepower 36v. 13Ah. batteries. One is 18months older than the other, but still holds a full charge. I alternate them for normal use. For my "long distance" hybrid I have one mounted in the usual downtube position providing the power and the other is mounted on a rear rack using the downtube slider bracket, but is not connected to anything:-



The idea is to stop when the first battery is getting low and just swap them over. I haven't done a long enough distance yet to fully deplete both batteries ( and wouldn't run them right down anyway), but would expect do at least 65 miles. I have done a 45 mile trip and swapped them half way. Compared to a 30+ ride using just one battery the voltage drop on hills was considerably less.
There are connector leads available (Topbikekit etc.) to connect two different-style batteries of the same voltage, but I can't see the point. In that case it would be easy just to use XT60 connectors and swap the feed over manually during the ride. I now have KT controllers that automatically recognise 36v. or 48v., so at some point I will be buying a 48v. battery and will use XT 60 connectors with one battery on the downtube and the other on a rack. Again, the connection will be changed manually. It's simple and foolproof - even for me.
I wouldn't even contemplate trying to charge two batteries from one charger - it seems like a recipe for a fire!

 

[matthewslack]

if you need to ask id not bother with 2 batts yes it can be done but!

if one batt is lower than the other one then this can go bang esp if you put a flat batt on a fully charged one so they need to both be fully charged and drained at the same time and be within of 0.2-0.5 fully charged to then connect them together as 1 batt.

if you use say 1 batt all week and then use both for longer trips one batt will degrade faster than the other and over years get well out of whack as will only be as good as the first batt to fail when the other can have some left.

and sparks flying when connecting the 2 together and if the voltage is mismatched ie one charged and 1 flat it will dump 20A in to the flat batt in one hit so not ideal if not checking them with a multimeter and a dumb bms

There are ways of using multiple batteries connected at the same time, but you wouldn't choose that route unless there is a real need. Much simpler and inherently safer to carry extra batteries for more range but only connect one at a time.

In the simple 'generic' world, you can buy devices that allow two or three batteries to be safely combined on the bike, but you charge each one separately.

In the CANBus world, do what the manufacturer allows and expects.

My main bike is Shimano, and I just carry a second identical battery for range, and on multi day trips, I carry two 4.6A chargers, so two hours charging per day, with both on charge, keeps me going as far as I want to ride in a day.

Bosch have the ability to have two batteries active at the same time. Some cargo bikes use this setup.

I don't know what Yamaha and Giant can do, but I do know of a Momentum cargo bike that is I think Yamaha, with one downtube battery, and a lockable storage box for a spare.

The issue with charging not through the charge port, and so without BMS involvement is basically what you had happen with that battery before Christmas: full 42V across the cell pack but no balancing and no sensing of individual cell groups. An out of balance pack can allow one cell group to exceed its maximum voltage before the whole pack reaches 42V with undesirable results.