"Boost" Switch from 36 to 48 volts on a Pedicab?

[pediman]

I just installed on my Pedicab the Golden 901 750w Pro Kit (http://www.goldenmotorusa.com/index.php?pg=hub) powered by a single Golden 36 volt, 16AH Lithium battery ( http://www.goldenmotorusa.com/index.php?pg=batt ).

Overall, I am happy with the system. The speed is more than adequate but I could use a little more power on some of the hills According to Golden, going to their 48 volt Lithium battery would give me 20% more power in the hills. I could also use a little more range.

Because of this I have ordered their 48 volt, 12AH Lithium battery.

Assuming the 20% increase in power from the 48 volt system, my thought was to hook up the two batteries (36 and 48 volt) with a switch accessible while riding. The switch would perform two functions. First, if I ran out of juice, I would simply switch to the other battery on the fly as opposed to having to stop and change batteries. Second, I could use the 36 volt battery most of the time and then switch over to the 48 volt when I encounter a steeper hill. Then swtich back to the 36 volt. Kind of like a "boost" switch. I'm very new to this so I just have the concept but need help in the "how-to" department.

(1) First, is such a system feasible using these two batteries?

(2) Is there a "plug and play" switch like this already on the market that I could hook up easily? If not, exactly what do I do? The manufacturer mentioned I needed an isolator if I was switching between the 36 and 48 volt batteries. Is this part of the switch?

(3) Currently, the 48 volt battery is not available so I may temporarily use a second 36 Volt Lithium battery for just added range. Would I use the same switch or could I use a simpler switch (without isolation) for this setup?

(4) As an alternative to "3" above, could I just hook the two 36 volt, 16AH Lithium batteries in parallel and forgo the switch? The manufacturer said it wasn't a good idea but didn't seem to have a reason why.

(5) As an alternative to the original idea (switching between a 36 volt and 48 volt) could I use a 12 volt Lithium Battery instead of the 48 Volt, then hook it up to the 36 volt in a series arrangement with a switch. That way I could use the 36 volt most of the time and switch to 48 volt power on-the-fly only when I needed it? If this idea was feasible I would probably end up with two 36 volt, 16AH Lithium batteries and a single 12 volt battery.

Thanks for any help.

Richard

 

[Jeremy Harris]

Does the upgrade include a new controller, with a higher current limit? If it doesn't, then it's unlikely to give you much in the way of improved hill climbing, I think.

The general rule is that voltage determines speed, the controller current limit determines torque, all else being equal. If you are happy with the speed you get from 36V, then you don't really need to increase the system voltage, just increase the current to the motor. There are issues that need to be looked at when doing this, such as if the battery can safely deliver a higher current, whether the wiring is up to more current and whether the motor is able to handle the increased current without overheating.

Some controllers can have their current limit increased a bit without running too many risks, others need a fair bit of work to do this without risk of overheating.

The system you propose with a smaller capacity 48V battery will work OK as a speed boost system, increasing your maximum speed when you switch to 48V, but is unlikely to make a massive difference in hill climbing ability. If the Goldenmotor is a particularly high resistance wind (I know little about them) then you may get a modest torque increase from increasing the voltage, but to be honest I wouldn't expect it to make a big improvement.

I'm surprised at the advice from Goldenmotor, as it seems to be at odds with the general principle above. I'd have thought there advice should have been to upgrade the controller to one with a higher current limit and stick with your 36V battery. Advising you to get a higher voltage, lower capacity battery seems odd.

Jeremy

 

[pediman]

My understanding after talking to Golden is that the same controller is used both when running 36 and 48 volts. They also stated I would see an increase in hill-climbing running with the 48 volts, but I have also heard others say what you state, i.e. I will just see an increase in speed which I really don't need. I will of course know for sure when I test the two batteries out on a hill. If no hill climbing increase for the 48 volt unit then I will simply run two 36 volt batteries using a switch.

 

[Jeremy Harris]

If you're going to run two 36V batteries then it's best to not switch the extra battery in as required as a reserve, it's best to run on both batteries all of the time. This will improve the performance of both batteries, by halving the current drawn from each, meaning less voltage sage and longer battery life. Your total range will be slightly greater this way, too.

It may be possible to connect them together in parallel directly, it may not, depending on the BMS design, but you can always connect them together with two high current Schottky diodes, one in each battery +ve lead.

I think the advice from Goldenmotor to not use a second 36V battery in series is sound. It's very unlikely that a 36V controller would accept 72V without blowing, in all probability it only has 63V capacitors inside and at best 75V rated FETs (two 36V batteries hot off charge may be around 80V).

Jeremy

 

[pediman]

Jeremy,

I made a mistake in my original post which I just edited. I was referring to a "parallel" connection with the two 36 volts, not hooking them up in series. Golden's advice was not to hook them up in parallel but to use a switch instead. Maybe your diode idea would make it work.

Still thinking switch because of the "boost" issue (going to 48 volts) , as well as more versatility, and I also thought the switch could function as fast and easy on/off switch when leaving the pedicab unattended. But should I go parallel, where would one get such a diode unit and what is involved in the hook up?

Richard

 

[Samba]

Their controller claims 50A for 24/36/48v.

The battery claims are odd - 60A max for the 36X16AH and only 35A max for the 48x12AH (should be 45A if its built like the 36v).

I'd assume the 12AH battery claim is more accurate and the 16AH is really 46A Max (16/12 * 35a).
36vx50A = 1800W
36vX46A = 1656W
48vX35A = 1680W

Thats enough juice to make 2+HP - but the actual delivered power depends on your speed and the motor's efficiency at that speed.

That 48v shouldn't help because of its amps limit.
A 48v that can deliver more amps could help.
The 36v in parallel may help - depending on whether you are really getting 50A now. It would increase range, increase the battery lifespan since its not pushed near its limits.

Your speed on the hills makes a difference, the voltage changes the motors prefered speeds. But you'd need a good plot of the motor's power and efficiency to predict the effect.

 

[torker]

Upping the voltage should marginally help the hillclimbing. Only because you are upping the total watts. Like Jeremy said more amps is the way to go. Maybe a slight increase on the size of the shunt in the controller. Since you are talking some serious money for another battery have you thought about lacing the motor in a smaller wheel? Maybe 24 inch. You would have to deal with brake mods, unless you have disc. It would be less than a battery though. It would lessen the load on the system a bit and with a slight shunt mod might really "wake" it up.