Mixing Batteries with Different AH Values

[E-Moto Tuner]

For testing purposes, it ok to mix batteries with different ah values?

Mix would be 2 12v 32ah, 2 12v 20ah, and 2 12v 18ah for testing a 72v ebike.

 

[From-A-To-B]

If you’re just hooking six 12V batteries up to create 72V for you to power up your set up, it’s probably fine. I wouldn’t take a machine for a ride with that hodge podge of batteries. Note that some BMSs don’t like to be in series like that. So if these are lithium batteries, you might check in on your BMSs.

For testing purposes, it ok to mix batteries with different ah values?

Mix would be 2 12v 32ah, 2 12v 20ah, and 2 12v 18ah for testing a 72v ebike.

Lastly, wire in an in-line fuse of very low amperage so if something goes wrong, you lose a fuse rather than components.

 

[amberwolf]

For testing purposes, it ok to mix batteries with different ah values?

Mix would be 2 12v 32ah, 2 12v 20ah, and 2 12v 18ah for testing a 72v ebike.

Depends on what you are testing, how you hook them up, and what you need out of them to get the testing done.

As noted above, if they have BMS they may not be seriesable.

If they are SLA they are seriesable.

 

[E-Moto Tuner]

Batteries are lead acid, its a project e-moto that I'm rebuilding, just want to hook up the controller, hub motor, throttle and everything to test it on the stand.

What amperage inline fuse would be sufficient? Controller is 70a, hub motor is 3k.

 

[From-A-To-B]

Batteries are lead acid, its a project e-moto that I'm rebuilding, just want to hook up the controller, hub motor, throttle and everything to test it on the stand.

What amperage inline fuse would be sufficient? Controller is 70a, hub motor is 3k.

A 5amp fuse will allow you to power everything on and spin up your motor. A full throttle, no-load wheel spin might pop a 5A fuse if it’s a fast-blow fuse.

 

[E-HP]

For testing purposes, it ok to mix batteries with different ah values?

Mix would be 2 12v 32ah, 2 12v 20ah, and 2 12v 18ah for testing a 72v ebike.

Assuming the capacities are accurate, then charge them all up and actively monitor the 18Ah battery voltages and don't discharge at a higher rate than the 18Ah batteries are capable of.

 

[E-Moto Tuner]

Used an inline car fuse holder with 12gauge wire and a 7.5a blade fuse as I didn't have a 5a fuse, testing worked fine.

Is it recommended to keep an inline fuse in a 72v lead acid battery setup or is the circuit breaker good enough? If so, would think a fuse matching the amp output of the controller would be the one to use?

 

[E-HP]

Is it recommended to keep an inline fuse in a 72v lead acid battery setup or is the circuit breaker good enough?

As long as the breaker is a DC circuit breaker, you could use either. If not, it won't trip under a fault condition.

 

[amberwolf]

Used an inline car fuse holder with 12gauge wire and a 7.5a blade fuse as I didn't have a 5a fuse, testing worked fine.

Is it recommended to keep an inline fuse in a 72v lead acid battery setup or is the circuit breaker good enough? If so, would think a fuse matching the amp output of the controller would be the one to use?

Depends on what you want it to do.

You would need to look at the spec sheet from the manufacturer of the fuse and the breaker to see when they will trip or blow, since they dont' just trip/blow at the rating on there. They do so after a certain amount of time at a certain amount of current, so they provide a graph or chart to show you how long it takes at how much current for a particular model number, then you pick the rating version of that model to match your needs.

The protection device must also be rated for a higher voltage than the system actually uses, or it probably won't be able to break the arc and can start a fire at the arc point instead of protecting the system against a fire. For example, using a nominally 12v rated fuse in a 72v system has a good chance of not being able to protect it, because the fuse will blow, but the voltage can continue arcing (exactly like a welder) across the open space inside the fuse until it sets fire to the fuse casing or the fuse holder or whatever is close enough to the arc heat to ignite.


If you want to protect wiring you can use normal or slow-blow fuses or breakers rated such that they protect the wires from damage.

To protect electronics you choose fast-reacting fuses or breakers such that they protect well below the limits of the electronics.

If you need both types of protection, you use both types.


Note that the fuse holder itself will greatly affect how the fuse does it's job (or if it will at all under your conditions), and the higher the current and the less airflow on the holder the more likely the holder will deform and begin to fail to make a good connection, which can cause failure of the connection and shutdown of system, or even arcing and fire.

 

[E-Moto Tuner]

Here's pics of the breaker and inline fuse holder :

 

[amberwolf]

You should look up the specs for the breaker. If it is an AC only breaker as implied by the 240V~ marking, it probably won't correctly break a DC overcurrent (can continue arcing across the gap and start a fire inside the breaker, aside from not stopping current flow in the circuit).

The spec sheet will also tell you if it will actually stop the overcurrent you need it to (whatever it is you want it to protect; you have to decide which of the several things it can be setup to do that it is actually going to do).

Same thing for the fuse, and it's holder. (if there are no specs for them you can look up similar fuses by Bussman or other manufacturers of them and guess that the specs should be similar for the same fuse rating)

 

[E-Moto Tuner]

Couldn't find specs for the breaker, but saw similar "DZ47-100 breakers that were advertised as DC breakers with a 230/400v marking on them.

The inline fuse holder has "600v 3a 12gauge" written on the wiring. Thru testing it didn't blow, and charged the SLA battery pack for 8hrs and it fully charged. Next day when turning the key on the gauge came on a second then it went blank. Checked the fuse and it was blown. Put a regular battery jumper wire in its place and everything works fine.

One strange thing with the battery pack is when measuring each battery with a multimeter it shows them fully charged but when measuring the whole pack at the positive and negative that goes to controller it wouldn't read - expected it to read the 82v the gauge display shows but it only showed a horizontal line on the multimeter.

 

[amberwolf]

Couldn't find specs for the breaker, but saw similar "DZ47-100 breakers that were advertised as DC breakers with a 230/400v marking on them.

Be careful about that, because sellers often don't understand the electrical specifications of their products, and believe that DC and AC are interchangeable, when they are not, especially on products like breakers (which are designed differently inside for each of these. The gap between contacts for AC is usually smaller than DC, so an AC breaker can continue arcing when popped and start a fire, while the DC one wouldn't. Some DC breakers also have a special circuit that creates a magnetic field to extinguish the arc.).

I've seen places selling AC breakers for use in DC applications, but they may not operate as required this way. They *may* work, but they might not. You'd have to test it in your type of application, causing a continuous overcurrent to trip it, to see if it works or not.

A google image search for the number you specify above finds this page

DZ47 - 100 Miniature Circuit Breaker: High - Quality Electrical Protection Solution.

The DZ47 - 100 Miniature Circuit Breaker is a crucial electrical component. It is designed with high - quality materials and advanced technology. This miniature circuit breaker offers reliable protection for electrical circuits in various applications. It can effectively prevent over - current...

www.andeligroup.com

which state it's for 50hz 230V AC single pole, or 400v 2, 3, or 4 poles.

There are breakers that look like yours that *do* work with DC, such as those from solar applications; you'd just need to make sure it will work with the

The inline fuse holder has "600v 3a 12gauge" written on the wiring.

That just means the *wire* is capable of that (wire is often marked with it's capabilities). It doesn't tell you what the fuse holder itself can handle, or what the fuse can.

Those knds of blade fuses are generally intended for 12v applications, and probably have a limit of 20-30v for what they are guaranteed to break a circuit of.

One strange thing with the battery pack is when measuring each battery with a multimeter it shows them fully charged but when measuring the whole pack at the positive and negative that goes to controller it wouldn't read - expected it to read the 82v the gauge display shows but it only showed a horizontal line on the multimeter.

You'd need to check the manual for the meter for what that horizontal line means. Usually that is an out-of-range condition, meaning the meter can't read that high. If it's autoranging then check the manual for why that might happen. If it's manual ranging you need to set it to 200VDC to read an 82v pack (on 20VDC it'll read a single SLA just fine, at the 13.6-14.4v those should read when full.