Battery equipment question...

[imagineer]

Question about pulling power from one battery in a matrix of 4 batteries. I’m building a battery powered yard cart for Mrs. Imagineer to use, primarily to tote water to the various planning beds scattered about our 2+ acres.

The drive motor for the cart will be 48vdc and be powered off 4 - 12v AGM batteries. The water tank I plan to use has a 12v pump built in that will pull about 6.5 amps. For reference, the 48v motor to run the cart is 1800 watts or 37.5 amps.

The question, would it be better to tap one of the 4 batteries for the 12v needed to run the water pump, or

should I build a voltage regulator to that the full 48v down to 12v to power the pump?

Not that it would have a significant amp draw, I’m also planning to include a USB outlet on the cart.

 

[imagineer]

I answered my own question, and will be incorporating a 48v to 12v regulator.

 

[bwringer]

I answered my own question...

How, and what did you find?

I've been helping a friend sort out some issues in a high-end electric 2-wheeled scooter (the thing is ridiculously powerful and positively terrifying) and it incorporates a wee DC/DC converter to step battery voltage down to 12VDC for the lighting.

 

[imagineer]

https://www.amazon.com/dp/B08KDFQ4JT/?tag=atomicindus08-20

I should be embarrassed. For years I've been breaking down discarded electronics (copiers, battery chargers, etc.) to recover usable bits and pieces, and I keep a spreadsheet of things like IC chips, stepper motors and drives and, surprise, voltage regulators.

Turns out I actually already have a 36v/48v to 12v regulator. I looked up the part # to review the specs, and whereas it's only a 5 amp unit, others were offered on the same Amazon page that handle 20amps.

 

[cannuck]

I have been told by an engineer that did a battery study in his graduating year that you could tap 12V from the middle of a 24V series pair of batteries and the charge will equal out with 24VDC coming in the high side. Well, did that for a few years and replaced a few batteries before switching my charging circuit in that trailer to two different maintainers. Now when on the road switch to parallel to run brakes then back to series (no brakes being used) to start/run genset.

Use the voltage reduction unit....as you have already concluded.

 

[wyliesdiesels]

ive always wondered about this. seems you would get unequal loading on the batteries and possibly shorten life of the one battery. voltage regulator would be better IMHO

 

[walta]

https://www.amazon.com/dp/B08KDFQ4JT/?tag=atomicindus08-20

Turns out I actually already have a 36v/48v to 12v regulator. I looked up the part # to review the specs, and whereas it's only a 5 amp unit, others were offered on the same Amazon page that handle 20amps.

In order for the regulator to run a motor reliably you will need a voltage regulator current rating oversized by 50% or more. If not, you risk the motors peak starting current tripping the overcurrent protection circuits in the voltage regulator and shutting down.

Being as you already own the 5 amp unit you may want to test it with your pump with water in the pump.

Walta

 

[WisJim]

I've been running house sized batteries (32v, 24v and others) since around 1977 and have always used some kind of voltage regulator/reducer/adapter instead of tapping of a lower voltage from part of the battery set. As mentioned above, it is hard on the entire set when the load is unequal on the cells. One thing we have done is to use the low amperage voltage reducer to charge a small 12 volt battery that the 12 volt load runs from.

 

[dcg9381]

ive always wondered about this. seems you would get unequal loading on the batteries and possibly shorten life of the one battery. voltage regulator would be better IMHO

Yes, this is exactly why modern battery systems (lithium) have internal means to "balance" individual cells... Basically they're a big stack of smaller batteries and you can't be sure that the cells charge/discharge the same.