Hi all, so I am working on a project. The project is adding a large hydraulic pump to a truck. It’s a 36v pump. My truck has one battery under the hood. My thoughts were to put two battery mounts on the frame behind the cab and then hook all three batteries in series to make 36v. To satisfy the electrical system of the truck I would I hook up the battery under the hood as normal with the truck side connections. I hope that makes sense as to what I’m trying to explain that I plan to do. But I want to know if my logic is correct or of any issues this may pose. Note that the truck is an old carbureted dually so the electrical system on the truck is fairly simple. And I would plan to put a higher amp alternator on the truck and it be hooked to the battery under the hood as well. Do you think this will work or am I totally off base here? Thank you!

 

Not sure what math you're using to think two 12 VDC batteries wired in any known configuration could produce 36 volts.

 

it would work until you turned the key on. then it would burn out anything electrical.
just get a 12 volt motor to drive the pump and call it good.

 

Your theory is good, I get it. Have 3 batteries in series to get the 36v. Put wires on one battery to tap off 12v for the original truck stuff. A couple problems;

1. Your 36v pump if it uses a ground on it's metal mount, would have to be isolated. One of your tap-offs for the 12v truck supply would be grounded to the frame of the truck and the engine block as all normal autos are. You could not have this ground midway coming off your battery pack, and then have another 36v ground coming off the end of the pack. You would have to carefully scope out the negative of the 36 components and make sure they are not tied to the truck frame.

2. When you do something like this, it's considered bad practice. You have 3 batteries in series, and one of them has more duties and is used more than the others. I don't know how you planned on charging the batteries, but if you have a 36v charger, the one battery that is used more to run the truck would always be behind the others. The 36v charger would bring the pack up to charge, but the one battery would always be lagging some. That is why they have a equalization mode on some chargers that you activate once a month. It brings the batteries way up in charge to try to get them all working together again. There is the danger if something happened with the truck and it completely drained the one battery, and the other two in series were still charged. If you try to use the 36v system, the other two batteries can actually charge the dead battery backwards, overheat it, and catch it on fire. It happens once in awhile in electric vehicles.

I would bite the bullet and buy 3 new batteries. Depending on what you are doing, for example using it for a dump bed, your batteries would not have to be very large.