1990 EZGO Marathon 36v with five 8 volt batteries(40v)

[xman67]

Originally Posted by JohnnieB

Had to spend some quality time with my cardiac electrophysiologist yesterday and didn't get around to checking new posts.

The question is: Can a 42V charger be used to charge a 40V (5 x 8V) battery pack?
The answer is: Maybe. It depends on the Make/Model of the charger. And it depends on whether you what a completely automatic charge, or if a timed or an attended charge cycle is acceptable.

First, what is needed? The attached recommended charge profile for Trojan wet-cell deep-cycle batteries indicates the minimum on-charge voltage per cell (VPC) the needs to be reached is 2.45VPC and the max is 2.79VPC.

There are twenty 2V cells in a 40V battery pack, so you want to reach at least 49.0V and not exceed 55.8V The ferroresonant transformer type chargers of yesteryear typically shut off when the on-charge voltage reached 2.5VPC, which would be 50.0V for a 40V pack.

A 42V ferroresonant transformer type charger that shuts off at 2.5VPC will take the 40V pack up to 52.5V, which is lower than the 55.8V max. Also, at the beginning of the charge cycle, the transformer/capacitor pair puts the transformer core into saturation, which limits the amp flow to the batteries to something like 20A typically, which is below the 22A max recommended for a 170AH battery, so it ought to work.

If a more modern charger that uses dV/dT technology (such as a DPI Accusense) is used, the charge will stop when the on-charge voltage stop increasing, so it will work also.

That is some awesome information JohnnieB! So if I am understanding correctly, the DPI Accusense 42v charger or a Lester 42v ferroresonant type charger could both charge a 40v pack and fit into the acceptable ranges for a full charge and not be above the max in the acceptable ranges?

Also, one final question I still don't have answered is- all stock parts(solenoid, motor, controller, FNR) should be ok at 40v?

I do understand they may not last as long as they would with the intended 36v.

[JohnnieB]

Originally Posted by xman67

1. That is some awesome information JohnnieB! So if I am understanding correctly, the DPI Accusense 42v charger or a Lester 42v ferroresonant type charger could both charge a 40v pack and fit into the acceptable ranges for a full charge and not be above the max in the acceptable ranges?

2. Also, one final question I still don't have answered is- all stock parts(solenoid, motor, controller, FNR) should be ok at 40v?

I do understand they may not last as long as they would with the intended 36v.

1. Yes, or at least I believe so from what I know about the way both type chargers work.

In both cases, the max amps are limited from the starting voltage, which is whatever the battery pack is at when placed on charge, until the on-charge voltage reaches about 49.5V and then start tapering off. The DPI will limit the charge current to 20A or a bit less while the Lester might be a bit higher, closer to 25A. The max amps Trojan recommends is 13%C and a T875 is a 170AH battery, so that is 22.1A. That means the Lester will be a little on the hot side, but not much and lead-acid batteries are very forgiving.

2. Motor and FNR aren't voltage dependent. Solenoid and controller are, but it is only an 11% over voltage, so they probably will work, just won't live as long.

The controller might not run immediately after the batteries come off charge due to the surface charge, but they should self-discharge below whatever the 36V controller's high voltage cutoff is in a couple hours. On the other hand, I'm pretty sure you have a Curtis 1204 controller and from what I see on the block diagram (attached), it doesn't have a over voltage shutoff.

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If you measure the amp draw of the solenoid coil, Ohm's law can be used to find the value of a resistor to add in series with the coil to drop the voltage applied to the coil down into the voltage range normally supplied by a 36V battery pack (~38V).

[xman67]

Originally Posted by JohnnieB

1. Yes, or at least I believe so from what I know about the way both type chargers work.

In both cases, the max amps are limited from the starting voltage, which is whatever the battery pack is at when placed on charge, until the on-charge voltage reaches about 49.5V and then start tapering off. The DPI will limit the charge current to 20A or a bit less while the Lester might be a bit higher, closer to 25A. The max amps Trojan recommends is 13%C and a T875 is a 170AH battery, so that is 22.1A. That means the Lester will be a little on the hot side, but not much and lead-acid batteries are very forgiving.

2. Motor and FNR aren't voltage dependent. Solenoid and controller are, but it is only an 11% over voltage, so they probably will work, just won't live as long.

The controller might not run immediately after the batteries come off charge due to the surface charge, but they should self-discharge below whatever the 36V controller's high voltage cutoff is in a couple hours. On the other hand, I'm pretty sure you have a Curtis 1204 controller and from what I see on the block diagram (attached), it doesn't have a over voltage shutoff.

------------
If you measure the amp draw of the solenoid coil, Ohm's law can be used to find the value of a resistor to add in series with the coil to drop the voltage applied to the coil down into the voltage range normally supplied by a 36V battery pack (~38V).

JohnnieB, thanks again for the info. You are right- I do have a 1204 controller. The cart is about an hour and a half away from me and I might not be able to look at it for a few weeks to a month, so I may have some more questions once I do, including how and where to wire the resistor for the solenoid.

Thank you and everyone else so much for the replies

[JohnnieB]

There is a wire from MS-3 (pedal switch) to one of the two small posts on the solenoid. Disconnect it and wrap one of the resistor leads around the post and tighten it down with the original nut.

Find a small nut and bolt that will fit through the ring terminal on the wire that was removed. Put bolt through ring terminal, wrap other resistor lead around bolt and tighten down with nut.

Now the resistor is in series with the solenoid coil.

Finding a resistor might be tricky. You want to drop about 4V and if the solenoid coil draws 1A, you will need a 4Ω resistor. A 4.7Ω is a common value and probably would work.

The resistor will need to be at least 5W.

If the coil draws 2A, the resistor would only be 2Ω, which might be hard to find, but two 4.7Ω in parallel would work.

Fortunately solenoid coils tolerate under voltage better than over voltage. Too little voltage and they don't work, too much voltage and the smoke.

[xman67]

Originally Posted by JohnnieB

There is a wire from MS-3 (pedal switch) to one of the two small posts on the solenoid. Disconnect it and wrap one of the resistor leads around the post and tighten it down with the original nut.

Find a small nut and bolt that will fit through the ring terminal on the wire that was removed. Put bolt through ring terminal, wrap other resistor lead around bolt and tighten down with nut.

Now the resistor is in series with the solenoid coil.

Finding a resistor might be tricky. You want to drop about 4V and if the solenoid coil draws 1A, you will need a 4Ω resistor. A 4.7Ω is a common value and probably would work.

The resistor will need to be at least 5W.

If the coil draws 2A, the resistor would only be 2Ω, which might be hard to find, but two 4.7Ω in parallel would work.

Fortunately solenoid coils tolerate under voltage better than over voltage. Too little voltage and they don't work, too much voltage and the smoke.

You Da Man! Thanks again